Chapter IV

Section 1
Attacks -- General

4101. Employment of the principle of surprise is the basic requisite of a successful submarine attack. This essential must be obtained by painstaking attention to every detail of operation that will enable the submarine to avoid being discovered by being sighted, heard, or otherwise located.

4102. The basic attack unit is the individual submarine. Close or rigid formations are not ordinarily suitable for submarine attacks because each submarine must normally maneuver independently to attack.

4103. The objectives of submarine attack are enemy ships and shipping. If a choice is offered, priority is as follows: CV, BB, ACV, AO, any man of war larger than a DD, AP, AK, DD. However, no worthwhile target should be passed up in the hope of securing a better one.

4104. Submarines will attack individual ships of a formation. Only under exceptional circumstances or during a night attack will torpedoes be fired at a formation without using an individual ship target.

4105. Every decision concerning the approach and attack should be based on the assumption that the enemy suspects the presence of submarines and has taken the following defensive measures:

      1. Is zigzagging at moderate to high speeds.

      2. Has protective screens of aircraft and surface vessels, the latter equipped with listening or echo-ranging apparatus, or both, and

      3. Will maneuver to avoid submarines or torpedoes sighted.

4106. In conducting the approach and attack, use must be made of all facilities furnished. Readiness for every eventuality must be maintained. Even when conducting the approach by periscope, the sound equipment must be in use in order that, if forced to deep submergence, the attack can be completed by sound alone.

4107. Definitions:

      1. Approach -- The maneuvers of a submarine to reach a favorable attack position.

      2. Attack -- The maneuvers of a submarine after approach to reach a firing position. Attack is concluded by torpedo fire.

      3. Retirement -- The maneuvers of a submarine after concluding attack to avoid counter-attack and clear other attack units.

      4. Approach course -- The course taken from contact to reach the attack position.

      5. Normal approach course -- The course which, at right angles to the bearing of target, closes the range.

      6. Attack course -- The course from the attack position to reach the firing position.

      7. Firing course(s) -- Heading(s) on which torpedo fire occurs.

      8. Angle on the bow -- Relative bearing of submarine from the target ship measured to starboard or port from the target ship's head from 0° to 180°.

      9. Track angle -- The angle at the point of intercept between the target ship's track and the reversed direction of the torpedo track. It is measured to starboard or to port from the target's ship's head from 0° to 180°.

      10. Sight Angle -- The angle between the bearing of the target at the instant of firing and the torpedo track. Sight angle is not used as such in submarine torpedo control, but it should be understood for a full understanding of other terms.

11. Correction for parallax -- An angular correction applied to calculated sight angle in angled shots to compensate for the error due to the separation of the torpedo tube from the periscope. In firing on sound bearings, parallax is the angular correction applied to compensate for the error due to the separation of the torpedo tube from the sound receiving instruments combined algebraically with the angular correction applied to compensate for the error due to the distance between the center of the target ship and the propellers thereof, and the angular correction caused by the movement of the target while the propeller sound is traveling to the sound receivers.

12. Correction for advance and transfer -- An angular correction applied to a calculated sight angle in angled shots to compensate for the advance and transfer of the torpedo in turning to its final track.

13. Gyro angle -- An angle applied in the mechanism of a torpedo gyro before firing which causes the torpedo, immediately upon launching, to turn through an angle and steady on a course differing from the direction of the torpedo tube axis at the moment of firing. Gyro angle is referred to the axis of the submarine, measured from 0° clockwise through 360°.

    Examples:

    	Gyro Angle
    Straight shot from bow tube		0°
    Straight shot from stern tube		180°
    90° right angle shot from bow tube		90°
    90° right angle shot from stern tube		270°
    90° left angle shot from bow tube		270°
    90° left angle shot from stern tube		90°

14. Periscope angle -- The angle between the fore and aft line of the ship and the line of sight of the periscope when the periscope is correctly set for existing conditions. It is the algebraic sum of the sight angle, the gyro angle, the correction for parallax, and the correction for advance and transfer of the torpedo. It is set on the periscope azimuth circle as an angle measured clockwise from the ship's head (0°) through 360°.

15. Salvo -- A number of torpedoes fired from a submarine at small intervals at the same target.

16. Volume of fire -- The number of torpedoes in a salvo.

17. Spread -- A spread consists of a salvo of torpedoes fired to hit at different points along the length of the target or its length extended. There are three forms of spread:

    1. Longitudinal spread. A pattern formed by firing a succession of torpedoes along a practically identical track. The submarine steers a constant course and uses the same periscope and gyro angles, but fires at different points of aim on the same target.

