RADAR BULLETIN No. 1
(RADON)

THE TACTICAL USE OF RADAR

 

UNITED STATES FLEET
HEADQUARTERS OF THE COMMANDER IN CHIEF

FF1/S67 Serial 0359

UNITED STATES FLEET HEADQUARTERS OF THE COMMANDER IN CHIEF NAVY DEPARTMENT, WASHINGTON, D.C.

March 9, 1942.

Radar Bulletin No. 1 is issued for the information and guidance of Naval personnel concerned with the operation of Radar equipment and with the application of information received by means of this equipment.

This bulletin is a confidential, non-registered publication and shall be safeguarded as required by U.S. Navy Regulations, Article 76. It is assigned class "C" stowage. Authority is hereby granted to reproduce the Radar Plot Nomogram and Peg Board for plotting purposes. No other material herein may be reproduced without authority of the Commander in Chief, United States Fleet.

When the destruction of this bulletin is ordered, or becomes desirable, it shall be destroyed by burning. No reports of destruction are required.

/signed/
RUSSELL WILLSON
Chief of Staff

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CONTENTS

		Page
I.	INTRODUCTION	1
II.	THEORY AND OPERATION OF RADAR	1
III.	TYPES OF RADAR EQUIPMENT	4
IV.	CAPABILITIES OF RADAR EQUIPMENT	7
V.	LIMITATIONS OF RADAR EQUIPMENT	9
VI.	THE RADAR TACTICAL ORGANIZAT4ON AND ITS FUNCTIONING	14
VII.	OPERATIONAL USE OF RADAR AT SEA	31
VIII.	OPERATIONAL USE OF RADAR IN HARBOR	35
IX.	USE OF RADAR BY SUBMARINES	36
X.	MISCELLANEOUS OPERATING NOTES	37
XI.	FIGHTER DIRECTION FROM AIRCRAFT CARRIERS	38
XII.	CONCLUSION	45

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REFERENCE PUBLICATIONS

The following is a list of available technical and tactical publications upon which this bulletin is based.

1. "Radar Technical Bulletins." (Eng.129) (Confidential).
   No. 1. "General Information on Radar Equipment."
   No. 2. "Estimating the Altitude of Aircraft by Radar Observation."
   No. 3. "Amplidyne Control of Radar Antennas."
   These bulletins are published by the Bureau of Ships.

2. Ordnance Pamphlets (Confidential).
   ORD 656. "Operation of Fire Control Radar Type FA."
   ORD 657. "Operation of Fire Control Radar Types PC and FD."
   These pamphlets are published by the Bureau of Ordnance.

3. "Tentative Radar Doctrine." (Revised October 6, 1941)
   Commander in Chief, U.S. Pacific Fleet Operation Order No. 31-41.

4. "Tentative Doctrine, for Fighter Direction from Aircraft Carriers."
   This is enclosure A to CNO confidential letter Op-22 (GB/IC) (SC) S67/S71 serial 0208222 of August 6, 1941. Subject: Fighter Protection of a Naval Force.

5. "Radar in Pacific Fleet Landing Exercise Number One."
   Commander Scouting Force confidential letter to CNO S67(1)/(95) serial 0814 of October 13, 1941.

6. "Radar Installation Plan."
   Bureau of Ships C-S67/36(485) C-EN28/A2-11 of July 11, 1941 (with changes).

7. "Instructions for Fighter Direction." CSP 1291.
   "Vocabulary for Fighter Direction. CSP 129.2.

8. "Essentials of Various Types of Radar Equipment."
   CNO confidential letter Op-22 (QB/IC) (SC) S67/S71 serial 0212622 of October 8, 1941.

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THE TACTICAL USE OF RADAR

INTRODUCTION

The object of this bulletin is to enable the officer personnel of ships and operating forces to make the most efficient use of Radar equipment that is installed in their ships, by providing them with available information on operating experience in the use of Radar gained by both the British and United States Fleets. It is intended that this pamphlet serve as a guide to officers other than those having direct cognizance of the technical or operational aspects of Radar. It is not to be considered as a final Radar doctrine.

Radar equipment is constantly undergoing improvement in design, so hard and fast rules for its tactical use cannot be laid down. Revision of this pamphlet may be expected as dictatedgby-experience of the operating forces afloat and., new ievelopmentsin equipment.

THEORY AND OPERATION OF RADAR

A. Theory

In order that all officers concerned may have a general knowledge of the theory of Radar opertion, the following brief notes are presented.

Radar operation consists of sending out a series of impulses of electromagnetic energy from from a high-power, ultra-high-frequency radio transmitter. These impulses are directedinto a beam by a directional antenna, reflected by objects which they strike, received by the same antenna, and into a radio receiver. Only a small portion of the transmitted energy is reflected back to the antenna. The interval between the transmission of successive impulses is suffienctly long for ech one to go out and return from a target at the maximum range of the set. Thus there is no interference between returning echoes. The transmitter and receiver are so operated that the time (several huyndred millionths of a second) between the transmission and reception of each impulse can be measured and converted into a range which is indicated by the position of a "pip" on the screen of a cathode ray tube In order to provide a steady range indication, a large number of impulses are transmitted each second.

The diagram on page 3 gives a graphic description of Radar operation. The function of the duplexing system shown on the diagram is to keep the outgoing pulse out of the receiver and the echo pulse out of the transmitter.

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Directivity (bearing) is obtained by a rotating directional antenna which, when used with a gyro compass repeater, provides true bearings. Radar bearings may be fed into the target designation system and indicated in the Pilot house, air defense forward, and Radar Plot.

Radar elevation angle is obtained directly from a dial showing antenna elevation angles on the fire control sets. The longer range detection sets have no feature which permits satisfactory altitude estimates of aircraft targets, which is of great importance in fighter direction. A rough estimate of altitude can, however, be made by use of carefully prepared calibration charts using null points. Radar Technical Bulletin No. 2 fully explains the preparation of these charts and their use.

B. Reliability of Radar Ranges and Bearings

1. Range.

Ranges obtained with properly functioning Radar equipment are generally more reliable than those obtained with ordinary coincidence or even stereoscopic rangefinders. This is particularly true in the case of fire control Radar equipment. For example in the Hood-Bismarck incident, the Hood's optical rangefinder identified the opening range of the Bismarck as 23,000 yards, whereas the corresponding Radar range was given as 27,000 yards. The range given by the optical rangefinder was used and the opening salvo fell short by approximately 4,000 yards.

Several conclusive arguments may be advanced in support of the reliability of Radar range over optical range:

1. Errors which may exist in Radar ranges are essentially constant throughout each range scale and are relatively small.

2. At the outset of an engagement that the human element will cause errors in ranges obtained Optically, especially in extreme ranges. On the other hand, Radar ranges appear on the cathode ray tube unaffected by the human element. I can be determined immediately whether a Radar range is available for use, because the ranges either appear on the screen or they do not.

3. Signal strength does not materially affect the accuracy of Radar range, since range appears on the screen of the cathode ray tube as a linear dimension with quantitative significance, viewed at right angles to the line of vision. That is, the range is indicated instantly by the point at which the signal appears on the screen.

4. Quite often at ranges over 20,000 yards, the first indication that the fire control party receives of a change of target course will come from the Radar operators.

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It is, therefore, of the utmost importance that all ship's Radars be maintained in perfect operating condition at all times.

Too much emphasis cannot be placed on the need for periodically calibrating all Radars. There are several types of characteristic errors which exist in all types of Radar equipment, and only by frequent, accurate calibration can the correct zero setting be determined for each set at all times.

Radar carelessly used will give ranges as accurately as optical equipment carelessly, used. Radar expertly kept up and skillfully used will give range accuracies far better than any optical equipment however expertly maintained or skillfully used, particularly at ranges in excess of 10,000 yards. Therefore, when disagreement exists between Radar range and optical range particularly at ranges in excess of 10,000 yards, it is safer to use Radar range.

In connection with the foregoing it must be pointed out that Radar in the hands of inexperienced operating and maintenance personnel is of little value. Also it should not be supposed that a maintenance man is an expert just because he has graduated from a Radar school.

2. Bearing

Under conditions" of good* visibility; and when the target is within the range of vision, bearings obtained Optically are always more accurate and reliable than Radar bearings, and should be used in preference to them. As far as bearing is concerned Radar has the advantage only when visibility is poor or the target is outside the visible range.

TYPES OF RADAR EQUIPMENT

The following three types of Radar equipment have been developed:

1. Detecting Equipment (Navy Model Series S)
2. Fire Control Equipment (Navy Model Series F)
3. Recognition Equipment (Navy Model Series B)

Experimental equipment of these three classes are given the usual CX or X model assignments. Radar apparatus designed for use in air-craft is assigned in the Navy Model Series "A" succeeded by "S," "F," or "B" (in accordance with the functional classification of the Radar equipment) followed by an alphabetical designation letter.

A. Detecting or Ship Control Radar

This type includes Models CXAM, CXAM-1, SA, SC, SC-1 (improved SC), SG, SH, SD, and SJ. The latter two models are designed for installation in submarines.

