United States Fleet Anti-Submarine Instructions

Part II - Aircraft

2000 GENERAL 2-1 -- 2-3
  2010 Mission 2-1
  2020 Air Control 2-1
  2030 Operational Readiness 2-1
  2040 Dissemination of Information 2-1
    2041 Pre-Flight Briefing 2-1
    2042 Periodical Examination 2-1
    2043 Study of Intelligence Data 2-1
    2044 Post-Flight Interrogation 2-1
  2050 Aircraft Commander's Responsibilities 2-2
    2051 Pre-Flight Inspection 2-1
    2052 Operational Equipment Flight Test 2-1
    2053 Arming Check Off 2-1
  2060 Training Centralized 2-2
    2061 Squadron Training as a Unit 2-1
    2062 Crew Training in Teamwork 2-1
    2063 Standardized Training 2-1
  2070 Photographs and Magnetic Wire Recorders 2-2
    2071 Photographs of Attacks 2-2
    2072 Photographs of Suspicious Vessels 2-2
    2073 Photographs and Negatives 2-2
    2074 Magnetic Wire Recordings 2-2
    2075 Completion of Action Reports - ASW-6 (Revised 7-11-44) 2-2
    2076 Forwarding of Action Reports - ASW-6 (Revised 7-11-44) 2-3
  2110 Search Tactics Non-Stereotyped 2-3
    2111 Tactical Considerations of Search 2-3
    2112 Rules for Visual Search 2-3
    2113 Visual Search for Schnorchel 2-3
    2114 Aircraft Radar Search 2-3
  2120 Lookout Bills 2-3
  2130 Search Overlap 2-3
2200 AERIAL SEARCH PLANS 2-3 -- 2-14
  2210 Planning the Search 2-3
  2220 Defining Effective Visibility 2-3
  2230 Determining Effective Visibility 2-4
    2231 Effective Visibility for Radar Search 2-4
    2232 Effective Visibility Explained 2-4
  2240 Selection of Plan 2-4
    2241 Searching for Schnorchel 2-4
  2250 Use of Nomographs 2-4a
  2260 Precautions in Copying Nomographs 2-4a
    2261 Effective Visibility for Visual Search 2-5
    2262 Aircraft Search Plan No. 1 Nomograph No. 1 2-6
    2263 Aircraft Search Plan No. 2 Nomograph No. 2 2-8
    2264 Aircraft Search Plan No. 3 2-10
    2265 Aircraft Search Plan No. 3A 2-11
    2266 Nomograph No. 3 2-12
  2270 A/S Barrier Patrols by Aircraft 2-13
    2271 Barrier Patrol Defined 2-13
    2272 Conditions Affecting Barrier Design 2-13
    2273 Basic Barrier Patrol 2-13
    2274 Successive Barrier Patrol 2-13
    2275 Probability of Contact 2-13
    2276 Multiplane Barrier Patrol 2-14
    2277 Symmetrical Barrier Patrol 2-14
2300 ATTACK 2-15 -- 2-19
  2310 Direct Approach 2-15
  2320 Strafing 2-15
  2330 Tactics Against Submarines That Fight Back 2-15
    2331 Use of Guns in Attacks 2-15
    2332 Delaying Attack to Await Support 2-15
    2333 Coordinated Attack 2-15
  2340 Depth Bomb Attacks 2-15
    2341 Target Angle and Release 2-15


Table of Contents--Part II (Continued)

    2342 Point of Aim 2-15
    2343 Attack Diagram 2-16
    2344 Diving Times and Turning Circles 2-16
    2345 Lethal Range of TNT and Torpex 2-17
    2346 Depth Bomb Table 2-17
    2347 Impact Spacing Curves 2-18
    2348 Number of Bombs Carried 2-18
    2349 Number of Bombs to Drop 2-18
  2410 Contact and Amplifying Reports 2-19
  2420 Calculating Rate of Approach 2-19
  2430 Gambit Tactics 2-19
    2431 Trapping Square and Continuous Gambit 2-19
    2433 Assumed Speed for Submarine Positions 2-19
  2440 Submarine Surrender 2-19
  2450 Neutral Ship at Scene of Action 2-19
2500 NIGHT ILLUMINATION 2-19 -- 2-23
  2510 Illumination of Friendly Vessels 2-19
  2520 Coordination of Crew in Night Attack 2-19
  2530 Searchlight Attack 2-20
    2531 Search Altitude 2-20
    2532 Radar Contact 2-20
    2533 Searchlight Contact 2-20
    2534 Shift to Visual for Attack 2-20
  2540 Flare Attacks 2-20
    2541 Release Position 2-20
    2542 Types and Delays 2-20
    2543 Search Altitude 2-20
    2544 Contact and Approach 2-20
    2545 90-Second Delay Flare Attack Diagram 2-21
    2546 120-Second Delay Flare Attack Diagram 2-22
    2547 300-Foot Delayed Ignition Flare Attack Diagram 2-23
2600 AIRSHIPS 2-24
  2610 Applicability of A/S Instructions 2-24
  2620 Attacks 2-24
    2621 Day 2-24
    2622 Night 2-24
    2623 Submarine Long Submerged 2-24
    2624 MAD Attack 2-24
    2625 Submerged Contact 2-24
  2630 Hydrostatic Fuze Settings 2-24
2700 RADIO SONO-BUOYS 2-24 -- 2-26b
  2710 Expendable Radio Sono-Buoys 2-24
    2711 Uses of Sono-Buoys 2-25
    2712 Orientation 2-25
    2713 Laying Full Pattern 2-25
    2714 Indoctrination Required 2-25
    2715 Gambit with Sono-Buoys 2-25
    2716 Gambit Operations 2-25
    2717 Sono-Buoy Pattern for Visual Contact 2-25
    2718 Sono Buoy Pattern for Gambit 2-26
    2719 Sono-Buoy Pattern for a Suspicious Surface Indication 2-26
  2720 S/B Magnetic Wire Recorder 2-26
    2721 Intermittent Recording 2-26
    2722 Recordings of Attack 2-26
  2730 Large Sono-Buoy Pattern 2-26
    2731 When to Use 2-26
    2732 Procedure for Laying 2-26
  2740 Tracking with Sono-Buoys 2-26a
    2741 Care in Using Same Color Sono-Buoys 2-26b
    2742 Interpreting Sono-Buoy Sounds 2-26b
  2750 Average Sono-Buoy Detection Ranges 2-26b
  2810 Effectiveness of Rockets 2-26c
    2811 Rocket Fire to Sink Submarine 2-26c
    2812 Rocket and Depth Bomb Attack 2-26c
    2813 Machine Gun and Rocket Attack 2-26c
  2820 Target Angle 2-26c
  2830 Glide Angle 2-26c
  2840 Point of Impact 2-26c
  2910 Definition 2-27
  2920 MAD in A/S Operations 2-27
    2921 Barrier Patrols 2-27
    2922 Investigation of Suspicious Areas 2-27
    2923 Trapping and Tracking Defined 2-27
  2930 Heavier than Air Tactics 2-27
    2931 Visual and Radar Contacts 2-27
    2932 Trapping Circle 2-27
    2933 Trapping Procedure from Trapping Circle 2-28
    2934 Tracking Pattern 2-28
  2940 Lighter than Air Tactics 2-29
    2941 Approach Speed 2-29
    2942 Trapping Procedure 2-29
    2943 Conditional Trapping Procedure 2-29
    2944 Procedure After Long Submergence 2-29
    2945 Tracking Procedure 2-29


United States Fleet Anti-Submarine Instructions

Part II



  1. The mission of anti-submarine aircraft is to seek out and destroy enemy submarines by the employment of the most effective methods of search and attack, and to provide aerial coverage to shipping.