    2. Divergent spread. A fan-like pattern formed by a succession of torpedoes fired at the same point of aim but with gyros set to such angles that torpedoes cross the target track at different points. This is not to be confused with the change in gyro angles necessary to make all torpedoes of a salvo hit the target at the same point.

    3. Parallel spread. A pattern formed by firing torpedoes simultaneously from bow and stern tubes with gyro angles set so that the torpedoes run parallel.

18. Spread angle is the additional gyro angle, over that required for hitting the same point of a moving target, set on the torpedo to make any type of spread.

19. Advance is the perpendicular distance between torpedo final course and a line through the tube muzzle parallel and in the same direction as the torpedo final course.

20. Intercept Point is the intersection of torpedo and target tracks.

21. Large parallax exists when the advance of the torpedo is opposed to the general direction of the target's course.

22. Small parallax exists when the advance of the torpedo is in the same general direction as the course of the target.

23. Submarine speed is the speed through the water as determined by underwater log. (Those submarines which have no underwater logs determine their speed in accordance with definition in F.T.P. 183).

Section 2
Initial Contact

4201. When the first knowledge of the near presence of the enemy is obtained from a contact report, proceed to attain a position ahead of, and out of sight of, the ship or force (including any screens) reported. Proceed on surface as long as it can be done without discovery by ship or plane. If unable to reach a position ahead of the enemy, take up one in an area he is expected to pass through or one astern, where he may be attacked, if he reverses course.

4202. To avoid discovery by an aircraft screen, the submarine should dive when from thirty to forty miles ahead of a large force. (See Article 1122).

4203. When smoke, a ship, or a force is sighted, the first action of the submarine should be directed toward avoiding being sighted. Determine the direction of movement of the ship or force sighted and proceed at once to gain a position ahead for attack. Establish the hostile nature of the force contacted as soon as practicable. Do not abandon the attack until it is clearly evident that an attack position cannot be reached.

4204. Endeavor to make a contact report if other submarines are in the vicinity, but in doing so, do not jeopardize the success of the attack by operations which may lead to discovery unless the primary task is information.

Section 3
Approach

4301. During the approach, the task of the submarine is to gain undetected and without delay, a position ahead of the enemy.

4302. The above requires the use of aggressive tactics -- tactics in which, consistent with remaining undiscovered, speeds and courses are promptly taken that will most quickly and most surely place the submarine in position for a successful attack.

4303. During the conduct of the approach, the problem of avoiding discovery by enemy surface vessels and aircraft is a major consideration. It is therefore necessary that the following precautions be given the most careful attention:

      1. Avoid sound screens, if possible, or penetrate them by use of tactics outlined in Chapter V.

      2. Run deep between periscope exposures or when making high speed in order to avoid detection by aircraft.

      3. Expose periscope at slowest practicable speeds only, using minimum exposure of periscope compatible with sea conditions and reducing time and number of exposures as much as circumstances will permit.

      4. Use silent running speeds in vicinity of sound screens.

      5. Exercise extreme vigilance to guard against oil and air leaks.

Section 4
Operating Procedures to Avoid Detection

4401. The following procedures cover cardinal principles for effective periscope handling when it is necessary to avoid detection from that source:

      1. Consistent with condition of the sea and with possibilities of air patrol overhead, the periscope must be used as sparingly as practicable regardless of the range of the target. Extensive training is necessary to become proficient in making rapid and accurate observations. Frequent time studies by the individual officers concerned constitute the best means of determining this proficiency. In an attack, the situation which usually demands the longest exposure is the last observation just prior to firing and this coincides with the time that discovery is most likely and also most undesirable. However, correct firing bearings are essential to torpedo hits. It is good practice to fire all torpedoes with periscope continuously on the point of aim, correcting the T.D.C. set-up between each shot of a salvo of torpedoes. Periscope should then be housed immediately.

      2. After running at high speeds, ample time must be allowed for deceleration before exposing periscope. The periscope should be exposed only at the slowest possible speed. Backing may be used to increase deceleration; do not back longer than thirty seconds at one time as depth control may be affected or the additional wake may be sighted from the air.