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Characteristics of Radar Equipment
Model	Purpose	Reliable Range on Surface Ships (Miles)	Reliable Range on Large Planes (Miles)	Range Accuracy (Yards)	Bearing Accuracy (Stationary Target)
CXAM (6 sets) CXAM-1 (14 sets)	Medium range ship and aircraft detector installed on some BB, CA, CV and AV.	5-10	35	±200	±1½°
SC SC-1 (improved)	Medium range aircraft detection radar for BB, CA, CB, CL, CV, DD and other vessels	4-10	10-25	±100-200	±½°
SC with CXAM-1 antenna	One installation in USS Wasp	Performance should be superior to CXAM-1 and SC, but no reports of tests are available
SD	Aircraft warning device for submarines. Antenna is non-directional.	5	12	±500	---
SH	Surface craft detector for ships	7-14	---	±25	±¼°
SJ	Ship detector for submarines with torpedo FC application	3-6	---	±25	±½°
FA	General purpose detecting and fire control radar. 10 manufactured. now being replaced by model FC	3-5	9-15	±50	±¼°
FC	Main and secondary battery director radar	5-10	---	±25	±¼°
FD	Antiaircraft and double purpose battery director radar	5-10	5-15	±10-15	±¼°
FK (Mk. 8)	Main and secondary battery director radar to replace model FC	5-10	---	±25	±6'
ABA BI	Identification equipment used with radar
IFF Mk. II	British set installed in a number of VPB	Employed principally to identify our planes to British ships and ground stations
IFF Mk. II N (ABD)	British set on order in large quantities	This equipmnt can be used with certain SC and CXAM-1 sets as well as British detection equipment

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The function of detecting Radar equipment is to act as a general searching device to obtain indications of the presence, range and bearing of unknown ships or aircraft. Primarily this function involves detection of such craft at ranges greatly in excess of that at which visual observation or gunfire would be effective.

Since maximum range is dependent on height of antenna, ship control Radar antennas are always installed at the highest possible points of the ship.

Ship control equipment and fire control equipment in the same ship have fundamentally different characteristics which allow them to perform their primary functions best, generally at the expense of the other functions. Thus in order for detecting equipment to obtain echoes from aircraft at the long range mentioned above, some sacrifice is made of effective range at low altitudes, accuracy of range and bearing, and degree of resolution between targets. For these reasons a ship control Radar set is a good aircraft detector but a poor surface craft detector. Similarly a main battery fire control Radar set is a good ship detector but a poor aircraft detector.

B. Fire Control Equipment

This type of Radar equipment includes Models FA, FC, FD, and FH. In addition the Model SJ detecting set for submarines embodies a torpedo fire control application.

Radar equipment which is connected, with fire control apparatus is designed to obtain ranges and bearings accurately and, in the case of anti-aircraft director equipment, also elevation angle. This equipment supplements optical rangefinders and fire control equipment. The effective range, because of the mounting of antennas on directors or at other points not usually as high above the waterline as those used for detecting equipment, may be less than that of the latter type of Radar. The range of anti-aircraft director Radars should be much greater than that of similar optical devices and the equipment will function accurately under conditions precluding the operation of optical equipment.

As mentioned above, main battery fire control Radar equipment is better for surface craft detection than for aircraft detection. Its other important function is searching for surface craft during periods of reduced visibility, or for shadowing aircraft flying at low altitudes. On clear days, one can see any ship farther than Radar can pick it up. Once the ship is within Radar range, however, the ranges are more accurate than those from optical instruments, except when the range is quite near.

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C. Identification Equipment for Use With Radar

Radar identification equipments include Models BI and ABA (Aircraft). In addition there are two types of British IFF (identification, friend or foe) equipment being installed in some of our planes. These are the IFF Mk. II (SCR 535) and IFF Mk. II N. (Model ABD).

Recognition devices are designated to furnish a means of identifying unknown targets, either surface ships or aircraft, when they have been detected by the Radar set. The operation of the identification equipment, usually controlled automatically by the Radar, transmits a signal which is observed by the Radar operator, thereby identifying the craft as friendly. The absence of such a signal, however, does not identify the craft as an enemy, since, if it is a friendly ship it may have no IFF equipment or if it does have the equipment it may not be functioning properly. Obviously to be totally effective, identification equipment must be universally installed in all friendly ships and aircraft, but at the present time this condition is far from having been attained.

D. Aircraft Radar Equipment

There are two classes of airborne Radar equipment:

1. ASV Detecting set for use against, surface vessels.

2. AI Detecting set for use against others aircraft, particularly for installation in night fighters.

IV. CAPABILITIES OF RADAR EQUIPMENT

More complete data on Radar sets is to be found in the reference publications but for the sake of ready, reference a table of Radar characteristics is given on page 5. It should be noted that the figures in this table are average only. Individual sets of a given Model classif ication may give results which are in excess or fall short of those listed for that particular model. Therefore careful records of the performance of each set should be kept at all times in order to determine its capabilities under various conditions. Radar can be used to the best advantage only when the operating personnel know what their particular set will and will not do.

A. Capabilities of Detecting Radars

Ship control Radar sets properly operated will permit the following being carried out:

1. Warning of approaching aircraft before they can be sighted visually, so that; AA defense may be brought to the proper degree of readiness in sufficient time, and other necessary defense measures may be taken.

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2. Warning of the presence of enemy surface craft that are beyond the visible range, so that the correct, disposition of the fleet may be made to meet an attack, or preparation made to attack the enemy by surprise. It must be remembered that Detecting Radar equipment is more effective for No. 1 than for No. 2.

3. Indication to be given to other ships in own force of the direction from which either an air or surface attack will develop.

4. Fighters to be flown off in time if an air attack is imminent and a carrier is in company.

5. A fighter escort to be called for in sufficient time if no carrier is in company.

6. Constant observation of the movements of enemy aircraft, once detected, and the direction of own fighter planes to a position suitable for interception.

7. Provision of security against night attack, attacks during conditions of poor visibility, or from behind a smoke screen.

8. Scouting.

9. Screening.

10. Obtaining'bearings (but not ranges) of other Radar equipped ships up to considerable distances; greater than the maximum at which echoes can be received.

11. Obtaining meteorological data from balloons.

12. Obtdining range and bearing of prominentt landmarks and large buoys, thus serving as a navigational aid at night and during Iow visibility. When ranging on the shore line echoes from higher land farther inland must not be mistaken for the shore itself.

13. Ranging on distant land up to 200,000 yards.

14. By keying the CXAM transmitterit has been found possible to communicate between ships equipped with this type equipment.

B. Capabilities of Fire Control Radars

1. Supplying of smooth, accurate ranges and fairly accurate bearings and elevation angles to the computer so that a solution to the frire control problem may be obtained earlier than by optical means. This is especially advantageous at night and during periods of low visibility when the use of optical instruments is precluded. When

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using fire control Radar apparatus it is at present advisable to obtain bearings optically whenever possible, and supply only ranges from the Radar in order to obtain the most accurate solution of the fire control problem. Using this method, success has been obtained in arriving quickly at a satisfactory solution in the rangekeeper. Smooth range inputs allow full use of rate control methods to produce in about one half the time required with optical ranging, a rangekeeper solution that will held oh the target without variation.

2. The detection of surface craft during periods of reduced visibility.

3. The detection of low flying enemy shadowing aircraft.

4. Supplying useful tactical information such as the position of other ships in own force, and greatly facilitating station keeping at night when all ships must be darkened.

5. Acts as a distant limited warning device in the absence of ship control Radar equipment. It should be noted here that if a fire control set becomes inoperative, the ship control set may be used for fire control purposes,, but it will supply less accurate data.

6. Supplying data for the direction of starshell or searchlight illumination.

7. Spotting by ranging on shell splashes. At short ranges it is possible to follow the projectile with the radar. This will give an indication on the screen as of a mouse running along under a sheet. Echoes from over splashes may not show up on the screen because of being hidden by the larger target echo. Spotting in bearing will not be feasible, as the splash does not last long enough to permit the antenna to be trained on it accurately.

8. Ranging on distant land up to 150,000 yards.

V. LIMITATIONS OF RADAR EQUIPMENT

Radar has certain limitations, and certain difficulties may be experienced in its use. It is well to have a good, knowledge of these in order that too much will not be expected of any Radar set.

A. Rapid development of Radar equipment without extensive trials means that all sets may be expected to have many minor defects at first. Every effort is made to remedy these on the production line but some can probably be worked out by the ship's Radar material personnel. Many ships already equipped with Radar have reported trouble due to the fact that the installations have been made with too great haste, improper attention having been paid to some of the more important details of the work.

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B. The effectiveness of Radar is largely dependent upon the skill and experience of the operator. Operating experience shows that at least 50 hours is required before an operator begins to acquire any degree of proficiency, and a much longer period must elapse before he can be classed as an expert. A skilled operator should readily be able to determine the nature of a target whether aircraft or surface vessel, and to distinguish between a single target and a few, a few and a group. The latter is closely tied up with the inherent resolutions of the Radar which varies for the different models. While visual acuity is of importance, judgment is actually the deciding factor in expertness.

Constant watchkeeping imposes a great strain on operators, especially when counter radio direction finder (RDF) measures are being employed. Experience indicates that half an hour is the longest period an operator can watch the range scope at any one time. Watches should, therefore, be two hours long, and two operators should be assigned to each watch. They should alternate as actual operator every half hour. On fire control equipment the one who is not operating can act as trainer.