  1. Insofar as practicable all anti-submarine aerial units shall operate under a uniform system of Air Control. The size of the control organization and details of its operation shall be prescribed by Fleet Air Wing Commanders in accordance with the requirements of the local situation.

  1. The Air Force Commander charged with the responsibility of training of A/S squadrons shall promulgate standards of training and readiness necessary to insure a satisfactory state of operational readiness.

  1. Dissemination of operational information shall be provided for pilots and air crews in the following manner:
    1. Pilots and air crews shall be briefed prior to take-offs on each operational mission, and supplied with any information in written form as necessary, to ensure that they are cognizant of:
      1. Prevailing and anticipated weather conditions affecting the operation.
      2. Recognition signals.
      3. Encoded calls and radio frequencies.
      4. Positions and descriptions of friendly units likely to be encountered.
      5. Friendly submarine BOMBING RESTRICTIONS and SANCTUARIES.
      6. Gun firing from shore batteries.
      7. Latest information on enemy forces.

    2. Periodically, examinations shall be held to insure that pilots and air crews remain conversant with:
      1. Current escort, patrol, sighting, and attack doctrine.
      2. Current communications plans.
      3. Procedure for proper handling of action reports.
      4. Identification of friendly and enemy aircraft and Men-of-War.
      5. Tactical employment of special equipment.
      6. Flight plan procedures and navigational aids.

    3. Pilots and air crews shall have access to such bulletins, action reports, charts, photographs, situation maps, mission boards and all other material that will assist them in carrying out their missions successfully.
    4. Immediately upon the completion of each operational flight the pilot and air crew shall be interrogated. A complete and accurate report of the events of the flight shall be made by the pilot and submitted to the commander in operational control.


  1. The Aircraft Commander
    1. Prior to take-off insure that his aircraft is properly fueled, armed, and equipped for the assigned mission.
    2. Immediately after take-off, conditions permitting, all radio and radar equipments shall be tested to insure that they are functioning properly. A short burst shall be fired from all guns to insure that they are in working order. If faulty operation of any of the above equipment is noted sufficient to prevent the successful execution of the mission, the aircraft shall report ad return immediately to base.
    3. After take-off and as soon as safety permits bombs shall be armed and all preparations made for immediate attack.

  1. Training shall, if practicable, be centralized in a single office functioning specifically as an operational control center for training purposes under a designated training officer. Personnel undergoing training shall be carefully instructed and briefed prior to undertaking any training flight, and upon completion of the flight they shall be individually interrogated and the results of the flight carefully analyzed. Accurate and complete records shall be maintained at all times. The following considerations shall be observed:
    1. Whenever practicable, squadrons shall receive anti-submarine training as a unit.
    2. The necessity for the entire aircraft crew to act as a well-drilled team shall be emphasized.
    3. Training methods and procedures shall be standardized.

  1. Photographs and magnetic wire recordings together with action reports shall be submitted after each anti-submarine attack. Every effort shall be made during fights to photograph all objects of military importance.
    1. As many photographs as possible of submarine attacks shall be taken to assist in the accurate determination of damage resulting from the attack and to indicate errors in approach and attack technique. Particular effort shall be made to photograph the approach, bomb impact, position of depth bomb explosion in relation to swirl, reappearance of submarine, final submergence of submarine, any debris, oil slick or survivors.
    2. At least two exposures shall be made of any unidentified or suspicious ship including a silhouette and a 45° angle shot. Additional exposures for close-up detail, such as camouflage, large boats on deck, extra guns mounted, etc., may be made at the discretion of the pilot.
    3. The negatives of all action photographs and a rough track chart of the action, showing the positions from which the various pictures were taken shall be forwarded to Headquarters, Commander in Chief, United States Fleet, direct. Motion pictures exposed during such action shall be forwarded UNPROCESSED. Upon the receipt of unprocessed motion picture film, it will be processed and a print sent direct to the submitting unit at the earliest practicable date. Photographs submitted with reports shall be accompanied by brief description so that nothing of interest or value contained in the pictures will be overlooked.
    4. Magnetic wire recordings together with log extracts of data necessary to correlate surface craft positions with times of recorded sounds shall be forwarded to the Commander in Chief, United States Fleet, after preliminary screenings by the Fleet Evaluation Center.
    5. The action report form, Report of Anti-Submarine Action by Aircraft - ASW-6 (Revised 7-11-44), shall be completely filled out and submitted for every attack or attempted attack using a weapon potentially lethal to a submarine. It shall contain the comments of the unit or squadron commander.


    1. One copy of the report form Report of Anti-Submarine Action by Aircraft ASW-6 (Revised 7-11-44), shall be submitted direct, by the most expeditious practical method, to the Headquarters, Commander in Chief, United States Fleet. Fleet, Force or Frontier Commanders may require additional copies of the above as desired.



  1. Search tactics shall not become stereotyped. Necessity for constant study of how to outwit the enemy and achieve surprise shall be impressed upon every pilot.
    1. Fullest consideration shall be given to the following factors in planning and conducting a search.
      1. Weather and cloud conditions.
      2. Altitude of the sun.
      3. Type and camouflage of aircraft.
      4. Characteristics of own and enemy special detection equipment.
      5. Possibility of enemy aircraft opposition.
      6. Type of illumination equipment carried.

    2. For visual search for surfaced submarines, use the following general rules:
      1. No clouds or clouds above 5000 feet, fly at 5000 feet.
      2. Scattered clouds with less than 5/10 coverage, fly in or just above (but not above 5000 feet). When the vertical development of the clouds limits the horizontal visibility fly as in "c".
      3. Scattered clouds with more than 5/10 coverage, or solid overcast below 5000 feet, fly below, hemstitching base of clouds.

    3. For visual search for Schnorchel, fly at about 1000 feet.
    4. Aircraft radar equipment shall be operated in accordance with the latest effective instructions issued by Commander in Chief, United States Fleet.

  1. Lookout watch bills designed to insure the maximum vigilance and most efficient search shall be provided for each aircraft. In areas where danger of enemy aircraft opposition exists, the lookout watch bills shall be designed to permit adequate air search with a minimum limitation upon the extent of the surface search. Provisions for frequent relief of the watches shall be provided.

  1. In planning a search, radar or visual, suitable overlap must be provided for adjacent sweeps as targets near the extremities of the detection range will be in the search area or swept path for only a fleeting instant and may, therefore, be missed.