      3. All periscope exposures should be as brief as possible consistent with circumstances and the obtaining of accurate data, the latter being particularly important at those points considered essential for the speed plot. Two or more brief exposures of less than 30 seconds are preferable to a long exposure. The minimum amount of periscope should be exposed and a change of depth of over one foot should be reported to the conning officer.

      4. The periscope should be trained to the approximate bearing of the target before it is exposed.

      5. Upon completion of the observation, the periscope must be lowered promptly.

      6. Quick panoramic views should be made in low power, followed by a more searching observation in high power when not engaged in the final stages of the attack, particularly when there is a possibility that all ships in the vicinity have not been located.

      7. Consistent with sea conditions and circumstances, expose only sufficient periscope to observe efficiently. This becomes increasingly important as the approach progresses. This requires good trim and close coordination between conning and diving control.

      8. With our present system and installation of periscope operating switches, periscope exposures are considerably shortened by having someone, other than the observer, operate the periscope hoist control.

      9. Observations at three minute intervals or multiples thereof have the advantage of simplifying manual plots, but lose their effectiveness when they are allowed to become restrictive to the approach officer.

      10. Periscopes should be run all the way down when in close proximity to screening vessels and when trying to avoid detection from the air.

      11. Except when being used by a lookout, periscopes are completely housed when running on the surface and so kept until reaching periscope depth after the diving signal has been sounded. It should be standard practice to house periscopes fully on surfacing as soon as safety considerations permit. It must be remembered that a periscope projecting above the horizon, can be picked up with good binoculars at surprisingly long ranges.

4402. Under current conditions of experience and development, the following procedure has been found most effective to penetrate supersonic screens and to escape when once detected:

      1. In the absence of positive information to the contrary, it should always be assumed that enemy vessels, and especially destroyers and light cruisers, are equipped with supersonic echo-ranging and listening equipment.

2. Any screen should be assumed to be augmented by air patrol. If detected by the latter, the problem of the supersonic screen becomes much simpler.

3. In penetrating supersonic screens or passing through areas covered by patrols so equipped, the submarines should be guided by the following general principles:

   1. Performance of echo-ranging equipment varies with localities and water conditions, being best in deep water with no temperature gradient, current strata, etc., and with a slightly choppy sea. Performance is least effective in smooth shallow water. Water conditions in the particular area of operations should be ascertained by the submarine and full advantage taken of any favorable conditions.

      Other things being equal always avoid a supersonic screen if practicable. The hazard of penetration must be accepted if destruction of the screened vessel warrants. This may be frequently accomplished undetected. In the case of a valuable enemy heavy ship target, an attempt to outflank the supersonic screen should not be made if it jeopardizes the opportunity to drive home the attack, and in this case, penetration of the screen must be attempted at all costs.

   2. Full use of own sound equipment must be made to intelligently avoid or penetrate supersonic screens and patrols. Effective sound range should be determined from predicted sound range tables in order to act intelligently to avoid detection by supersonic screens.

4. When arriving within contact range of the supersonic screen, maintain steady minimum speed with all unnecessary auxiliaries secured. Run with one or both propellers at the silent running speed determined by sound tests. Avoid speed changes. Present smallest possible target by heading toward or away from the screen. Cross the wakes of advanced screens to assist in penetrating inner screen. Avoid using own echo-ranging equipment unless certain that it will not be detected by equipment available to the enemy.

5. If the submarine has been detected by a hostile ship, the need for stealth is at least temporarily non-existent and evasive tactics should be adopted. Detection is usually indicated by steady bearing and high speed of the surface vessel accompanied by strong rapid supersonic signals remaining trained on the submarine.

6. If detection is positively indicated, a quick turn at high speed to a course normal to the enemy may make him miss astern. At this point, own supersonic equipment may be useful for maneuvering to avoid and for confusing enemy signals if they are on approximately the same frequency. If practicable, time the turn so that when it is detected by the enemy, it will be too late for him to follow. Once inside the enemy's turning circle, an escape may be made in the ensuing confusion. Try to keep own and enemy's wakes between the submarine and her pursuers. If known, take advantage of blind spots in his equipment.

7. Extreme depth in itself, unless there are accompanying advantageous water conditions (temperature gradients) at lower levels, is ineffective in escaping a supersonic screen.

8. As soon as the pursuit has been shaken off, proceed as before and attempt to avoid further detection.

9. Depending on the mission and other circumstances that the submarine commanding officer must evaluate, close pursuits may warrant the use of torpedoes against pursuing craft.