C. The possibility of a ship's position being disclosed to the enemy by radio direction finder (RDF) bearings being taken of its Radar transmissions must never be overlooked. The danger of such detection may, however, be minimized by the use of appropriate counter RDF measures.

Radar transmissions on the higher frequencies are less susceptible to interception by radio direction finder receivers than are those on the lower frequencies. Unfortunately, most of the sets we have in service now can probably be detected by shore based RDF sets or by special shipboard RDF sets on the larger ships. It is quite likely that accurate bearings on Radar transmissions can be taken up to 250 miles and, on some occasions, with less accuracy and certainty at greater ranges. A point which must always be remembered is that Radar transmissions can be intercepted at much greater ranges than those at which echoes can be obtained. This is an advantage both to our own forces as well as those of the enemy.

D. It is believed possible for certain types of aircraft to take bearings on Radar transmissions.

E. The scarcity of identification equipment on our own ships and planes at the present time gives rise to one of the greatest problems in Radar operation. Without such equipment it is possible to identify the target sighted only with the greatest difficulty. The searching ship can identify the unknown ship only by tracking it for an appreciable length of time, and the effectiveness of this method presumes a comprehensive knowledge of the movements of friendly ships and planes in the vicinity. Obviously during periods of radio silence complete information ofthis nature can be obtained only with the greatest difficulty, if at all.

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F. Since Radar operation depends on a clear radio line of sight between the Radar antenna and the target, the range at which a target may be detected is dependent on its height above the horizon. (On rare occasions atmospheric conditions may be such that the waves are refracted and the Radar will detect objects at long distances beyond the horizon). It is quite possible for low flying aircraft or high speed surface craft to approach to within the visible range before being detected by Radar (not so likely if fire control equipment is being used for searching), particularly when counter RDF measures are being used. It is essential that a good lookout be kept even though the Radar is being used.

G. Minor side lobes of radiation from antennas of some types of Radar equipment will cause echoes to appear from a target even though the antenna is trained considerably to one side of the target. These lobes may, however, be readily distinguished, since they are. at exactly the same range as the main signal/(but of lessv signal strength), and since they have a definite bearing relation to the main signal.

H. The effective range at which submarines can be vdetected by means of Radar is comparatively short because of the small reflecting surface which such targets present. Reliable signals may be obtained up to about two miles on surfaced submarines, although on several occasions they have been detected at as much as nine miles. Tests of Model SC with a submarine target indicate that detections may be made at a range of about one mile when the target is at periscope depth (periscope showing), and at 1½ to 4 miles with the conning tower showing. Present equipment is used tp the best advantage against submarines during periods of reduced visibility.

I. Local radio transmissions on Radar frequencies (e.g., the homing beacon in carriers and TBS radio equipment) may cause serious interference with Radar operation. High power radio transmissions in the vicinity may interfere with Radar operation. And where there are a number of Radar sets operating on the same frequency in the same force, interference may be expected to occur between them. While it is usually possible to range satisfactorily in the presence of interference, an additional strain is placed on the operator, and occasionally the interfering signal may momentarily blank out the desired echo. The existence and extent of such interference should be determined in each ship and steps taken to insure againstjamming of the Radar at a vital moment. No difficulty should be experienced in Radar interfering with radio communication circuits, because our communications receivers are so designed as to preclude the occurrence of suchinterference. Radar has, however, been known in several instances to cause interference on the DP-5 direction finder receiver and on the QC sound gear.

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J. It is known that the enemy has equipment capable of jamming our Radar and rendering it entirely ineffective. When such jamming occurs the only remedy is to shift to another Radar set on a different frequency. For example, if the ship control Radar were jammed, one of the fire control sets would have to be brought to bear on the same target. During the recent Scharnhorst-Gneisenau action in the English Channel the British shore based Radars were so effectively jammed by the enemy as to make it impossible to use them. The enemy, in this instance, employed frequency modulated CW signals. The probable appearance of the various effects is indicated on page 12.

All ships, when using Radar, must be constantly on the alert for jamming which, when it occurs, will come suddenly and unexpectedly. Steps must be taken to meet it instantly if the favorable outcome of the engagement is not to be given to the enemy.

K. False contacts which confuse the issue may be obtained from ionized clouds, and are most common around mid day. These signals are precise, the signal strength approximating that of a tug or some small craft, and the bearings and ranges indicate contact on an object moving on a definite course at a definite speed. Contrary to expectation, exact bearings can be taken on the signal, indicating a concentrated mass of ionized air. These contacts are very hard to prove false. :In normal cruising during good visibility they present no problem for it is easily determined that there is no target, and rational means can be utilized to find the cause; but at night, steaming at darkened ship, the time factor does not permit the determination that the signal is definitely false. Action must be taken immediately by ship control before confirmation can be ascertained. False contacts on clouds may be determined by:

1. Coordination of the plotted course and .speed ;bf the target with the aloft wind data.

2. Use of an FC or FD Radar to obtain position angle. If the position angle is above the horizon and the target speed is less than 50 knots, it is reasonable to assume that a cloud contact has been made. This check, however, requires time, for it is difficult to get an FC Radar on the target, and in most cases it is impossible to get an FC Radar signal from elevated targets beyond 6,000 yards. The FD should be much better than the FC for this purpose.

L. Additional confusing echoes may be obtained from distant mountains, wave tops in a heavy sea, and possibly from enemy Radar transmissions.

M. Because of the transmitted pulse which blocks the receiver to a certain extent and causes a large pip to occupy the initial portion of the trace on the cathode ray tube, each Radar set has a minimum range within which it is impossible to make detections. This range varies from under ½ mile to slightly over 1 mile, depending on the type of equipment.

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N. It is possible and comparatively easy for the Radar operator to range on the wrong target, and this problem is of vital importance when planes are operating in the vicinity of surface ships. If the range to the plane is near the range to the ship, it is likely that the operator will obtain a range to the plane. It is considered advisable, therefore where possible, to check the range by an estimate from the spotter.

Similarly when an attacking formation, which has been tracked for some time, breaks up, much confusion may result because of the difficulty of deciding which target to follow with the Radar.

O. Ice conditions prove very detrimental to Radar operation, for not only does the equipment fail to function properly when the antenna is covered with ice, but ice covered targets give a very weak signal and often cannot be detected at all.

P. Much of the effectiveness of Radar is lost unless orders and data from Radar contacts can be transmitted to the ships concerned in a minimum of time. A suitable vocabulary is necessary for rapid transmission of Radar information and instructions on the Radar warning net.

VI. THE RADAR TACTICAL ORGANIZATION AND ITS FUNCTIONING

With elementary knowledge of the capabilities and limitations of Radar it is possible to consider the Radar Tactical Organization and how it should function. This section is based directly on the CINCPAC Tentative Radar Doctrine of 6 October, 1941. Briefly, the Radar Tactical Organization consists of a number of Radar Guard Ships, a Radar Control Officer, Fighter Direction Officer, Radar plotters, and operators. The duties of the Fighter Directing Officer and his own organization will be taken up more completely in the section on Frighter Direction from Aircraft Carriers.

Radar Control

1. Duties

Radar control should, as a rule, be a function of O.T.C. who should:

1. Assign sectors of Radar responsibility if other than a standard disposition has been ordered.

2. Maintain a continuous .plot of all warning net information.

3. Evaluate plots and transmits appropriate nAlerts of impending surface or submarine attack. Note: It is the function of the F.D.O. to transmit "Alerts" of impending air attack.

4. Order which Radar policy is to be effective.

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5. Advise Radar Guard Ships of known movements of own or enemy air or surface craft. Normally, the O.T.C. will not transmit current Rador information of enemy aircraft in the vicinity, since that is the function of Commander Air (FDO).

6. Order any guard ship to shift target, search 360°, or report position of friendly fighters as necessary.

2. Radar Control Reliefs

The sequence of Radar Control reliefs should be the same as the chain of tactical command. Relief Radar Controls should be prepared to take over at any time.

3. General

Whenever possible at night or during periods of low visibility Radar watches should be maintained in the O.T.C.'s ship only, since then the Radar policy is more .easily controlled, and signaling and delays are obviated. This, of course, presumes that one Radar is sufficient for a thorough search; a condition which will exist rarely.

When a target has closed sufficiently for fire control Radar equipment to be brought into operation against it, Radar Control should designate one or more ships to continue keeping a warning watch as a precaution against attack by additional enemy units.

B. Radar Guard Ships

1. Function

The reason for detailing Radra Guard Ships is that the entire horizon may be more quickly and thoroughly searched by a number of ships each searching a definite sector than by one ship searching the entire 360°. Generally, however, an all round search by each guard ship is preferable, but a sector watch is desirable as providing particular security against low flying aircraft or high speed surface craft, or when the probable direction of an enemy approach is known.

2. Assignments

1. In each assigned sector of Redar responsibility there should be established a sector Radar Guard Ship.

2. When a sector of Radar responsibility contains more than one Radar ship, the senior task group or unit commander in the sector should assign watches, enforce Radar discipline to minimize interference, and provide for immediate relief in case of casualty.