  1. This section presents a set of basic search plans designed to meet the fundamental search situations which may be met by aircraft whose primary mission is anti-submarine patrol. The plans are general rather than specific, and are designed primarily for the use of officers responsible for planning operational flying. From these general plans, and the quantitative information presented with them, detailed plans can be laid out for particular situations.

  1. These plans take into account the established fact that no search plan can be completely sure of success. Any given plan has a certain chance of success which depends upon the layout of the plan and the ability to detect, which in turn depends upon the visibility or radar range, the patrol altitude, and the nature of the search. As a measure of this ability to detect, a quantity known as the


    effective visibility (expressed in miles) has been introduced. This may be thought of as a distance such that if the aircraft passed within this distance of the object of search the probability of sighting the object is high; while if the aircraft passes the object of search at a greater distance, the probability of detection is relatively low.

  1. Before any of these search plans can be used, it is first necessary to determine the effective visibility E. For Radar Search the effective visibility is given in Table 1 (Article 2231). Effective visibility for visual search is dependent upon meteorological visibilities, altitudes of flight, and types of targets and is shown in Table 2 (Article 2261). For any stated meteorological visibility only the altitudes for which values of E are given in the table should be used in search.
    1. Table 1 - Effective visibility for Radar in Nautical Miles. It is assumed that the most efficient search altitude for the type of radar installation is always used, except in the case of small targets when lower altitudes are required.

Object of Search ASE ASB ASD APS-3
Schnorchel (Sea State 0 to 1) 2 2 3 6 4 9
Raft with corner reflector 2 4 5 9 10 12
Surfaced Submarine 8 8 9 12 22 22
Ship (4000 - 8000 ton) 22 20 22 30 40 40
Convoy (4 or more ships) 24 22 26 36 50 50
NOTE TO TABLE 1: The Effective Visibilities given in Table 1 are derived from average radar ranges obtainable under general maintenance and weather conditions. They are based upon representative operational results and are intended for use in making search plans on the basis of the Nomographs which follow. The Effective Visibility not only varies from one type of radar to another, but also depends upon local atmospheric conditions. In dry climates, such as the South Atlantic area, larger values may be obtained; regions of high humidity, such as the North Atlantic, may show lower values. When local data on actual average radar ranges are available, the Effective Visibility may be taken as 1.2 times the average range of contact that has been obtained by the type of radar used except for small targets with clean lines, in which case E may be less than the average operational range.

    1. The effective visibility E is roughly equivalent to the range within which there is approximately a 50% probability of contacting a given object. Thus, search of an area planned on the basis of parallel tracks separated by twice E gives an acceptable (50%) chance of making a contact with a given economical amount of flying, but does not lead to certainty in making all possible contacts. When flight tracks are placed closer together a higher probability of contact results, but considerably more flying is required to raise the probability of contact by any considerable amount.

  1. When the effective visibility has been determined, the correct search plan to be used should be selected. The choice of search plan depends upon the information available concerning the position, course, and speed of the object of search. If the forces available do not suffice to cover the probable area of search with the desired high probability of contact, it is better to search the entire area with a wider spacing between tracks than to concentrate the flying with close spacing in only part of the area.
    1. In planning parallel sweep searches (A/C Search Plan No. 1, Article 2262) for a submarine with only Schnorchel showing consideration must be given to the fact that the effective visibility for such a target depends on sea state as well as on atmospheric conditions. When flying at the altitudes prescribed in current operational instructions, E for a Schnorchel or its wake ranges from about two miles in calm seas to less than a mile in seas of force greater than 4. However, a very large proportion of all Schnorchel contacts have resulted from sighting exhaust vapors or smoke at relatively long ranges. Therefore, when atmospheric conditions favor such sightings (cool or cold weather) the effective visibility in visual


      search for Schnorchel targets is about the same as that for a surfaced submarine, when searching at the same low altitude. The effective visibility given in Table 1 for radar search applies only to calm seas, and may be reduced to less than half the values given in seas of Force 4. Sea return is greater in the upwind semi-circle; therefore as much as is practicable searches should be planned so as to minimize upwind flying. When A/C Search Plans 2 or 3A are used, the full value of Effective Visibility for surfaced submarines from either Table 1 or Table 2 will be used.

  1. With each plan is given a nomograph. This nomograph may be used to determine the probability of success of the plan for a given spacing, number of planes, and effective visibility. This probability has been computed on the basis of operational sightings data.

  1. Nomographs are mathematically computed and arranged. Great care must be taken to insure against vertical or horizontal changes in dimensions if a copy is made. Careful photographic reproduction is recommended. The table, plans, and nomographs which follow are laid out for the particular conditions listed under the titles.


    1. Table 2 - Effective Visibility for Visual Search in Nautical Miles.
Object of Search Altitude in
Meteorological Visibility in Nautical Miles
3 5 10 15 20 30 40 50
  M/V or Combatant
  Submarine or small M/V
  M/V (medium to large) or minor combatant
  Major Combatant
  Convoy or Task Force
(Use the effective visibility for a moving major combatant plus the radius of the convoy or task force.)
One-Man Life Raft Recommended
Altitude in Feet
500 650 900 950 1000 1050 1100 1150
0.25 0.35 0.45 0.45 0.45 0.50 0.50 0.55
Large Raft Recommended
Altitude in Feet
1000 1300 2000 2400 2700 2800 2900 3000
0.6 0.9 1.3 1.5 1.6 1.8 1.9 2.0


      (For systematic patrol, or for lifeboat, S/M or M/V whose position is very uncertain, course unknown, speed unknown.)
    2. TO LAYOUT PLAN 1.

      1. Determine spacing of A/C tracks a from Nomograph 1.
      2. Cover entire area to be searched with parallel sweeps.

      Plan 1


      1. Obtain Effective Visibility (Table 1 or Table 2).
      2. Lay straight-edge from Effective Visibility on Scale A through Sweep Spacing on Scale B, read Probability of Contact on Scale C.
      3. Choose spacing of A/C tracks in accordance with numbers and types of A/C available and probability of contact desired.


Nomograph 1 - Parallel Sweeps


    1. A/C SEARCH PLAN No. 2 - EXPANDING SQUARE. (Object's Position reported, course unknown, speed very small.)
    2. TO LAY OUT PLAN 2.
      1. Obtain Effective Visibility (Table 1 or Table 2).
      2. Make Search Interval (a) twice the Effective Visibility.
      3. Center Plan at reported position.
      4. Obtain Search Radius (r) (Nomograph 2).
      5. Lay out successive legs on the plan out to approximately the Search Radius minus the Effective Visibility.

      Plan 2


      1. Compute expected Center Position Error by adding in miles the estimated Error of Position Report and the A/C Navigation Error in reaching position (5% of distance from base for dead reckoning.
      2. Lay straight-edge from Center Position Error on Scale A through the Number of Search on Scale B, read Search Radius on Scale C. (Number of Search is 1 for first search, 2 for second search, etc. Search Radius is distance from center to middle of last leg plus the Effective Visibility).
      3. Read Probability of Contact at the end of any search opposite Number of Search on Scale B.
      4. Lay straight-edge from Search Radius on Scale C through Search Interval on Scale D, read Scale E. Compute Total Distance Flown, (from center back to center) by subtracting Search Radius from Scale E Reading.
      1. Keep center of search well marked with slicks or other markers.
      2. If no contact is made on Search No. 1 by the time the Search Radius is reached, return to center and start another search.