10. For avoiding screens and patrols fitted with sound equipment other than echo-ranging, the submarine should make full use of its own listening gear for tracking purposes. Minimum speed, together with hand operation of all possible auxiliaries, is in order under these circumstances. Lie on the bottom if practicable. If located, run at high speeds when the enemy is coming in to attack, and stop and coast when he stops to listen. In the past, deliberate oil slicks and blowing of debris out of torpedo tubes or garbage ejectors has been an effective means of shaking off pursuit.

11. If convoy or heavy ships are present, attempt to get close to them as escorting vessels probably will not drop depth charges near them.

12. A persistent enemy may remain in vicinity 24 hours or longer; therefore, conserve the battery by balancing or bottoming, when practicable.

4403. When exposed to air scouts and patrols, further limitations are placed not only upon the use of the periscope itself, but on maintaining the ship at deep depth by use of slow speed. Early submergence to avoid being sighted on the surface is essential, particularly near bases and ahead of large formations. The chances of the submarine sighting the plane first and escaping discovery by diving is much less when the type of plane to be encountered is fast and small. Patrol type planes, although they have ample speed, are usually visible much farther than small observation planes. Clouds and ceiling may work adversely against visibility from the plane, but there have been instances in the case of large cumulus clouds where planes have been able to hover undetected and observe opposing forces. If mere knowledge of presence is to be a consideration, the fact must not be disregarded that absence of the close approach of the plane does not indicate necessarily that submarine on the surface has not been observed and reported. If absolute security against detection is to be maintained under conditions where it is possible to encounter aircraft, the only safe means of accomplishing this is to remain submerged below 100 feet during daylight hours. Submarines are sighted from planes not only as a result of wakes, slicks, and feathers, but also by sighting the outline of the hull either from the dark green shadow cast or by color contrast due to growth at the waterline, turbulence and light-colored objects about the ship. Sides near the waterline must be kept free from marine growth. Submarine decks must be kept the same color as the sides in order to avoid a contrast which will facilitate discovery by planes when the submarine is on the surface at night. The larger the submarine, the closer the main deck is to the surface, and the higher the speed the more easily the submarine may be picked up from the air under any condition. In bright sunlight and with smooth sea, submarines are more readily discovered than when it is overcast and the sea is choppy. Unless some obviously poor periscope handling has already revealed the submarine's presence, the aircraft pilot or observer who is particularly adept at picking up submarines usually has his eye first attracted by a small spot of lighter color than the surrounding sea, and this is frequently out of the corner of his eye, as with picking up lights on the horizon at great distances. Under ideal conditions in tropical waters with bright sunlight, submarines can be sighted at depths down to at least 20 feet. The aircraft does not have to pass directly overhead to sight the submarine when the sea is calm. Cloudiness, whitecaps, and more nearly opaque temperate waters serve to reduce possibilities of detection, but there are no conditions under which the submarine can afford to completely disregard care and caution in avoiding menace from the air. Submarine officers should avail themselves of every possible opportunity to observe craft similar to their own from the air under various conditions so that they will fully realize the possibilities of detection under similar circumstances. Any procedure such as flooding tubes through the muzzle doors, which will permit the escape of air bubbles, must be avoided when air patrols are in the vicinity. For successful operations in the vicinity of aircraft, the submarine must be adept at changing from periscope depth to deep submergence, and vice-versa, accomplished in the minimum of time and this minimum at slow speed.

4404. Adherence to the following procedures will reduce possibility of detection from the air:

      1. Maintain a keel depth of not less than 140 feet except when it is necessary to use the periscope for observation.

      2. Refrain from pumping bilges to sea or blowing heads or sanitary tanks while submerged during daylight. Bilges must be pumped to compensating tanks. Heads should be pumped with hand pumps.

      3. Conning officer should make periodic observations through periscope for air leaks.

      4. When circumstances permit, go from periscope depth to deep submergence at slow speed using a small angle to avoid showing a propeller wash. If quick deep submergence is necessary, negative tanks should be used.

Section 5
Daylight Attack By Single Submarine

4501. The attack itself commences when the submarine has reached a position within effective torpedo range of the objective and terminates with the firing of torpedoes. The attack should be conducted by aggressive tactics and by employing the same methods used as in the approach to avoid detection.