3. Carriers should not normally be assigned as sector guard ships. They will be the ships from which Fighter Direction is conducted

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4. Radar guard Ships should normally be stationed in or beyond the outer screen. Whenever possible they should be within easy visual signaling distance. If ships are in line ahead, the Guard ship should haul slightly out of line.

3. Duties

1. Conduct continuous search of assigned sector employing appropriate counter RDF measures or such Radar policy as Radar Control may order.

2. When a new contact is made, transmit an initial report to Radar Control. The extreme importance of transmitting this initial report immediately not only to Radar Control but to all non Radar ships as well cannot be overemphasized. During recent operations in the Pacific, Radar warnings of approaching aircraft were usually so late in being delivered to non Radar ships as to negate the value of the Radar installation.

3. Track and plot each contact in own sector. When data obtained is sufficient to determine enemy intentions, transmit amplifying reports from which the F.D.O. can contact enemy with own Radar, and O.T.C. can base orders and issue Alerts to the ships in the force. If possible the amplifying reports should include the number of enemy units, bearing and distance from Fleet Center, course, speed, altitude, and time. The first amplifying report should be made at the earliest possible moment even though the information is not entirely complete. Subsequent amplifying reports need be made only when changes in major variables (course, speed, altitude) occur. Although it is desirable to report the bearing and distance of the target from Fleet Center, it will usually be more convenient, and save more time to report bearing and distance from the reporting ship. Special care must be taken to report the correct bearing. In one recent action, enemy, planes were reported (incorrectly) as approaching on a certain bearing, but since they actually came from a different direction the value the Radar Report was completely nullified.

4. When Radar Guard Ships are making sector searches some provision must be in force so that when one ship makes a detection and commences tracking, its sector will not remain unguarded. There are numerous ways in which such a system can be worked out depending on the number and disposition of the guard ships, and considerable latitude should be allowed each Radar Control in working out a method which will best suit his particular situation. Some possible methods are:

   1. Each Radar Guard Ship searches entire 360°. All operators may then concentrate upon several attacks coming from roughly the same bearing. If It may lead, however, to several operators reporting the first attack, each being under the impression that the others are reporting subsequent attacks, unless much practice may be had in the assignment of targets between them.

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2. Radar Guard Ships employ sector searches, while fighter Directing Ship searches the whole circle. When a target enters the sector overlap between adjacent sector guard ships, the guard ship whose sector the target is leaving notifies the guard ship whose sector it is entering. The latter notifies the former when it has located the target and assumes responsibility for it, and the former does not relinquish the target until this notice is received. This system will probably prove the best in most cases.

3. Radar Control Ship takes over search of the sector originally covered by guard ship which has made a detection and is now tracking.

4. When one Radar Guard Ship makes a detection the two ships covering the sectors on either side, enlarge their sectors so. as to include that originally covered by the ship,making the detection.

5. Notify the sector commander or Radar Control in case of casualty or Radar activity beyond own capacity to track and plot.

C. Fighter Direction Ship

1. Duties

Fighter Direction should normally be a funtion of. Commander Air who should: :

1. Maintain a continuous plot, of all Radar information affecting air operations,

2. Evaluate plot and transmit appropriate Alerts of impending air attacks.

3. Launch combat patrols on order, or (unless specifically ordered to the contrary) without order whenb definite Radar contact with enemy aircraft is obtaIned.

   The number and disposition of combat patrols should be at the discretion of Commander Air, but the section designations of patrols launched or recovered should be communicated to Radar Control, Relief Radar Control, and the Radar Guard Ships.

4. Utilise own Radar to the best advantage to supplement information from Radar Guard Ships, and transmit evaluated information from own Radar when it is pertinent to the general tactical situation.

5. Issue standard instructions for combat patrols and special instructions as may be required in particular circumstances.

6. Direct interception of enemy aircraft by own fighters.

7. Transmit notice of completed interceptions.

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2. Typical Sequence of Fighter Director Reliefs

1. Commander Air.
2. Carrier Division Commanders in order of seniority.
3. Carriers in order of seniority.
4. Air Task Group cruisers in order of seniority.
5. Battleship Division Commanders in order of seniority.

Relief Fighter Directors will be prepared to take over at any time.

D. Other Radar Ships

1. Normally ships not detailed as Radar Guard Ships may use their Radar within the limitations of the Radar policy which is in effect at the time. In their case reports should be made only when guard ships fail to report in accordance with the system in force within a reasonable length of time.

2. If no Radar Guard Ships have been detailed, ships should report any unidentified contact which might endanger the fleet.

3. When particular security is required, orders should be given that only Radar Guard Ships and Radar Control are to transmit. The other ships may, however, keep a receiving watch. There should never be any restriction on transmission when air or surface attack is known to be imminent, and it is obvious that the enemy is aware of our own position.

Radar Communications

1. Fundamental Considerations

Rapid communication among vessels of a group is essential both to report Radar contacts and exercise Radar Control. In actual practice visual, radio telegraph and radio telephone have been tried. Only radiotelephone has proved sufficiently rapid where attacking aircraft have been involved. Visual should not be used at night and often cannot be used in reduced visibility.

Once it has been decided to accept the risk of disclosure or interception necessary to use Radar, a common radio telephone circuit should be available to all ships operating in a disposition. The frequency and power used for this circuit must be such that the probable range under all conditions will be less than the direct transmitting range of the Radar. Super frequency equipment, similar to Model TBS, using low power, is the only means now available.

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Therefore, in order to coordinate Radar, disseminate information and, when necessary, maneuver the disposition; it is essential that Model TBS or its equivalent be installed in large vessels such as carriers, heavy cruisers and battleships as soon as possible.§. This has been authorized. A task force commander is usually in a large ship which is accompanied by smaller ships. It is necessary that large ships, particularly flagships, be able to work super frequency radiophone with small ships or escorts. Only thus can proper coordination be effected rapidly with a minimum chance of enemy radio detection or interception.

It is desirable to use frequencies above 250 mcs. However, since equipment will not be available for some time, some immediate arrangement is needed. Almost all small vessels are already equipped to use frequencies of from 60 to 80 mcs. Therefore,'only a relatively small number of additional TBS or similar equipments would be needed. During the next few years, due to the present sun spot cycle, frequencies above 60 mcs. will probably be relatively free from sporadic ionized layer reflection. Refraction in the lower atmosphere, known to extend the range of 60 mcs. transmissions to over 100 miles can be greatly reduced by using low power.

Thus for all practical purposes, TBS equipment on low power can be used dn 60 to 80 mcs. for invaluable short range oommunication with limited assurance that interception by enemy surface craft over 40 miles away is improbable. Interceptionby specially equipped enemy aircraft is, of course, possible at greater distances. But if low power with low antennas is used, the chances of interception over the horizon are remote. Multiple whip antennas at convenient points just below bridge level are needed to avoid blind spots when using low antennas. Effective ranges to surface craft can be reduced to 10 or 15 miles, if desired.

2. Warning Net

Warnings of impending attacks should be transmitted immediately on the Warning Net by the Radar equipped ships designated for this duty by the O.T.C. All ships should insure that the Radar Warning Net Circuit is accurately tuned and that the information received on this net is communicated instantly to the Captain1 andv Gunnery Control.

In addition to traffic assigned to the warning net by U.S.F. 70 the following communications should be handled on this curcuit:

1. All reports by Radar Guard Ships.

2. Orders from Radar Control or Fighter Director to Radar Ships.

3. Alerts by Fighter Director with respect to air attacks, and by Radar Control with respect to surface attacks.

4. Notice by Fighter Director of combat patrols launched or recovered.

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3. Fighter Net

The following oommunications should normally be handled on this circuit:

1. Orders to combat patrols.

2. Reports from combat patrols.

3. Orders from Fighter Director to carriers to launch or recover patrols.

4. Reports from carrier relative to launching or recovering patrols, etc. (To include section color designations).

4. Circuit Instructions

1. Separate circuits should be provided for Fighter Net and Warning Net in order to handle the volume of traffic expected during major air activity against a large fleet disposition. In smaller dispositions and during periods of minor air activity, these two communication circuits may be combined on a common frequency by O.T.C. Traffic on both circuits should be broadcast without receipt oracknowledgment, except that air craft units will acknowledge for receipt of orders.

2. Circuits should as a rule, be manned as follows, available equipment permitting:

   	Fighter Net		Warning Net
   	Transmit	Receive	Transmit	Receive
   O.T.C. (Radar Control)	--	X	X	X
   Relief Radar Control	--	X	X	X
   Fighter Director	X	X	X	X
   Relief Fighter Director	X	X	X	X

5. Form of Radar Reports

To facilitate plotting, Radar reports should be made in the following form:

1. Type and number of targets; that is, air or surface, one, few (2 to 10), many (over 10).

2. True bearing from Fleet Center. For convenience and speed this may be given as true bearing from reporting ship.

3. Distance in miles from Fleet Center. This may also be given as distance in miles from reporting ship. Radar Control can convert to distance from Fleet Center.

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4. Course (true).*

5. Speed (knots).*

6. Altitude (if approximate, use low, high, very high).*

7. Zone time of the above data.*

8. Additional pertinent information, if any.

9. Call of originating ship.

* These items should not be required in initial reports. As many of them as can be determined without undue delay should be included in an amplifying report which is to be used as a basis for interception.

Examples .