Nomograph 2 - Expanding Square


      (Object's position known, course unknown, speed estimated).
      Use for submarine hunt when the hunt is started within one hour of the time of sighting.

      Use Nomograph 3 to determine probability of contact. Use radar continuously during gambit patrol.

      1. If the submarine is not attacked, make one gambit (30 minutes).
      2. After the gambit or the attack and examination period, fly a trapping gambit square about the point of submergence as a center. The speed of the aircraft will govern the size of the square and the length of time it is held. The square should be started anew with each positive contact. Following are the lengths of legs of the square and the maximum times (following submergence) for various "speed types" of planes:
        PBY 20 miles 4 hours
        PBM, TBM 25 miles 4 hours
        PV, PB4Y 30 miles 6 hours

      4. All planes, except the PBY and slower should fly a diagonal, remarking the center at the end of about every two circuits.
      5. Not later than the end of the maximum times given above, the lengths of the search legs should be lengthened to 45 miles unless contact has been renewed. A second plane should join the search by the time the expansion occurs and should fly on the opposite side of the square and in the same direction as the original plane. Flying the diagonals should be coordinated by voice radio.
      6. At the end of 8 hours following the start of the patrol, the length of the legs should be expanded to 65 miles. At the end of 9 hours, they should be expanded to 75 miles, and a third plane added to the square. Not later than 12 hours following the start of the patrol, an additional plane should be added on a 25 mile square in the center of the area.
      7. If contact has not been renewed within about 18 hours of the start of the patrol, if there has been little of no evidence to indicate that the submarine is still within the square, or if coverage has not been completed, it probably will be advisable to discontinue the square plan and sweep through areas to which it is estimated the submarine has traveled.
      8. All relief activities should take place on the side of the square farthest from the base. Planes proceeding to or from station should cross the center of the square, marking it enroute if a previously placed marker is seen.
      9. When two planes are flying on the same square, an alternate method to that of paragraph (c) above, is to have each of the two planes fly only one-half the square, reversing course at the end of each half.
      10. It must be remembered that the aim of gambit tactics is to induce the submarine to return to the surface and provide an opportunity for renewal of contact and further attack. An excessive number of planes in the area will provide the submarine additional opportunities for sightings and may, thereby, defeat the purpose of the gambit square.


      If it is estimated that the submarine sought is attempting escape by using SCHNORCHEL (sea state 3 and below) the plan above for a hunt for a surfaced submarine is satisfactory with the exception of paragraph (e). For SCHNORCHEL search substitute the following procedure for paragraph (e):

      At the end of 8 hours following the start of the patrol, the length of the legs should be expanded to 80 miles and this square maintained at least until the next daylight period. Not later than 12 hours following the start of the patrol, an additional plane should be added on a 25 mile square in the center of the area.


      (Object's position reported, course unknown, speed estimated.)

      Use for submarine or surface craft hunt when the hunt is started after an elapsed time of more than one hour from original sighting or attack. If elapsed time exceeds four hours, additional search of the interior of the square is necessary.

      Use radar continuously during gambit patrol.

    2. TO LAY OUT PLAN 3.

      1. Compute S, the Center Position Error by adding the estimated Error of Position Report and the A/C Navigation Error in reaching position (latter error is 5% of distance from base for A/C).
      2. Compute D, the Distance Object has moved from reported position by multiplying Estimated Surface Speed of Object by Time Delay (time in hours from time of contact to estimated start of Plan). For S/M use 10 knots as speed for first two hours, 7 knots thereafter.
      3. Make L = 4S + 2D and center plan on reported position (see diagram). Displace leg nearest shore outward, if very close to shore, or over shallow water.
      4. For S/M, increase L by 20 nautical miles every 3 hours, or after every circuit if longer than 3 hours until contact is renewed. If contact is not renewed in 12 hours discontinue square plan and sweep through areas to which it is estimated the submarine has traveled.
      5. For surface craft, if contact is not renewed in one circuit, abandon search or start new plan with L greater by 4S than the L of the first search.

      Plan 3A

      TO USE NOMOGRAPH #3. (See Next Page).

      1. Obtain Effective Visibility (Table 1 or Table 2).
      2. Compute Velocity Ratio by dividing A/C speed by Estimated Speed of Object (for S/M use 10 knots).
      3. Lay straight-edge from Effective Visibility on Scale A through Velocity Ration on Scale B by turning Line C.
      4. From determined point on line C lay straight-edge through L on Scale D to Turning Line E.
      5. From determined point on Line E lay a straight-edge through Number of A/C Used on Scale F, read probability of Contact on Scale G.
      6. If probability is unacceptably low, use additional aircraft as availability permits.



Nomograph 3 - Trapping Square


  1. A/S Barrier Patrols by Aircraft
    1. An A/S barrier patrol is defined as a series of flights the purpose of which is to deny passage of a surfaced submarine through a channel or a particular ocean area. In anti-submarine patrols the probability of contact is decreased because of the normal possibility of the U-Boat traveling submerged. In mid-ocean areas and in areas where aircraft do not constantly patrol, it generally may be assumed that submarines will proceed surfaced either during the entire 24 hours or during some portion of the 24 hours (such as the hours of darkness). It is essential, therefore, that the barrier patrol be planned so that flights are made during the period that the submarine is expected to run surfaced. The effectiveness of a barrier patrol depends on its being maintained long enough to encompass the entire possible range of times of attempted transit by the enemy unit sought. For barrier patrols by carrier based aircraft refer to Article 2274.
    2. The conditions affecting the design of barrier patrols include submarine speed, aircraft speed, channel width, aircraft endurance, forces available, visibility, and the acceptable probability of contact.
    3. The principal of the basic barrier patrol design is illustrated in Figure 1. The two vertical lines represent the boundaries of the channel to be closed. The base of operations is at O. The submarine is moving down the channel at the speed u. The flight is designed to sweep over all possible enemy positions as he moves down the channel. The aircraft takes off from 0 to search for the enemy somewhere along 00'.

      Formula 1

      Because of the motion of the submarine, the actual track of the aircraft will be OA. The course of the plane is determined by the fact that the component of the speed of the plane along the channel must be equal to u. We therefore construct the right triangle OXY with XY=u and OY=v, the speed of the plane. The angle between OX and OY is then the proper lead angle. When the plane has reached the point A it turns up the channel and then sweeps back to cover the adjacent area above. Because of the motion of the enemy the length M of the up-sweep (AB in Figure 1) is given by

      Formula 1 Formula (1)

      where S is equal to the Sweeping Spacing. This Sweep Spacing is obtained by entering Nomograph 1 (Article 2262) with the effective visibility E (Article 2231, 2261) and the desired probability of contact.
    4. To close a narrow channel, the time interval between departures of successive flights will be greater than the time required to complete one flight. To close a wide channel, the time interval will be less than the time required to complete one flight. In either case, the time interval, T, between successive flights is given by the formula

    5. Formula 2 Formula (2)

    6. The maximum desired probability of contact should be used in planning a barrier patrol. If the plane requirements are found to be excessive, they may be reduced by increasing the


      sweep spacing and the interval between successive flights until the proper operating balance is obtained.

