antiaircraft searchlight units ~ 1940

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    MHICopy 3 FM 4-115LIe' t. Ciioaelf, Inlit

    WAR DEPARTMENT

    COAST ARTILLERYFIELD MANUAL

    ANTIAIRCRAFT ARTILLERYOPERATION OF MATERIEL

    AND EMPLOYMENT OF PERSONNEL,ANTIAIRCRAFT SEARCHLIGHT UNITS

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    FM 4-115

    COAST ARTILLERYFIELD MANUAL

    ANTIAIRCRAFT ARTILLERYOPERATION OF MATERIEL

    AND EMPLOYMENT OF PERSONNEL,ANTIAIRCRAFT SEARCHLIGHT UNITS

    PREPARED UNDER DIRECTION OF THECHIEF OF COAST ARTILLERY

    UNITED STATESGOVERNMENT PRINTING OFFICE

    WASHINGTON: 1940

    For sale by the Superintendent of Doclunents. Washington. D.C. - Price 35 centp

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    WAR DEPARTMENT,WASHINGTON, June 20, 1940.

    FM 4-115, Coast Artillery Field Manual, Antiaircraft Ar-tillery, Operation of Mat6riel and Employment of Personnel,Antiaircraft Searchlight Units, is published for the informa-tion and guidance of all concerned.[A. G. 062.11 (5-1-40).]

    BY ORDER OF THE SECRETARY OF WAR:G. C. MARSHALL,

    Chief of Staff.OFFICIAL:

    E. S. ADAMS,Major General,

    The Adjutant General.

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    TABLE OF CONTENTSParagraphs PageCHAPTER 1. GENERAL.Section I. General______---------.-- ------ 1- 5 1II. Aerial sound ranging ------ _____ 6-12 3

    CHAPTER 2. TRAINING.Section I. General -------------------------- 13-17 7II. Selection of personnel ____________ 18-23 8III. Individual training_---____-- ____ 24-31 11IV. Section training_________________-32-41 16V. Platoon training -_________________ 42-52 22CHAPTER 3. OPERATION AND FUNCTIONING OFMATtRIEL.Section I. Sound location equipment_________ 53-58 29II. Control station -______-___________ 59-61 38III. Searchlight ---. _____ ___- __-__---_ 62-67 42IV. Power plant__----__--- ___________ 68-72 46V. Vehicles _________________________ 73-77 48CHAPTER 4. PREPARATIONS FOR ACTION AND FORMOVEMENT.Section I. Preparing for action _--___________ 78-94 55II. Orienting and synchronizing -_____ 95-99 75III. Preparing for the road___________ 100-108 80IV. Protective measures_-___________ 109-111 83CHAPTER 5. ORGANIZATION.Section I. Searchlight battery______________ 112-113 85

    II. Searchlight platoon _____________ 114-115 85III. Searchlight section __________16-117 86CHAPTER 6. SERVICE OF THE PIECE.Section I. Searchlight platoon action___-___ 118-126 90II. Duties of personnel __-__________ 127-129 92III. Drill of searchlight section______ 130-143 93IV. Notes on service of the piece_____ 144-151 104CHAPTER 7. MAINTENANCE _________-____________ 152-163 107CHAPTER 8. DRIL TABLE-_______-_______________________ 120APPENDIX. LIST OF REFERENCE:--------__________________ 121INDEX -----------_ - -_-_ ___-_- _- ------__-_-__ ____-__ - 123

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    FM 4-115

    COAST ARTILLERY FIELD MANUALANTIAIRCRAFT ARTILLERY

    OPERATION OF MATtRIEL AND EMPLOYMENT OFPERSONNEL, ANTIAIRCRAFT SEARCHLIGHT UNITS(The matter contained herein supersedes chapter 3 and sectionII, of chapter 5, part two; and Table 0, chapter 2, part three,Coast Artillery Field Manual, vol. II, February 1, 1933.)

    CHAPTER 1GENERAL ParagraphsSECTION I. General ___________- __.__._______________ 1-5II. Aerial sound ranging ----------__ _________-__- 6-12SECTION I

    GENERAL* 1. SCOPE.-This manual is designed for use by antiaircraftsearchlight batteries as a guide in the handling of mat6riel,selection of personnel, employment of practical trainingmethods, and service of the piece. Drills and instructionsgiven pertain especially to the later types of materiel, butmay be applied with slight modification to all materiel ofsearchlight units, MVI, M1934, M1937, M1939, and M1940.* 2. REFERENCES.-This manual should be studied in con-junction with the references listed in the Appendix.* 3. GENERAL PROBLEM.-The ability of the antiaircraft artil-lery gun (and in some cases the automatic weapon) batteryto fire effectively on targets at night is dependent uponartificial illumination of the target so that continuouslypointed fire may be used. This artificial illumination isfurnished by searchlights.* 4. POSITION FINDING.-a. The presence of the target isdisclosed by the sound of its motors, propellers, and itsmovement through the air. While the sound, when withinthe hearing of the unaided ear, will give a general idea of