Initial report by Radar Guard Ship:
FEW BANDITS, TWO ONE ZERO, FOUR SIX, CAST TWO NINE.

Amplifying report by Radar Guard Ship:
FEW BANDITS, ONE EIGHT FIVE, THREE ZERO, ONE ONE ZERO, ONE FOUR ZERO, VERY HIGH, ELEVEN FOURTEEN, CIRCLING FLEET TOWARD BEARING OF SUN, CAST TWO NINE.

6. Vocabulary

Standard phraseology should be used by all Radar operators in reporting information to Radar Plot and other control positions. The vocabulary used in Fighter Direction and on the Radar warning and fighter nets should be used whenever possible, in this way all personnel concerned with handling Radar information will use common terms, brief and clear, which will leave no doubt as to the information conveyed. The need for a uniform, brief, and clear form of exchanging Radar information rapidly cannot be over emphasized.

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If desired, the more important phrases could be given in examples such as:

RADAR OPERATOR REPORT	MEANING
"FEW BANDITS, ZERO FIVE FIVE, DISTANCE THIRTY FIVE AWAY."	"Two to ten enemy aircraft, bearing 055 true, distance 35 miles going away."
"BLUE FIGHTERS, ONE FIVE ZERO, DISTANCE THIRTY."	"Our blue sections of VF, bearing 150 true, distanoe 30 miles."
"LARGE BANDIT, TWO FIVE ZERO, FADING. AT FTFTY."	"The Radar Signal from a large group of enemy aircraft which is being tracked on bearing 250 is fading at 50 miles indicating the edge of a null band."
FIGHTER DIRECTOR'S ORDERS TO RADAR OPERATOR	MEANING
"TRACK BANDIT ONE FIVE ZERO, DISTANCE THIRTY."	"Follow the enemy aircraft, 150 degrees, 30 miles, making reports about every 15 seconds or when signal fades or reappears."
"TRACK FOR INTERCEPT, BLUE FIGHTERS AND LARGE BANDIT THREE ZERO ZERO DISTANCE FORTY."	"Take ranges and bearings, alternating between own blue fighter section and enemy aircraft group described. Report as rapidly as practicable."
"SEARCH FROM ZERO ZERO ZERO TO ONE FOUR FIVE."*	"Sweep search the sector 000°-145° true."

*Note: Always indicate sector in a clockwise direction.

7. Visual Communicatoin

Visual signals to combat, patrols are very slow and are practically useless when enemy aircraft are approaching the fleet. The short reliable range of most of our Radar warning sets requires immediate action as soon as enemy aircraft are detected approaching the fleet. Commander Air should always be allowed to break radio silence on the Fighter Net, if enemy aircraft in numbers are detected approaching the fleet.

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Also some latitude should be allowed ships in the distant screen using radio for an initial report of a number of enemy aircraft approaching the fleet, if the visual system is not considered sufficiently rapid. The promptness with which an initial report reaches Commander Air will often determine whether there is one or several sections of VF available to intercept the enemy, and mean the difference between, a successful and a missed interception.

8. Frequency of Radar Reports

No definite rule can be laid down for how often reports should be made. The governing consideration should be that communication circuits are not overloaded and that sufficient reports are made to insure proper plots being kept in other ships.

F. Radar Plot

1. Fundamental Considerations

(a) To exercise effective Radar control, and possibly Fighter control, a separate, adequately equipped Radar Plot is necessary.fe It is being provided for carriers. It is equally necessary for battleships, particularly flagships.

(b) Radar Plot is of little use unless the vital information can be instantly transmitted to it and rapidly and continuously disseminated to all gunnery control stations throughout the command as well as to the O.T.C. and F.D.O.

(c) Under present operating conditions almost any large ship may have to exercise Radar control a task force.

(d) Radar operators, particularly untrained men, must transmit their information,to a Radar Plot which can filter and interpret what the operator sees or thinks he sees. False contacts may prove almost as costly as failure to make contact. Either or both frequently happen, even with experienced operators as they become confused and do not remember what was or should be on a given bearing. Operators cannot be heckled or hurried into giving more information than is clearly apparent.

(e) Radar Plot must receive Information from many sources besides own Radar. Lookouts, OOD, signal bridge, etc., must keep Radar Plot up to the minute regarding the tactical situation at all times. Radio information from other ships acting as Radar guard for other sectors must be plotted. Every bit of information regarding location of own and enemy forces must be kept on Radar Plot all the time, particularly when the plot is kept by OTC or Radar control ship. During low visibility it is of the utmost importance to note position of own forces frequently. Often during actual maneuvers, the mid watch has reported an enemy contact which turns out to be own screen. Even experienced operators sometimes are unable to decide whether a Radar indication is a large ship, a small one or a cloud.

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(f) The officer in charge of Radar Plot and control has tremendous responsibility. He must be experienced in tactics as well as Radar.

(g) Repeated attempts to keep a complete Radar Plot in Flag Plot or Chart Bouse have been unsatisfactory for many reasons; interference, noise, confusion, delay, etc. Really successful operation has not been obtained with any installations so far used, except for short periods where everything else in Flag Plot and all maneuvering was stopped or restricted.

(h) Thus the proposed system illustrated on page 24 has been evolved and tested by actual operation.

(i) In disseminating and receiving information in Radar Plot, the loud speaker communication phone or voice call equipment (Donald Duck) is most essential. It is most needed during cruising conditions, prior to General Quarters. Quick reports and questions, direct from officer to officer, are essential to decide on action when a contact appears to be developing. Officers are too greatly restricted if they attempt to wear telephones indefinitely. Talkers are most unsatisfactory, particularly green men who must be used. At General Quarters, the interphones are backed up by sound powered phones, thus if the system goes out after commence firing, no confusion results. In a modern blitz, the most important communications are those required before commence firing. The fundamental tactical principle must be applied before commence firing; the first few salvos frequently determine the results of the action. Most ships are using inter phones of one type or another and all who are using them find them invaluable.

2. General Considerations

In view of the fact, that the foregoing provisions cannot be effect immediately in all the larger ships, the following general points are presented:

1. Radar plotting should be conducted by Radar Control (OTC), Fighter Director and their respective reliefs and all Radar Guard Ships.

2. In every ship some provision should be made for a standby Radar Plot. In one ship in addition to Main Radar Plot, plots are located in the chart house and Main Battery Plotting Room. These plots are kept on mooring boards by seamen.

   (c) In each ship Radar Control and Radar Plot should be located as close together as convenient and connected by the best communication facilities both electric and voice tube.

   (d) Where no separate location is provided for Radar Plot it should be maintained in the Flag Plot or Chart House.

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3. Radar Plot Procedure

(a) The Radar Plot should be in polar coordinates, origin at Fleet Center, radii in true bearings, distance in nautical miles.

(b) Since the Fleet Center is normally in motion, the relative movement plotting system should be used. With aircraft cruising speeds ten to fifteen times fleet speed, the relative plot will differ but little irom a navigational or geographical plot for aircraft work. In plotting surface ships with speeds on the order of one or two times fleet speed, the plot must be handled in relative movement to predict time and point of contact. The 20 mooring board (H.O. 2665) is considered the smallest satisfactory plotting sheet. It will be convenient to plot the fleet disposition to scale on a pivoted overlay which can be rotated with the fleet axis.

(c) For Fighter Direction, a special plotting board and plotting diagram has been prepared by the Fighter Director School, Norfolk. Samples have been shipped to each carrier. The board measures about 40 inches square and is adopted for use in a tilted position. Additional rolls of an improved plotting sheet are being printed by the Hydrographic Office.

(d) Time is the essence of successful Radar use. The development by every prospective Radar Control, Fighter Director, and Radar Guard Ship of standard plotting procedures to make the best use of available information is absolutely necessary. Dead time errors on the order on one minute are sufficient to cause a missed fighter interception, since aircraft moving in different directions at high speed may travel a relative distance greater than the range of visibility. Interceptors should be directed to a predicted meeting point.

4. Radar Plotting Aids

(a) Nomogram

Two scales are used on the mooring board; one of 2,000 yards to an inch and one of 10,000 yards to an inch. Points plotted on the latter scale are enclosed in a small circle to identify them. An alignment nomogram (as illustrated on page 26) engraved in a piece of cellulose acetate is employed to determine relative speed from the points plotted. The nomogram is placed over the plotted points and, depending upon the time interval elapsed, relative speed is read directly. The use of this device makes possible the determination of target course and speed within a few seconds after receipt of the second bearing and range on a target.

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[P A G E     M I S S I N G]

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(b) Peg Board

In one ship the Radar plotting officer transmits all contacts to the bridge over the JA phone and, as soon as a contact is developed gives the bridge the estimated course and speed of the target. This information is also simultaneously received by sky control. In addition, the sky control officer has a JS talker who keeps him informed of all contacts. This JS talker keeps pegs set in a peg board (illustrated on page 28) showing all aircraft in the vicinity. The director control officers are kept informed by the computer operators in Plot over the 1JP, 2JP, 3JP and 4JP phones. A large, blackboard showing the positions of all aircraft within 30,000 yardsis kept in Plot for the information of the computer operators.