    1. A channel may be closed without continuous flying (as when it is desired to fly entirely by day, or entirely by night) by effectively searching the entire length of channel down which the S/M can travel in the interval between successive flights. The method requires the use of two or more aircraft on parallel tracks. It has the advantage that a submarine is less likely to evade it by passing submerged through its entire area.

      Figure 2

      If the submarine is believed to be surfaced only during a portion of the 24 hours, the flights should be made during this period and cover a full 24 hour run of the submarine; alternatively, these multiplane flights may be made at intervals of X hours, covering only X/24th of the submarine's 24 hour travel. The basic plan is the same as that in Figure 1. The outward legs of each track (Figure 2) are drawn as in Figure 1, and the tracks are spaced by a distance equal to S (Article 2273). The upward sweep for each track is given by

      Formula 3

      where n=additional number of planes above one, and the planes depart from B1 and B2 at the same lead angles as at 01 and 02. This plan is also of value in barring a channel so wide that when flown by one plane at a time the return leg brings the plane back to a point A1 which is too far from the starting point O.

    2. For a channel so narrow that it may be swept continuously and repeatedly by a single plane a symmetrical barrier patrol with its crossover point exactly in the center of the channel is most convenient. The Sweep Spacing S does not enter directly into the construction of this

      Figure 3

      patrol. The cross legs OA and O'A' are standard cross-sweeps with the standard lead angle. The length M of the up-sweep is chosen to place O' directly across the channel from O and A' directly


      Opposite A. The resulting Sweep Spacing may then be found by using Formula 1 and probability of contact may be found from Nomograph 1. If the probability turns out to be unacceptably low, the multiplane plan described in Article 2276 may be used to increase it.


2300 ATTACK.

  1. Normally the approach should be made by the shortest path at maximum speed. If circumstances permit, however, an attack approach through the clouds will give the best chance of achieving surprise.

  1. Strafing with machine guns shall be directed primarily against personnel. The next important target is the main engine air induction piping which extends from the lower after end of the conning tower aft for about 25 feet, then if visible, the blister or saddle tanks abreast of the conning tower. Survivors in the water shall not intentionally be fired upon.

  1. The following is a general outline of the tactics to be employed in dealing with submarines that fight back:
    1. Attacks shall be pressed home immediately upon sighting on the assumption that complete surprise has been achieved. During daylight all guns which can be brought to bear shall open fire as soon as the submarine is within range. At night, even though fired upon, withhold gunfire unless certain own plane is seen. An attack from ahead normally provides least hazard from AA fire although other conditions may dictate other approach angles. Until the range has been closed to about 1000 yards a moderate amount of weaving in altitude and direction along course will complicate the submarine's AA problem. Inside about 1000 yards the plane should be flown straight to provide a steady platform at point of release.
    2. If an aircraft has been ordered to delay attack to await support, it should circle or make figure 8's, making all turns towards the submarine. The pilot must be vigilant to detect any indication of the submarine's intention to submerge. This indication will not be readily apparent from a position in line with the submarine. If such indication appears, he shall attack immediately. This will require his remaining within close range while awaiting support. A support aircraft approaching shall notify the original aircraft by voice radio as soon as sight contact is made, giving his approach course and estimated time of arrival. The original aircraft shall then take station on the far side of the target and attempt to hold the enemy's attention by gunfire or other means. The approaching aircraft shall make every effort to get in his first attack undetected.
    3. Two or more aircraft in company shall deliver a coordinated attack. The general details of coordination should be planned in advance and shall be well practiced. These plans shall be simple, flexible and capable of rapid execution. In general, the identity of the O.T.C. shall be a matter of prescribed doctrine; the attack signals shall be specific; and the sequence of action shall be laid down. It must be remembered that the interval between the time the depth bombs hit the water and the time their plumes reach full height is about 15 seconds. An appropriate interval between successive depth bombing attacks must, therefore, be provided.

  1. Depth Bomb attacks shall be conducted with proper consideration being given to the following factors:
    1. An attack nearly along the fore and aft line of the submarine insures the greatest probability of success, but this angle shall never be chosen at the expense of a direct approach. Depth bombs shall be released in train using the prescribed spacing. Bombs shall be dropped from an altitude in the neighborhood of 100 feet, or lower if practicable, except in the case of glide attacks where release should be made from the lowest altitude that will permit a safe recovery.
    2. The point of aim in a depth bomb attack shall be such that the center of the stick will explode at the conning tower of the submarine. If the submarine is on the surface, use the bow as the point of aim. The following factors combine to determine the points of aim for a submerged submarine:
      1. Length of time that submarine has been submerged when bombs are released.
      2. The forward speed of submarine.
      3. Total time of travel of the depth bombs from release to explosion.
      4. The forward underwater travel of the bombs from impact to explosion.


    1. The following diagram presents the factors involved in solving position of impact:
    2. Position of Impact

    3. The graphs below illustrate the difference in diving times and turning circles for the most frequently encountered types of German and Japanese submarines: i.e., the 500-ton German U-Boat and the large Japanese I class cruiser submarine (about 2190 tons). Figure 1 shows the depth of the center of the hull for maximum diving speed without turning. Forward advance for both Japanese and German submarines is 10 ft./sec. but the German descends at a greater rate. Figure 2 shows the distance of the center of the hull from the diving track during a turn after submergence.
    4. Charts


    1. The following graph presents the lethal range of Torpex and TNT against the pressure hull of a submarine.
    2. Lethal Range Chart

    3. The following depth bombs, with fuzes which can be fitted, shall be used by anti-submarine aircraft:
(German) (Japanese)
AN-MK 17
Mod. 2
243 lbs. T.N.T. 344 lbs. Nose AN-MK 219
Side AN-MK 234
60 ft. 70 ft.
AN-MK 41 227 lbs. T.N.T. 330 lbs. Nose AN-M 103A-1
Side AN-MK 234
60 ft. 70 ft.
AN-MK 47 252 lbs. TORPEX 354 lbs. Nose AN-M 103A-1
Side AN-MK 234
70 ft. 80 ft.
MARK 54 250 lbs. TORPEX 354 lbs. Nose AN-MK 219
Tail AN-MK 230
70 ft. 80 ft.
NOTES: (a) Hydrostatic fuzes for aircraft depth bombs shall be set for 25 ft.
(b) At night - impact spacing for all depth bombs shall be 80 ft.
(c) Underwater travel of all 350 lbs. flat nose D/B's is 35 ft. within normal speed entry limits.