4502. Whether the attack will be conducted by periscope or sound, or both, will depend upon the weather conditions, type, disposition, and tactics of screens, and number, disposition, and maneuvers of the enemy target.

4503. During the attack phase, the submarine commanding officer must be prepared for any eventuality so that no maneuver of the enemy will deny an opportunity to fire torpedoes. He must be ready to go deep to avoid being rammed, intentionally or inadvertently, and yet be able to fire by sound.

4504. A commanding officer of a submerged submarine must assume that a critical situation exists when he finds his vessel in a sector on either bow of a ship and within such a radius, at the relative speed of approach obtaining, that danger of ramming exists before he can increase depth. In these circumstances, having due regard to distance from enemy track, speed of enemy, estimated time since last change of course of hostile ship, factors affecting the rate that depth can be increased, and any other special conditions, a submarine commanding officer shall not hesitate when he considers it necessary for the safety of his vessel, to go immediately to deep submergence.

4505. Multi-speed torpedoes should be kept set continually to the highest speed which will reach the target under the conditions existing.

4506. Torpedoes should be carried to such a firing position that they may reach the target at the highest torpedo speed setting and with such a short torpedo run that the target cannot avoid the torpedoes, but not so close that the torpedo will not settle to its set depth (See paragraph 4613). This also affords the greatest natural coverage of errors. Since close attack also increases the chances of detection and consequent destruction, the commanding officer must weigh thoroughly the advantages of close range firing as compared with firing at the first suitable target within range of his torpedoes.

4507. The depth setting of torpedoes will depend upon the type and draft of the target and the type of exploder mechanism of the torpedo.

4508. The best time to fire within effective range is as soon after a change of course by the target as the control problem can be worked out.

4509. The best chances of hitting are with small gyro angles.

4510. Small and large parallax shots, when it is necessary to use large gyro angles, or when accurate ranges are not obtainable, present reduced chances of hitting. In addition, small parallax shots from bow tubes and large parallax shots from stern tubes lengthen the attack and thus increase chances of discovery. However, for sound attacks, these forms of fire have certain advantages and also place the submarine in good position to maneuver subsequent to attack.

4511. Track angles will be chosen to provide the best chances of hitting, considering the amount and direction of the most probable errors in estimating enemy courses and speed and the probable maneuvers of the target to avoid, and to afford a firing position best protected against discovery or ramming, and best calculated to facilitate escape.

4512. The minimum spread used should cover at least 80% of the target length.

4513. Firing torpedoes on different tracks to hit the same point of a moving target is not considered firing a spread. A spread is fired only when the torpedoes are aimed to hit at different distances from the same point of aim.

4514. In countering change of course of the target just before firing, maneuver the torpedo (by change in gyro angle) or shift from bow to stern fire (or vice versa) rather than maneuver the slower moving submarine. If in firing position, accept the change in track angle and fire on bearing with periscope angle corrected for the new track angle.

Section 6
Tactical Procedures of the Normal Individual Attack

4601. The submerged approach consists of the maneuvers that a submarine makes in attempting to gain most favorable position for firing torpedoes at an enemy target. The attack itself consists of the maneuvers from this point until torpedoes have left the tubes and are on their way toward the target. Once established in the desired scene of war operations, our older submarines are offensively as potent as the newer ones. As long as defensive and offensive surprise rests primarily in submergence, the facilities do not become out of date with submarines as with other weapons of other types. Tube for tube, the older submarines have nearly as much offensive power as the newer ones. With lack of modern instruments, correct procedure is more important in the older types, but it must be remembered that with perfection and installation of modern instruments the data automatically obtained from them can not be expected to be of increased value unless fairly accurate and correct data are put into the instruments. In contrast to other types of war vessels, the success of the submarine attack is dependent upon the commanding officer alone, provided he is ably supported by his organization and that it is well trained to function and serve his approach and attack methods. Unless the commanding officer of a submarine is an efficient and aggressive approach officer, the submarine is not dangerous to the enemy.

4602. Doctrine, definitions, and some procedures for approach and attack are contained herein. Type procedure is contained in the Manual of Interior Control (F.T.P. 98). Whether for individual or coordinated attack, procedure of the individual submarine is the same, except in the latter case, maneuvers are in some instances more restricted. Current doctrine for submarine approach and attack specifies that this be accomplished aggressively. This means that the approach officer places his vessel in a favorable position for attack at close range undetected and in as short time as possible. This normally calls for a driving in approach where the angle on the bow is small, and assuming the collision course at highest practical speeds as long as it remains large.