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    4 COAST ARTILLERY FIELD MANUALits apparent direction, this is not sufficient for the pointingof the searchlight because of the inherent directional inac-curacy of the human ear. The apparent source of the soundis constantly moving, and the sound itself is subject to a lagbecause of the time necessary for the sound wave to travelfrom its source to the point of reception. It is advisable, inorder that the light may be pointed properly, that the soundbe detected at the greatest possible distance, that the targetbe followed by its sound, that corrections for sound lag andother effects be applied, and that a prediction be made ofthe true position of the target. Where the searchlight andthe sound locator are so connected together electrically thatthe searchlight may be moved with the sound locator inazimuth and elevation, prediction may be continuous andautomatic. Aerial sound ranging is the process of locatingthe aircraft by means of the sound emitted. Aerial soundranging is used primarily at night to assist searchlights inlocating targets in order that they may be illuminated withthe minimum delay.The position of the target is determined when the azimuth,angular height, and slant range are known. For searchlightdirection, azimuth and angular height only are needed.b. Any system of position finding and target illuminationat night by means of sound location and searchlight illumi-nation should-(1) Determine with the greatest possible accuracy theangular height and azimuth of the apparent source of thesound.(2) Determine the effect of sound lag on azimuth and ele-vation so that the appropriate corrections may be applied.(3) Evaluate and apply corrections for the deviating ef-fects on the sound wave of other known causes.

    (4) Determine and apply corrections for parallax at thetarget, due to distance between searchlight and soundlocator.(5) Apply the corrections continuously and without anyloss of time.(6) Transmit automatically and continuously to thesearchlight the corrected sound locator data.2

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    ANTIAIRCRAFT SEARCHLIGHT UNITS 4-7(7) Move the searchlight continuously in azimuth andangular height so asgto follow the moving point source ofthe sound.c. The present standard system of target location andillumination embodies means for accomplishing all exceptitem (3) of the requirements indicated in b above. Nosatisfactory correction device has been developed for deter-mining and applying corrections for the deviating effects onthe sound wave caused by atmospheric conditions.d. The method of position finding by sound location isdiscussed in connection with the sound locator and acousticcorrector in paragraphs 7 and 26.

    * 5. EQUIPMENT.--a. The complete system for the detection,location, and illumination of aerial targets includes the fol-lowing equipment, the arrangement of which is shown sche-matically in figure 190:(1) Searchlight.(2) Power unit.(3) Sound locator.(4) Acoustic corrector (on sound locator).(5) Control station.b. When properly disposed in the field the searchlight is200 feet from the power unit, the control station is 500 feetbeyond the light, and the sound locator is 900 feet from the

    light. The connecting cables between each element areshown in figure 190, as follows:(1) Power cables from power unit to searchlight.(2) Data transmission cable to searchlight from soundlocator.(3) Distant electric control cable from searchlight tocontrol station.SECTION II

    AERIAL SOUND RANGING* 6. GENERAL.-See paragraph 4 for a general discussion ofthe position-finding problem.* 7. SOUND LOCATION.-Sound locators are designed to ac-centuate and make use of the ability of a person to deter-

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    7-9 COAST ARTILLERY FIELD MANUALmine the direction of a sound source by means of the binauralsense. When a man stands in the open where he is notbothered by echoes, he can determine by his sense of hear-ing alone the approximate direction of the source of a sound.He does this instinctively by turning his head so that he willface the apparent source of the sound. This is largely ac-counted for by the fact that the human ears are separatedby about 51/2 inches; hence any sound, unless originating inthe perpendicular plane bisecting the line joining the twoears, will arrive at one ear before it does at the other. Thehuman ear is sufficiently sensitive to detect this time dif-ference, and the listener's binaural sense tells him that thesound originated on the side which the sound first reached.It is to make the sound arrive at both ears at the sametime (and thus eliminate the time difference) that the headis instinctively turned until the sound is faced. When thesound locator is used, the sound source usually appears tothe listener to be directly in rear of his head when the hornsare pointed toward the source. 8. SOUND DISTURBANEs.-Sound travels through the at-mosphere, and the sound waves are affected by everychange and departure from uniformity in the transmittingmedium. The atmosphere itself is always in motion. Any-thing such as wind, density, or temperature changes whichcause the sound wave to drift or bend will produce an errorin the determination of the directi