    1. The impact spacing of bombs released from an aircraft in a glide is dependent upon the angle of glide and altitude and air speed at release. The graph below gives the intervalometer setting for the release air speed desired to obtain an impact spacing of 70 feet. If a 60 or an 80 foot spacing is desired, the value found from the graph will be multiplied by either 60/70 or 80/70 respectively.
    2. Impact spacing

    3. Aircraft carrying depth bombs only shall carry at least four, if practicable, and as many more as the characteristics of the aircraft and the mission permit. In addition, sea markers shall be attached to bombs to mark the positions of bomb impacts.
    4. The number of bombs to drop on an attack shall be determined in accordance with the number carried, the conditions at the time of the attack and the mission of the aircraft. Normally aircraft carrying more than six shall drop all bombs on the first attack. Those carrying more than six shall drop six on the first attack, and any over six shall be kept for subsequent use. The following considerations, however, shall govern:
      1. A Class A attack is defined as an attack that is made on a surfaced submarine or one that has been submerged not longer than 15 seconds (German) or 20 seconds (Japanese).


      1. A Class B attack is defined as an attack that is made on a submarine that has been submerged from 15 to 30 seconds (German) or 20 to 40 seconds (Japanese).
      2. The decision as to whether hydrostatically fuzed depth bombs should be dropped on a Class B target rests with the commander of the attacking aircraft. If the submarine has been submerged for 30 seconds (German) or 40 seconds (Japanese) or more, when the release point is reached, no bombs shall be dropped. These bombs should be saved for use in gambit.



  1. A contact report by radio shall be made as early as possible after a sighting followed by necessary amplifying reports. If friendly forces are in the vicinity, energize IFF on the designated contact channel immediately after making contact unless otherwise directed.

  1. After a radar contact is made and an approach started the rate of approach shall be accurately calculated. This is to assure that, if the target is lost before visual contact is made, a dead reckoning run may be made to the position of the contact for marking and commencement of re-contact operations.

  1. After sighting or attacking a submarine which then submerges, the aircraft shall mark the spot of submergence. If equipment for direct underwater tracking is not available it should then employ gambit tactics in an effort to induce the submarine to return to the surface. If an attack has been delivered the aircraft should examine the area for evidence of damage for about 15 minutes before commencing a gambit patrol.
    1. The trapping square and continuous gambit have proven to be the most efficient and most economical type gambit. This type plan is presented as Aircraft Search Plans Nos. 3 and 3A, Article 2264 and 2265.

    [Editors Note: The source material did not include an entry for Article 2432, nor did the index. - HyperWar Editor]

    1. In calculating possible submarine positions, assume surface speeds of 18 knots for the first hour and 12 knots thereafter, submerged speed of 6 knots for the first 10 minutes and 3 knots thereafter.

  1. When submarines are damaged sufficiently to prevent their submerging and their crews realize that capture is imminent, they may attempt to scuttle ship. To prevent this, direct bursts of machine gun fire at the crew. The aircraft alone is not in position to accept surrender of a submarine.

  1. In the event a neutral ship or ship of unknown character approaches an enemy submarine or its personnel before the submarine is believed or known to have been sunk, that ship shall be warned away by firing across its bows. If within a reasonable time this warning is not headed, the disobeying ship shall be attacked. A neutral ship shall not be prevented from rescuing survivors once the submarine has been sunk.



  1. Illumination shall be used whenever its use will be of assistance in conducting an attack. Possibility of illuminating friendly ships will be accepted if such illumination will enable aircraft to drive home the attack.

  1. Coordination of the highest degree between crew members is an absolute necessity in the execution of a night attack in order to achieve surprise, identify the target, carry out the attack, and recover safely.


  1. Combined use of searchlight illumination and radar provides the most successful technique for night attack on enemy submarines. Only the most proficient instrument pilots should be employed in this type of operation. The loss of dark adaptation induced by illumination and the task of going from instrument flight to contact and back to instrument requires exceptional skill in retaining control of the aircraft.
    1. Search altitudes should not exceed 1500 feet. This should provide the fullest advantage of detection equipment and enable the aircraft to attain the approach altitude readily.
    2. Upon radar contact the aircraft should descend to 200 feet as rapidly as possible maintaining contact and homing by radar.
    3. The searchlight should be turned on at such a distance from the target as to provide for such alterations in course as necessary for making an accurate attack. This distance will vary from one-half to one mile depending upon the rate of approach and the proficiency of the pilot and crew.
    4. Immediately upon illumination of the target, the pilot goes on to contact flight and carries out the attack by visual as in daylight. The instant the bombs are released the searchlight should be turned off and an instrument recovery effected.

  1. Aircraft parachute flares can be used as an effective means of illumination for night attacks if reasonable consideration is given to the characteristics of the equipment and to the employment procedures.
    1. A vertically falling flare must be released from the aircraft within approximately 1/2 mile of the target in order to provide sufficient illumination for identification and attack. This necessitates maneuvering in the proximity of the target thereby sacrificing some degree of the element of surprise.
    2. Delayed ignition of the flare after dropping is of extreme importance in order to achieve surprise and to permit the aircraft to maneuver from the flare release position into position for attack. The ignition delay should be no longer than required by the capabilities of the aircraft. The following ignition delays are recommended for type aircraft as indicated:
    3.   TYPE
      (a) Mk 8 90 sec. PV
      (b) Mk 8 120 sec. PBY
      (c) Mk 5 or 6 300 feet All 1500

    4. Altitude for search, when flares are to be employed, should be 1500 feet for the Mk 5 or 6 and 2000 feet for the Mk 8. If weather conditions limit the search altitude to less than the designated altitude, the decision as to the feasibility of climbing to flare release altitude during approach rests with the pilot.
    5. Upon obtaining radar contact, the aircraft should turn as quickly as possible towards the target and commence homing by radar, making an accurate check on the relative movement (component due to target movement and wind drift). A course should be set to pass through a point 1/4 mile from the target in the direction of the relative motion. Specific procedures are outlined in the diagrams following.


    1. Diagram of Attack Under Normal Conditions with 90 Second Delayed Ignition:
      1. Head directly towards target, set gyro to zero and hold course to determine relative movement by radar.

      3. Change course to intercept at 1/4 mile in direction of relative movement. Start stop watch.

      5. Check time on stop watch and commence timing approach. (Radar "blip" might disappear in "sea return" on close approach.)

      7. Drop first flare at 1/2 mile (radar) or at twice the time from (b) to (c) (stop watch) and turn 45° away from target.

      9. Release one or more flares at short intervals and commence rapid let-down. (1000-1500 ft. per minute.)

      11. At (d) time plus sixty seconds commence 225° turn to the reciprocal of the approach heading.

      13. Continue turn to the reciprocal of the approach heading, searching in the flare paths for target. Upon sighting, carry out visual attack.


    1. Diagram of Attack Under Normal Conditions with 120 Second Delayed Ignition:
      1. Head directly towards target, set gyro to zero and hold course to determine relative movement by radar.

      3. Change course to intercept at 1/4 mile in direction of relative movement. Start stop watch.

      5. Check time on stop watch and commence timing approach. (Radar "blip" might disappear in "sea return" on close approach.)