4603. 1. Standard commands for torpedo control are essential for the same reasons as other types of standard phraseology and the following are prescribed:

         1. "Make ready the (bow) (stern) tubes." This orders all designated tubes flooded and made ready in all respects for firing. Only certain numbered tubes may be designated if desired.

         2. Set gyro angle(s) _____ degrees." Specific angles are ordered for individual tubes when necessary. This order is used when ships are not supplied with, or are not using, the automatic or "follow the pointer" angle-setting equipment. The order provides for relative settings being received in the torpedo rooms so that necessity for conversion by the torpedo personnel is obviated.

         3. "Set spread angle _____ degrees." this orders spread angle to be set when using divergent spreads on submarines equipped with and using the automatic or "follow the pointer" gyro-setting equipment.

         4. "Out gyro spindles." Used when automatic disengaging feature is not installed.

         5. "Order of firing (giving numbers of tubes in desired sequence)."

         6. "Standby." This is used as the preparatory order for firing and should not be appended by the words "to fire" in order to obviate the contingency that the latter only is heard and the torpedoes are fired prematurely.

         7. "Fire _____ (number of tubes)."

      2. On modern submarines the above is varied as follows:

         1. "Make ready tubes no. _____".

         2. "Set depth _____ feet".

         3. "Order of tubes forward (aft) _____".

         4. "Gyros cut in forward (aft)".

5. "Standby forward (aft)".

6. "Final set-up".

7. "Final bearing".

8. "Fire one" etc.
3. It is important to avoid confusion that, during the approach and attack, a definite order is followed in which the ship's head, target bearing, angle on the bow, range and other attack data are given.

4. Observe gyro angles closely. Keep the C.O.informed of gyro angles. when gyro setters are energized get a mark between T.D.C. and torpedo room.

5. Check "gyro angle set" lights prior to firing.
4604. Doctrine prescribes that when a choice can be made without jeopardizing their effectiveness, the approach and attack are made with wind and sea astern, from direction of the sun, on the side away from the moon, with the target silhouetted against rising or setting sun and on the side least protected by screening vessels. Except for the last which is obvious in itself, these considerations are amplified and explained as follows:

      1. With the wind and sea astern, the periscope is more difficult to detect due to little or no spray and reduced feather and wake effect. Lookouts from enemy ships are not as efficient when looking into the wind. In a heavy sea, more speed will probably be required to maintain depth control, but under these conditions, discovery of periscope wake is almost impossible regardless of speed. In cases of extremely heavy seas or long ground swells, the commanding officer must give consideration to whether or not the attack is best executed from periscope depth or on generated bearings or by use of sound equipment from deep submergence.

      2. If the sun is behind the periscope and at an altitude of 45 degrees or less, the bright sun outlines the enemy more clearly and estimation of course and speed are favorable to the submarine. Also, under these conditions, the periscope is most difficult for enemy lookouts to detect when looking directly into the sun.

      3. During low visibility, the periscope is usually most effective in low power with the conning tower darkened. If attacking submerged during twilight, better vision is obtained when looking in the direction of the moon or of the sun just before rising or after setting.

4605. When on war patrol, it is standard procedure to carry all torpedo tubes loaded with torpedoes fully ready. Torpedo fire-control facilities should be kept in the state of readiness compatible with that of the torpedo armament itself. The tubes themselves are prepared for firing with the exception of flooding and opening impulse air stop valves. Current doctrine prescribes that at night or in low visibility during daylight, except when conducting training exercises at sea, all tubes in each nest are kept fully prepared for firing except flooding the tubes and opening outer doors (see paragraph 1131). Depth setting should be as required for the expected target, and gyro setting should be on zero with spindles disengaged except for those ships which have automatic retracting devices. As soon as conditions permit, torpedoes which have been in flooded tubes should be withdrawn and inspected, after which, they are again sealed in the tubes. At least one complete reloads of "fully ready" torpedoes is maintained in the racks with remaining torpedoes in an advanced stage of adjustment. After an extended war cruise, all unfired torpedoes will be taken to the base or tender for examination and adjustment. Submarines will, in all probability, be loaded from the base or tender with a minimum of "fully ready" torpedoes sufficient to load all tubes. "Fully ready" torpedoes must be checked in accordance with current instructions.

4606. At all times tube control stations necessary for firing are manned, and it is normal procedure to have them combined with the ship control stations.