5. Time-Bearing of Radar Plot

One form of Radar plot which has been used on the U.S.S. Nashville and found to be most effective and simple is the time bearing plot. When a Radar ship is operating its part of a convoy escort this form of plot should prove especiall helpful in keeping track of vessels of the escort and convoy during low visibility, thus enabling strange vessels to be recognized as such at once. The plot is illustrated on page 30.

(a) A 20 inch, or wider,yrollrpf/unlined paperis used. A ruler, which extends across the paper is fitted with a scale of degrees (10 degrees to ½ inch) marked from 180° at its left end to 360° (0°) at its center and then to 180°, again, at its right end. The gradations represent relative bearings.

(b) Whenever possible, the plot is established before low visibility sets in, so that friendly ships can be located amd identified. This is accomplished by means of telephone communication between an observer on the bridge and the plotter. A horizontal line is drawn with the ruler. The relative bearings of each ship, as observed by the Radar and confirmed by the bridge observer, is marked aiong the horizontal line, and the point thus determined is marked with the ship's name and Radar range.

(c) The horizontal line along which these data are recorded is marked at its left end with the local zone time when the sweep was commenced, and at its right end with the local zone time when ut was completed. The paper is then shifted upward and a new horizontal line is drawn at a convenient distance below the other. This is marked at its left end with the local zone time, and a new sweep is made, as before, after which the local zone time of completion is marked at its right end.

(d) An essential feature of the plot is the drawing in of vertical or nearly vertical lines connecting successive points of the same ship.

(e) Whenever the ship changes course, the Radar operator must be informed of the direction and amount and reminded that Radar bearings will shift to the other direction by the same amount.

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--30--

One difficulty, likely to be encountered even with technically perfect Radars, particularly when the convoy is large, results from the blanking off by large convoy vessels of outlying screening destroyers, which later become unblanked due to gradual changes in relative positions. The destroyers, thus suddenly appearing on the screen, are likely to be reported as strangers. The best safeguard against this is a carefully made initial sweep, during good visibility, so that cases where large ships are likely to blank off small ones can be recognized in advance. The Radar operator also requires a plan view of the whole disposition with ships in their prescribed positions for checking.

VII. OPERATIONAL USE OF RADAR AT SEA

A. Factors Affecting the Use of Radar at Sea

1. Danger of enemy interception of Radar transmissions and radio direction finder activity on same. The constant presence of this danger may necessitate the curtailment of own Radars transmissions to some extent.

2. Probability of attack by aircraft or of encountering enemy surface ships. This will depend upon:

1. Operation upon which own force is engaged.

2. Proximity of enemy air and/or naval bases.

3. Intelligence of enemy intent =ions dispositions or methods.

3. Visibility conditions defending on weather and time of day.

4. Maintenance of equipment. Shutdowns for routine maintenance work must be fitted in with the current operating requirements. Instrument life may be prolonged by relying on lookouts during good visibility.

5. Cognizance of the fact that the use of Radar enablea AA defense personnel to relax somewhat. This is considered to be of particular importance during the summer in northern waters where long hours of day ight prevail.

B. Counter Radio Direction Finder (RDF) Measures

As has been mentioned before, it is quite possible for the enemy to intercept our Radar transmissions. In addition it is possible for them to obtain bearings on our ships by means of radio direction finders. Although apparatus necessary for this purpose is probably installed at the majority of shore stations, it is believed unlikely that any but the largest enemy ships are so equipped. The danger of such enemy action cannot be entirely eliminated, but the risk can be reduced by the use of appropriate counter RDF measures. These are of the greatest importance and must be carried out carefully and intelligently if they are to be

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effective. Negligence in their use, even for a short time, is likely to compromise the position of our own units.

The general rule for counter RDF measures is to use the Radar transmitter for the shortest possible time consistent with a reasonably effective search. The antenna should be kept training at maximum speed when a target is not actually being investigated. In addition the search sector should be changed between each transmission when practicable.

No specific directions for counter RDF measures can be given, but Radar personnel should be allowed considerable latitude in working out effective measures.

C. Radar Watches

1. Warning

A warning watch should be kept continuouslyy to warn of enemy aircraft, and particularly during low visibility to warn against surface ships. The exact, nature of the warning watch will depend on the current situation.

(a) Transmitting Watch

(1) Using counter RDF measures. This is the type of warning watch which will be most generally used.

(2) Not using counter RDF measures. This type watch should be employed only when an attack is known to be imminent, or when it is obvious that the enemy is aware of our position.

(b) Receiving Watch

(1) There is some desirability of keeping a receiving watch with the Radar at all times when not transmitting, on the chance of intercepting enemy Radar transmissions. This may be done at ranges much greater than those at which it is possible to obtain echo signals and it is possible to take bearings on such intercepted signals. Unfortunately in cannot be predicted what form such Intercepted transmissions will take on the screen of the cathode ray tube, but it as possible to distinguish them audibly by a headset plugged Into the receiver.

(2) Use of Radar as Radio Direction Finder. It is feasible to employ Radars as radio direction finders. Accurate bearings and approximate ranges can be obtained In this manner. Search Radars from ideal instruments for tracking radio transmissions of like

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frequency, even though they receive no echo, at ranges up to 60,000 to 80,000 yards. The signal strength reaches a maximum when the antenna is trained on the bearing of the target. The use of the external sweep to stop the signal received is a great help in gaining accuracy when using the receiver as a radio direction finder. The bearing is thus determined accurately and an estimate of the range can be made by noting the height of the received signal and the sensitivity adjustment.

Although no information is available, it is thought possible to employ Radar as a radio direction finder when the enemy renders ordinary Radar operation ineffective by jamming. If the transmitter is secured and some means can be provided to use the incoming jamming signal as an external synchronization voltage for the oscilloscope, it should be possible to train the antenna to the bearing which gives maximum jamming signal strength and so to get a rough determination of the position of the enemy.

When an interception is made on a receiving watch, the operator should switch immediately to a transmitting watch, preferably using counter RDF measures. The chief advantage of the receiving watch is that it may be used even when, for purposes of security, it is not deemed wise to use the Radar transmitter.

(c) Combination Receiving and transmitting Watch

Under certain conditions this type of watch may be desirable. When it is ordered, the receiving portion should be carried out for as short a time as possible consistent with an all round search, and should not exceed two minutes. Otherwise flow flying aircraft or high speed surface craft may approach undetected.

2. Fighter Direction Watch

This watch should be kept in the Fighter Directing Ship at all times when a combat patrol is in the air or standing by on deck.

3. Standby Fighter Direction Watch

This watch should be kept by the standby fighter directing ship whenever a combat patrol is in the air.

4. Fire Control Watch

Fire Control Radar equipment is useless unless it is operated continuously (e.g. without using counter RDF measures), so it should be brought into operation only when it becomes absolutely necessary. On the other hand, if it is started up too late, its advantage of obtaining an early solution to the fire control problem and allowing own ship to fire first will be lost.

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Therefore very careful judgment must be exercised in determining the proper instant for bringing the fire control Radar into operation. Operators of this equipment must stand by with the antenna trained to the proper bearing, and fully prepared to start transmitting the instant the order is given. The operators should be taught that as soon as they detect a change in the normal rate of change of range to become particularly alert and send accurate ranges more often. This system has proved so successful in one ship that the graphic plotter operator can inform the fire control personnel almost immediately of changes in target course and the direction of such change. The solution of target course by rangekeepers is based largely on range rate determined by the Radars.

D. Radar Policies

1. Reasons for Establishing Radar Policies

A number of Radar policies for the employment of Radar should be established to fit the particular conditions under which units of the fleet may be operating. It is the duty of the O.T.C. to promulgate the appropriate policy to all Radar ships in the disposition, remembering it is desirable to have the fewest possible Radar equipments operating consistent with efficient and effective gathering of complete information. This will facilitate Radar communications, and reduce the possibility of enemy detection of our own Radar transmissions.

Each Radar policy should be assigned a designating letter or number and placed in effect by some order from O.T.C. such as "Employ Policy BAKER."

2. Possible Radar Policies

(a) Transmission may take place only when air or surface attack is imminent.

(b) Transmission may take place using counter RDF measures, shifting to continuous transmissions if an unidentified formation is detected closing the fleet within some specified distance.

(c) Carry out a sweep, employing counter RDF measures, every ten minutes, shifting to continuous transmissions as noted in (b).

(d) No restriction on transmission.

(e) Employ a combination transmitting and receiving watch.

(f) Revert to a receiving watch every fifteen minutes for the shortest time necessary for an all round sweep. This time is not to exceed 2 minutes, except when necessary to take a bearing. Then resume normal watch.