      7. Drop first flare at 1/2 mile (radar) or at twice the time from (b) to (c) (stop watch) and turn 40° away from target.

      9. Release one or more flares at short intervals and commence rapid let-down (1000-1500 ft. per minute.)

      11. Commence two-needle width turn at (d) time plus 60 seconds continue until on the reciprocal heading.

      13. At plus 120 seconds aircraft should be at 300 ft. altitude. Search in flare path for target. Upon sighting conduct visual attack.


    1. Diagram of Attack Under Normal Conditions with 300 Foot Delayed Ignition (Mk 5 or Mk 6 Flare):
      1. Head directly towards target, set gyro to zero and hold course to determine relative movement by radar.

      3. Change course to intercept at 1/4 mile in direction of relative movement. Start stop watch.

      5. Check time on stop watch and commence timing approach. (Radar "blip" might disappear in "sea return" on close approach.)

      7. Drop first flare at 1/2 mile (radar) or at twice the time from (b) to (c) (stop watch) turn away from target and commence rapid let-down (1000-1500 ft. per minute). Drop at least one extra flare in succession after first.

      9. Make turn to attack sub visually dependent upon speed of A/C and relative motion of target. Flares will burn approximately 2 minutes.



  1. The necessary deviations from standard instructions for aircraft and special instructions applicable only to airships are contained in this section.

  1. Attacks against submarines shall be conducted in accordance with the following instructions:
    1. The possibility that an airship can deliver a successful daylight bombing attack on a surfaced submarine that fights back is low. Under these conditions the airship shall summon support and maintain contact with the submarine. The airship should approach to just outside the effective gun range of the submarine and by feints attempt to keep the submarine's attention engaged and the submarine surfaced. The submarine shall be closely observed and on first indications of submergence the attack shall be launched.
    2. Due to present lack of suitable illumination equipment for a night attack the airship must usually approach within a few hundred yards to identify the surface object. Normally the airship will be in such a position that it is better to attack than to attempt to withdraw if the craft proves to be an enemy. The airship, therefore, must make every approach on an unidentified surface craft with the intention to attack.
    3. After the submarine has been submerged for 30 seconds or more the attack shall be withheld and M.A.D. tracking procedure instituted, and contact maintained until support arrives or until a well developed M.A.D. attack is possible. Airships shall not normally attempt gambit tactics.
    4. In delivering an M.A.D. attack the airship should proceed along the estimated track of the submarine and when signature is received, release a marker. Course should be continued and six seconds later another marker released followed by a tight turn to the right of 330°. Head for the last marker dropped and release stick of bombs, straddling the last marker.
    5. If the initial contact is made with the submarine submerged, hydrostatically fuzed bombs shall be withheld in expectation that the submarine may show its periscope or surface, when a more profitable attack can be made.

  1. Depth settings for hydrostatic fuzes shall be as follows:
    1. For day missions all hydrostatic fuzes shall be set for 50 feet.
    2. For night missions the fuzes shall be set to the standard 25 foot depth.



  1. The Expendable Radio Sono-Buoy is an instrument designed to receive underwater sonic noises and transmit them for radio reception.
    1. The principal uses of sono-buoys are:
      1. Localizing the position of a submerged submarine to a relatively small area for future attack by surface ships or by aircraft.
      2. Gambit Tactics.
      3. Determination of damage or of the effectiveness of attack.
      4. Investigation of disappearing radar contacts.
      5. Investigation or evaluation of M.A.D. indications.
      6. Investigation of oil slicks.
      7. Location of survivors.
      8. Ship-to-plane and plane-to-plane communication.


    1. Success in the use of sono-buoys depends on the ability of a plane to remain oriented with respect to the buoys by the use of sea markers and by keeping an accurate geographical position plot.
    2. The pilot should not spend valuable time listening to doubtful indications prior to completion of the sono-buoy pattern. If the circumstances justify the use of more than one sono-buoy, the full pattern should be laid expeditiously for the purpose of gaining the advantage of comparative listening.
    3. Pilots must be thoroughly indoctrinated in the types of patterns used and methods of expeditious placement. Crew members must be thoroughly indoctrinated by means of sono-buoy training records so that they will be able to recognize and describe sounds they have heard.
    4. Gambit with sono-buoys is profitable when no assisting surface craft are expected and the aircraft is capable of delivering an attack (or another aircraft, so capable, is expected to arrive). The buoy may detect the shift from electric motors to Diesels, owing to the distinct differences both in quality of the sound and the increased RPM on the surface, thus making it possible to tell the moment of surfacing. In many cases, however, the first indication picked up by the buoys will be the submarine underway at high speed after surfacing. Suitable dye sea markers other than drift signals should be used when gambit is employed.
    5. The gambit operation consists of laying a pattern of sono-buoys as indicated in article 2718. The aircraft then retires to the normal square Search Gambit, flying away a distance equal to twice the aircraft's visual range on a submarine, then flying a square each side of which is equal to four times the visual range.

    6. Procedure for Laying a Sono-Buoy Pattern on an Enemy Submarine Which Has Submerged After Visual Contact.

      • Proceed to point of submergence with directional gyro set on 000°. 1500 yards prior to reaching the point, drop 1st Sono-Buoy.
      • Continue on course and drop 2nd Sono-Buoy at the point of submergence.
      • Continue on course for 1500 yards and drop 3rd Sono-Buoy.
      • Commence 270° turn to the left. Hold turn and straighten out on heading 090°. Drop 4th Sono-Buoy at estimated 1500 yards short of 2nd Sono-Buoy.
      • Continue on 090° and note time of passing over 2nd Sono-Buoy. Drop 5th Sono-Buoy 1500 yards from 2nd Sono-Buoy on course 090°.


    1. Diagram of Sono-Buoy Pattern to Be Used After Disappearing Radar Contact and in Conjunction with Aircraft Square Search Gambit.

      After laying a pattern of Sono-Buoys around the Submarine as indicated in the diagram, the A/C then retires to the normal Square Search Gambit flying away a distance equal to twice the A/C's visual range on a submarine, then flying a square each side of which is equal to four times the visual range.

    3. Procedure for Laying a Sono-Buoy Pattern on a Suspicious Surface Indication Such as Oil Slicks and Oil or Air Bubbles.

      Proceed to Position of suspicious indication with directional gyro set at 000°, release first Sono-Buoy, and commence 180° turn to the left listening for submarine.

      Continue turn to 180° (Gyro) and drop second Sono-Buoy, if submarine is heard on number one buoy. At release of second buoy, reduce rate of turn, laying third Sono-Buoy at 90° (Gyro), fourth Sono-Buoy at 000° (Gyro), and fifth Sono-Buoy at 270° (Gyro). The rate of turn must be varied to compensate for wind drift.

      Note - If no submarine is heard on first buoy, discontinue pattern and resume mission.

  1. The following general instructions will be observed by aircraft equipped with the Sono-Buoy Magnetic Wire Recorder.
    1. The recorder will not be run continuously. Intermittent operation for recording of important sounds with short commentary on time and color of buoy transmitting is sufficient.
    2. Sono-Buoy transmissions just prior to an attack and 15 minutes thereafter shall be recorded.

  1. A large Sono-Buoy Pattern may be laid for the purpose of localizing a submarine known to be in a limited area.
    1. The following conditions must exist in order to expect acceptable results from a large Sono Buoy pattern:
      1. The submarine is known to exist in a limited area, the size of which depends upon the reliability of the estimate of the submarine's position.
      2. The sea state is low (0 to 1).
      3. The submarine will be moving for at least a part of the time at a speed of at least two knots within the limits of the pattern during the lifetime of the Sono-Buoys.

    2. The following procedure will be observed in laying and monitoring the pattern:
      1. The size of the Sono-Buoy pattern will be large enough to insure certainty that the U-Boat is contained within the pattern.
      2. The pattern will be laid in the form of a square or a rectangle of equally space buoys, the number of which, for a particular probability of contact, may be determined by Table A below.
      3. Unless the area is very small, no one plane will lay or attempt to monitor more than six buoys.


        When an indication is picked up on a particular frequency (green, for example), each plane will immediately fly at low altitude (200-300 feet) over the buoy of that particular frequency (green, for example) to ascertain whether the buoy is giving the signal. When the buoy is identified, the aircraft will then develop the contact in accordance with doctrine.  

        Table A
        For a Submarine Unit Area of 100 Sq. Miles
        No. of
        Sono Buoys
        Probability of Contact
        (Sub Speed 2 kts. Periscope Depth)
        12 .16
        18 .24
        24 .32
        36 .40
        42 .47
        48 .52

    The probability of contact is given for a unit area (area in which submarine is known to exist) or 100 square miles. If the area is A square miles the number of buoys for a particular probability of contact should be multiplied by A/100. For example, if A equals 200 square miles, multiply the number of buoys by two. Then 24 Sono Buoys will give a probability of .16, 36 buoys will give a probability of .24, etc.

  1. After Sono Buoy Contact has been obtained tracking may be continued outside of the limits of the original pattern in accordance with the following examples:

    1. Case No. 1 Example:
      Good submarine indication first heard on buoy No. 2, then quite definitely on buoy No. 1, but not particularly well on either buoys No. 4 or No. 5.
    2. Case No. 2 Example:
      Good submarine indication heard on buoy No. 2, then quite definitely and equally well on buoys No. 1 and No. 4.
    3. Case No. 3 Example:
      Good submarine indication heard on buoy No. 2, then quite definitely on buoys No. 1 and No. 4, but much louder on No. 4 than No. 1.


    1. In connection with the tracking procedure care should be exercised in monitoring frequencies for which more than one buoy is laid. Two buoys of the same color should be laid as far apart as possible. If a submarine indication is received on a frequency for which more than one buoy is down the procedure in 2732(d) should be followed.
    2. When a silent buoy starts transmitting of when a transmission is intensified an interpretation of the sounds may establish (a) that the submarine is approaching the buoy or (b) that it has speeded up. In the latter case if A/S vessels are within the U-Boat's listening range (about 15 miles for a 15 knot DD is a sea state of 0-1) such Sono Buoy indication may be taken to indicate that the submarine has determined upon offensive of evasive action. In interpreting these indications it should be borne in mind that generally a slow moving U-Boat will hear surface craft somewhat before they are picked up over Sono Buoys.

  1. The graph shown below is designed to give information regarding Sono Buoy ranges on enemy submarines. Average sound conditions are assumed. Actually the ranges may vary from one-fourth to four times the ranges shown and in about one-half the cases the ranges vary from 70% to 140% of the ranges shown. Maximum distance at which DE's without FXR may be heard over Sono Buoy under average conditions are also given for comparison.



  1. Aircraft rocket projectiles are effective against a submarine in any state in which the hull or conning tower is visible.
    1. Rocket fire from both bombing and fighting planes shall be aimed to sink the submarine.
    2. Rocket fire from bombing planes shall not be delivered to the detriment of an accurate attack with depth bombs.
    3. Machine gun strafing against the submarine's anti-aircraft guns should be started at about 2000 yards range during the approach but shall not be continued to the detriment of an accurate rocket attack.

  1. The target angle for most effective penetration is from directly on the beam. Any approach in excess of 45° forward or abaft the beam is ineffective.

  1. A glide angle between 10 and 20 degrees should be used in order to get satisfactory horizontal underwater trajectory.

  1. The point of impact for the rockets should be a point 20 feet short of the waterline under the conning tower.



  1. The Magnetic Airborne Detector is an instrument designed to detect disturbances in the earth's magnetic field.

  1. In anti-submarine operations M.A.D. is used to verify the presence of, and to determine the position of submerged submarines.
    1. Barrier patrols may be set up in restricted areas to detect the presence of submarines attempting to traverse the area.
    2. Investigation of oil slicks and other suspicious surface indications is made by conducting parallel sweeps or an expanding square search of the area. It should be remembered that the effective M.A.D. detective range is short. No attempt should be made to search large areas.
    3. The position of a submarine is determined by trapping and tracking procedures.
      1. Trapping is defined as the tactics employed to establish initial M.A.D. contact.
      2. Tracking is defined as the tactics necessary to maintain contact and determine the movements of the submarine after initial contact.
      3. These tactics will be employed when the possibility of joint air-surface action exists.

  1. HTA Aircraft Employ the Following Tactics:
    1. When a submarine is seen to submerge, or when a bona-fide radar contact disappears, the spot shall be marked and an initial sweep made over the estimated point of submergence.
    2. If contact is not made, a trapping circle shall be established around this point as indicated below. This shall be a "3 minute circle," i.e., a circle that requires 3 minutes to traverse its circumference. The length of time to continue circling depends on the speed of the airplane: forty-seven minutes for 110 knots, to sixty-five minutes for 150 knots.


    1. When contact is established by means of the trapping circle, tracking procedure is commenced as indicated below.
    2. Tracking is accomplished by employing the following clover leaf pattern until course and speed of the target can be determined as required for attack with suitable weapons, or until surface craft arrive on the scene.


  1. LTA Aircraft Employ the Following Tactics:
    1. When a submarine is seen to submerge or when a bona-fide radar contact disappears, the approach to the point of submergence and trapping tactics shall be performed at maximum practicable speed.
    2. Trapping procedure shall be instituted in accordance with the below diagram when the elapsed time after submergence of submarine is up but not more than four minutes.
    3. When the submarine has been submerged longer than four minutes but less than fifteen minutes, the trapping circle shall not be commenced until the airship has proceeded for one mile past the point of submergence. The radius of the trapping circle then becomes one mile.
    4. When an airship arrives more than fifteen minutes after submergence, hold-down tactics shall be employed.
    5. When the initial contact is made, tracking procedure shall immediately be initiated:
      1. The tracking pattern consists of 270° turns always to the right in a clover leaf pattern. The turns shall be as tight as practicable and continued until the movements of the submarine are determined. Each contact should be marked.
      2. If at the end of any turn, contact is not made within a reasonable time of the estimated point, a new turn shall be started. If at the end of two successive turns no contact has been made, a trapping circle of 1000 foot radius shall be made about the last point of definite contact and maintained for five turns, after which the standard trapping circle is employed if contact is not regained.


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