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VIII. OPERATIONAL USE OF RADAR IN HARBOR

Radar may be used in harbor for the following purposes:

Auxiliary Warning Apparatus

1. To provide distant warning in harbors where there is little or no warning organization on shore.

2. In other harbors to augment the shore warning organization.

3. For fire control purposes during attacks on a harbor.

B. Calibration

Several types of errors exist in all Radar sets, and it is of the greatest importance that an accurate calibration of each set be made frequently. This can be done best in harbor by ranging on prominent landmarks, such as lighthouses or water towers, the distances to which are known within 25 yards. To facilitate this procedure special targets are being constructed at some anchorages., The detailed instructions for carrying out a calibration are.contained in Ordnance Pamphlet ORD. 657

C. Training

It has been mentioned before that considerable operating experience is required before a Radar operator attains a high degree of proficiency. Therefore some sort of training program should be carried out by each ship when in harbor, where no Radar operating schools are located ashore. Any available planes may be used for tracking purposes, or the following scheme may be carried out. An ordinary meteorological balloon may be used as a target, by suspending below it ten dipoles of correct length for the frequency of the Radar set being used) arranged in the form of a ladder. The dipoles maybe constructed of thin metal strips (preferably aluminum), twisted so that the upward motion of the balloon will keep the assembly rotating continuously. This type of target is easily identified by the periodicity of the fading resulting from the rotation of the dipoles. This method should never be used when there is any change of the dipole ladder falling into the hands of the enemy, since from this they may determine the frequency of operation of some of our Radar equipment.

D. Security

Normally there should be no restriction on transmission or type of Radar transmission in harbors. Counter RDF measures may, however, be desirable at certain times.

1. At secret bases, or when it is particularly desired to conceal the fleet's return to harbor.

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2. When desired to simulate ships at sea.

3. For training purposes to familiarize operators with counter RDF measures.

IX. USE OF RADAR BY SUBMARINES

A. At the present time little or no experience has been gained in the use of submarine Radar equipment. The information contained in this section is, therefore, based on the results of preliminary tests of Models SD and SJ.

B. The Model SD Radar for submarines is merely an aircraft warning device, and as such employs a non directional antenna. This means that targets may be located only with respect to range. It is possible to operate the equipment and obtain ranges on aircraft when the submarine is submerged with the antenna projecting a few feet above the water. When the submarine is on the surface, planes may be detected up to about 15 miles, depending on their altitude. Planes below 750 feet may be . detected at around 5 miles when the submarine is on the surface, and at around 3 miles when it is submerged. Planes at greater altitudes may be detected at from 3 to 10 miles with the antenna only 5 feet out of water. In a few instances the SD has detected surface ships up to 10 miles, but as a general rule it will pick up only those surface ships which are fairly close.

C. The Model SJ Radar is designed to function as a detector of surface craft and a torpedo director for submarines. It employs a directive antenna which can be rotated through 360°. When perfected it is expected that it will be possible to detect DD's at 3 miles and BB's at 6 miles with a range accuracy of 25 yards and a bearing accuracy of ¼° (submarine on the surface). When submerged with the antenna only a few feet above the water, ranges will be shorter, but no definite information is available on this at the present time. It should be mentioned that production of the Model SJ Radar will not begin until some months after the publication of this pamphlet.

D. The data on these two types of equipment indicates that just before surfacing, the submarine should come close enough to the surface to expose both antennas. Remaining at that depth, an all round sweep of both air and sea can be made to determine if it is safe to surface without being discovered. The periscope will probably be equally effective for searching the surface except during poor visibility.

E. While lying on the surface a constant watch should be kept with both equipments. The SD will give sufficient warning of approaching planes so that a crash dive can be made to escape detection. Except at night or during periods of low visibility it is not likely that the SJ will give any earlier warning of approaching surface craft than will a good lookout and for this reason too much reliance should not be placed upon the Radar.

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F. It is not known how effective the SJ will be as a torpedo director, but it promises to have a definite advantage at times when it is desired to keep the echo ranging equipment silent. There remains, however, the somewhat doubtful risk of the Radar transmissions being intercepted by the target ship.

G. In general the same precautions will have to be observed for the use of these types of equipment as those already outlined for the sets installed in the larger ships.

H. As more information on the use of submarine Radar is obtained it will be included in subsequent revisions of this bulletin.

X. MISCELLANEOUS OPERATING NOTES

A. General

Operating experience shows that it is not likely that a destroyer can approach closer than 16,000 to 18,000 yards to a Radar equipped ship without being detected. This range is affected by the size of the search sector and rate of sweep. For example: if a single ship is searching the entire 360°, it will take from three to four minutes (possibly more) because of contacting ships in own force and checking their positions. If a destroyer were approaching the unit at a relative speed of 40 knots, in three minutes it would have closed nearly 4,000 yards and might well be within gun range of the screen before being detected. This is further argument for the practice of assigning search sectors to Radar Guard ships.

B. Sweeping

Sweeping should be carried out at the maximum speed consistent with efficiency and the requirements of the counter RDF measure being employed. The following is a rough guide for time of sweeping 360°, but the presence of land echoes will necessarily increase the time of sweep:

Time (in minutes) Required to Sweep 360°
	CXAM SC	FA, FC, FDM FH
Taking counter RDF measures	2	4
Not taking counter RDF measures	1	2

C. Radar Operator's Log

For each Radar set a log should be kept, recording the following:

1. Radar policy in effect at all times.

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2. Other general instructions given to Radar.

3. Time of commence and cease transmission.

4. All initial detections and final observations of a particular target. This is important in order that complete operating data may be obtained for each set to determine its capabilities and limitations under different conditions.

5. All observations of friendly or enemy Radar transmissions with bearings if possible.

6. All unusual observations made by means of the Radar receiver.

7. Irregularities in functioning of equipment, and action taken.

8. Name of operator and time of start and finish of watch.

XI. FIGHTER DIRECTION FROM AIRCRAFT CARRIERS

This section is based directly on the Tentative Doctrine for Fighter Direction from Aircraft Carriers, dated August 6, 1941. Additional information obtained from more recent experience has been included.

A. Object

The object of Fighter Direction is to provide a means whereby visual and Radar reports of enemy aircraft may be used to furnish fighters quickly and accurately with the information necessary to enable them to Intercept enemy aircraft

B. Policy

It is the policy to detect the enemy aircraft by Radar or by sighting, to correlate the information received from these sources at the fighter Directing Center of the Fighter Directing Ship, and then to pass the directions to the fighter patrol in the air.

C. Location of Fighter Directing Center in a Naval Force

1. Aircraft Carrier Available

The Fighter Directing Center of a naval force should be situated in an aircraft carrier, if one is available, for the following reasons:

1. A carrier will know best when fighters must land to refuel, the number of planes available for patrol, conditions of visibility in the upper air, and the other essential details of operating aircraft.

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2. A carrier is best able to tell the position of her own aircraft at any moment.

3. Fighter pilots have practice in communicating with carriers, and such communication will be more reliable than if any other ship, which happens to be operating with the force at the time, should undertake this duty.

4. The fighters may easily distinguish the carrier from other ships of the fleet. This enables them to judge their position relative to the directing ship with greater ease and speed.

2. No Carrier Available

If there is no carrier present in the naval force, a heavy ship, equipped with Radar and situated near the center of the force, should be the Fighter Directing Ship

3. Standby Fighter Directing Ship

When an air attack is expected by the fleet or force, there should be a standby Fighter Directing Organization in another ship equipped with Radar. The plot of air,operations should be kept up to date on this standby ship with all personnel and equipment ready to take over the duties of Fighter Direction. When VF are over the fleet, but no attack is expected, the Standby Fighter Directing Ship should be capable of taking over in about five minutes.

D. Fighter Direction Organization of a Carrier

Fighter Directing Officer (FDO)

The FDO should be stationed in the Fighter Directing Center which will hereafter be called "Radar Plot." Since the FDO must, himself transmit orders to the combat air patrol, his personality is of the greatest importance. He must supervise the work of the Fighter Directing Organization, including the Radar operators, in a manner which creates quiet and efficient operation. He must reach correct decisions rapidly, formulate his orders, and transmit them to the combat air patrol in a clear, incisive manner which will hold the complete confidence of the pilots.

2. Radar Plot

(a) Location

Radar Plot is the brain of the organization which protects the fleet or force from air attack. Consequently a suitable space will be provided for this activity, and the most efficient equipment for communication and plotting must be used. It is desirable that information contained in Radar Plot be readily and visibly available to the Commanding Officer and

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the Air Plot Officer. It is desirable that information contained in Radar Plot be readily and visibly available to the Commanding Officer and the Air Plot Officer. It is, therefore, necessary to locate Radar Plot physically contiguous to Air Plot with means of physically separating Radar Plot from this activity, but with facilities for easy access or visibility by interested control parties. In carriers special arrangements are being made to produce a satisfactorily located Radar Plot. For other ships, until more experience is gained, it will be necessary to use the chart house or some other space near the pilot house as a Radar Plot.

(b) Personnel

Fighter Direction requires quiet and complete freedom for the Fighter Directing personnel to concentrate upon the fast moving problem of plotting Radar information and translating it rapidly into precise orders to the Fighter Patrol. It is, therefore, mandatory to reduce Radar Plot personnel to the minimum for efficient operation, particularly with respect to telephone talkers.

3. Sources of Information

The FDO will generally receive his, information from:

1. The Radar operator or operators.

2. Other Radar ships by visual or radio. A radio receiver and operator on the internship warning net should be placed near him for this purpose.

3. Reports of enemy aircraft sighted by lookouts in the ship. A voice tube or telephone to the lookout station is necessary for this.

4. Communications

Communication doctrine and organization of a naval force should provide means for all Radar ships present to pass reports of aircraft detected to the Fighter Directing Ship. The reports should be made by visual until the presence of the fleet is likely to be discovered by the enemy aircraft, in order that radio silence may be preserved. In case interception of enemy aircraft becomes essential, the extra speed given by radio reporting becomes an important factor in deciding the value of radio silence.

E. Operations in Radar Plot

1. Probable Personnel Requirements

1. Fighter Directing Officer (FDO).

2. Plotting Officers.

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3. Three radiomen to monitor two voice channels between the FDO and the Combat Air Patrol, and the one inter ship warning net. The FDC should himself transmit orders to the combat air patrol by means of an auxiliary microphone located conveniently to his normal position.

4. One or two talkers as required for communication with pilot house, air defense, main battery control, air plot, etc. It is considered that two talkers is the maximum acceptable for Radar Plot, and one is preferable.

5. Recorder. An electric voice recorder will be supplied to each Radar Plot in the near future, but this will not replace the recorder whose duties will include keeping the information boards up to date.

Probable Equipment Requirements

1. Facilities for positive and rapid communication with Radar operator.

2. Three remote control operating positions far remote control of transmitters for combat patrol and the transmitter on the inter ship warning net. If practicable, it is desirable that the radio operators be provided with selector switches for remotely controlling the power output and type of emission of Combat Air Patrol transmitter.

3. Three receivers.

4. The telephone circuits in Radar Plot should be reduced as much as practicable by the use of selective switches and common circuits in order to limit the number of talkers to a maximum of two. Since air and Radar Plots will always be adjacent, the telephone circuit facilities of Air Plot may in some cases suffice.

5. Selective switches with handset and headset with selections for the following circuits: JA, 1VG, 2JG, JL, 5JP, JS, JX.

6. Ship's service telephone (Executive cut in).

7. Door and scuttle to Radar Control Room.

8. Door or hatch and/or viewing screen to Air Plot, Pilot House (or chart house) and the Flag Plot.

9. Plotting boards of generous size and adapted to clear representation of the movements of several groups of aircraft. Provisions for height indication is desirable. (One experimental portable plotting board has been supplied to each CV).

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10. Blackboard showing fighter patrols in the air, call signs, time of departure, availability of fighters on deck, etc.

11. Bearing indicators (circuits GT, 2PD, 2PE, 2PS, and 2PM) as found necessary after further study of the problem.

12. One train indicator to indicate Radar antenna train. It will be desirable to combine this with a gyro repeater.

3. Miscellaneous Notes

1. Since Radar detects aircraft as an instantaneous present bearing and range on a screen, and does not produce a continuous record showing course and speed, and indications cannot be used immediately as direction to fighters. It is necessary at present to predict manually a future position of the enemy which the fighters may be directed to intercept; in other words it is necessary to forecast enemy movements.

2. A convenient method of keeping the Radar plot is to use a mooring board covered with a piece of celluloid, and a "chinagraph" pencil; or by a special board with tracing paper over the plotting sheets. The second method provides a record of the operation which is of value in analyzing the operations.

3. It is important that the fighters be relieved of the details of navigation in carrying out the interception so that they may be free to concentrate on looking out for the enemy planes, and be ready to engage them. To accomplish this the FDO should transmit to the pilot magnetic courses to steer, and indicated speeds at which to fly. Generally, however, unless the FDO has very exact information of the existing cloud conditions, he should inform the fighters of the enemy's altitude, rather than specify the altitude for the fighters.

4. The Radar reports will be received as a series of bearings and ranges relative to the reporting ship, so that the FDO will be presented with a relative rather than a geographical picture. Since both the friendly and enemy planes are reported through the same medium, the FDO is concerned only with their relative positions in directing the fighters to an interception. Thus, the wind and own ship's course and speed need not be applied to the courses and speeds transmitted, and corrections to the fighter's courses will result from the relative motion of the opposing planes as indicated by the subsequent Radar reports. A separate geographical plot may be maintained, but generally this is slower and of less value to the FDO in directing the interception.

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5. When Radar reports are not available, as in the case of low flying shadowers, it is very desirable that both types of planes be reported through the same medium so that a relative plot may be kept. If this is not possible, it will be necessary for the FDO to use any information available, and may even require that the fighters be directed to positions relative to the carrier or other ships, to circle, or to search relative sectors.

F. Visual Communication with Planes

1. During radio silence or in the event of casualty to radio equipment it is possible to communicate by flashing light with fighters over head. This method of communication cannot be used if the fighters are above 5,000 feet, and in any case it is very slow. This system is considered too impractical for use except as a last resort, but training should be conducted in order to make it as effective as possible.

2. It has been suggested that the guns of the fleet be trained on the bearing of the enemy planes as a visual signal, but the British have found that the fighters do not see this signal, even though the gun barrels are covered with white paint to give them prominence.

3. Bursts of anti-aircraft gunfire give a good indication of position if they can be placed near the enemy planes, but do not help if they are fired while the enemy is still out of range, as they fall very short of the target and are apt to mislead the fighter patrol who cannot easily visualize the line of fire.

G. Notes on the Use of Radar Directed Fighters for the Protection of a Naval Force

1. The number of fighters to be sent on patrol depends on the total number of aircraft available to maintain patrol throughout the day, and on the likelihood of attack during the period of each patrol.

2. Patrol is maintained over the force to be protected at a height close to that at which enemy planes may be expected to fly, depending on the existing cloud conditions.

3. The patrol should remain immediately above the fleet unless there is good reason to expect an attack from a particular direction, in which case the patrol may be stationed, up to 15 minutes from the fleet in that direction, but not outside the visible range. The fighters may patrol up sun of the fleet if shadowing aircraft are expected, or they may make frequent sweeps in the direction of the sun.

4. Low flying shadowers may not be detected by ship control Radars. However, large flying boats at low altitudes can be detected by fire control or ship detection Radars better than by most aircraft detection

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sets, since a plane at low altitude is essentially the same as a tall ship as far as Radar is concerned. An FC set will consistently detect a low flying patrol plane of medium size up to 18,000 yards.

Large flying boats have been used recently to shadow from astern or "up sun", keeping below the horizon out of sight of the fleet, periodically closing to maintain contact and gather information of fleet movements. These shadowers have usually been sighted by ships of the fleet or by fleet aircraft flying in the vicinity. The position of the enemy is passed to the fighter patrol, but it is difficult for them to intercept because all touch with the enemy is lost as soon as he retires out of sighting distance over the horizon. Aircraft shadowing from high up are more easily dealt with, because they are at sufficient height to be detected by Radar at greater distances. In the case of low shadowers it is not good policy to call down the high patrol to intercept them. Instead it is better to fly off fresh VF from the carrier. It is of the utmost importance that shadowers be destroyed or permanently driven off. Even after it has appeared that the enemy planes have sighted the fleet and reported its location, it is urgent that these shadowing planes be prevented from disclosing further movements of the force to be protected.

5. Recent wartime practice of most aircraft attacking a fleet has been to close the fleet upon a steady course until it is sighted and then to circle just beyond the visible range so as to attack from the direction of the sun. This maneuver, if carried out at high speed, also has the effect of circling round the defending fighters and so evading them. With the use of Radar it should be possible to direct the fighter patrol to thwart this maneuver. At all times, great care must be taken to keep the fighters interposed between the attack and the fleet.

6. If the enemy has approached so close to the fleet that he cannot make a large detour to avoid the fighters without disorganizing his attack, the fighters may be given a position at which to intercept him; it is desirable that the interception should occur when the enemy is between 20 and 25 miles from the fleet.

7. When a unit of the Combat Air Patrol makes a visual contact with an enemy unit the Fighter Directing Ship should cease directing that unit in order that the officer in command of the Combat Air Patrol unit may have complete freedom to maneuver his unit. Upon completion of an attack, the FDO should be prepared to give immediate instructions as to the course to steer to return to the carrier, if it is requested, or if it is apparent that the patrol is not returning expeditiously.

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8. In the absence of Radar identification or recognition equipment it is desirable to confine own air activity to a minimum to avoid the confusion which results from a multiplicity of unidentified Radar contacts. It is possible that aerial pickets and Intermediate Air Patrol do more harm than good and may have to be eliminated. Combat patrols may be employed more efficiently if kept alerted on the deck of the carrier instead of in the air, if the combination of Radar range and fighter performance make interception possible at a satisfactory distance from the fleet; in addition movements of friendly planes (such as sector searches, arrivals and departures of attack flight, etc.) should be furnished by the Fighter Directing Officer to the Radar Control Officer.

9. It will be necessary to alter the tactics of our own planes on search and tracking missions. An alert enemy equipped with Radar will observe every plane which is above the horizon at any range. Searching and tracking planes should be made aware of this fact. It is possible that through judicious use of extremely low altitudes and radical changes of position when below the horizon, present day planes themselves may escape being tracked and attacked.

XII. CONCLUSION

It should be appreciated that Radar equipment is continuously undergoing further improvement and that the knowledge of its use is still limited. Officers and men associated with it should, therefore, feel that they have some latitude in exploiting its use, and the contents of this bulletin should be regarded as a guide and a basis for improvement after further experience afloat.

Suggestions for changes which will lead to improvement in Radar Bulletin Number 1 will be welcomed.

 

See Radar Bulletin No. 1A: Capabilities and Limitations of Shipborne Radar for the end-of-war (July 1945) evolution of this doctrine. --HyperWar

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