4607. The organization for battle stations submerged provides adequate personnel to perform the following duties:

      1. Supervision and preparation of tubes for firing.

      2. Setting of gyro angles and spreads as directed by control.

3. Setting of torpedo speed and depth as directed by control.

4. Venting of tubes inboard where poppet valves are not installed and preparation to fire by hand should this become necessary.

5. Making final last minute adjustments to torpedoes in racks in order to be prepared to perform reload expeditiously after firing.

6. Manning of all sound equipment which can be used in the approach with best talent available.

7. Rapid and infallible interior communications.
4608. Standard procedure provides a control organization capable of obtaining data for conducting the approach and attack and determining the torpedo firing data. Personnel of the organization are so trained that they can interchange positions and duties. This serves the dual purpose of providing for casualties and to enable the control party to function more intelligently by virtue of being able to visualize the entire picture of the approach and attack. Duties of individuals of the control party will vary according to the type of control equipment provided and the number of officers available. The following are essential functions of the control party:

      1. Observe screening vessels briefly for the purpose of avoiding them and observe the target to determine bearing, range, angle on the bow and estimated speed and, on occasions, to note changes of target course.

      2. Determine target course; distance off target track; range; various combinations of own course. Track angle; and gyro angle for situations existing, anticipated, or planned; expected target range and torpedo run; and spread angle.

      3. For the particular attack and target, determine volume of fire, whether or not divided fire is in order, torpedo speeds and depth settings, track angles, gyro and spread angles, torpedo run and identity of target if silhouettes are available.

      4. Determine firing intervals, firing bearings, speed corrections for depth, parallax corrections, and sound firing bearings.

      5. Operate periscope control switches as directed by the approach officer. Operate battle order transmitter and firing key.

      6. Transmit orders and record data and times primarily for plotting purposes.

      7. Utilize sound equipment to fullest advantage to obtain target data and to avoid screening vessels.

4609. Normally the control party comprises the following:

      1. The commanding officer, as approach officer, stationed in conning tower or control room at highest periscope.

      2. Executive Officer as assistant approach officer.

      3. One officer as T.D.C. operator.

      4. Engineering officer as diving officer maintaining depth control.

      5. One officer as Mk. VIII angle solver operator and assistant on T.D.C.

      6. One officer to maintain the plot.

      7. One officer in each torpedo room. (If available).

      8. Radar operators, talkers, fire controlman, recorders, sound operators, as required.

4610. The following items of control apparatus and aids have been developed to expedite calculations and minimize errors in the solution of the mathematical computations incidental to the approach and attack:

      1. Submarine attack course finder.

      2. Mark 1 angle solver (for straight shots).

      3. Mark 6 and Mark 8 angle solver.

      4. Torpedo data computer.

5. Tube nest indicator.

6. Periscope stadimeter and telemeter scale.

7. Periscope stabilized azimuth.

8. Range-keeper.

9. Telemeter range table or slide rule lor range omnimeter.

10. Distance to track table (or slide rule).

11. Azimuth line--speed table.

12. Spread tables.

13. Voge diagram.

14. Speed--distance--time tables.

15. Speed correction tables for depth.

16. Firing interval table.

17. Stop watch.

18. Plot.

19. Speed vs. RPM and draft tables of enemy's vessels, if available.

20. Parallax tables for sound firing except on ships equipped with sound bearing converter.

21. Submarines equipped with Torpedo Data Computer and automatic gyro setting--Target bearing transmitter for firing straight or curved shots in surface condition at night or during reduced visibility. Other submarines--night pelorus.

22. Sound equipment.

23. Radar.

All, or only a portion, may be available to the individual submarine, depending upon type, space, and personnel available. It is categorical and it must always be borne in mind that most instruments, including the modern automatic ones, are dependent upon estimated data and such instruments in themselves cannot rectify personnel errors. For the successful approach against unfamiliar targets, the seaman's eye still remains a most valuable adjunct and the experienced approach officer will instantaneously detect any significant errors in his final setup.

4611. The above instruments and aids are used to determine and apply the following information obtained from periscope observations, radar, or sound equipment:

      1. Bearing of target, by periscope observation, radar or sound equipment.

      2. Course of target, by estimated angle on bow, relative and true bearing of target, using attack course finder.

      3. Range to target by periscope telemeter or stadimeter, radar, or echo ranging.

      4. Speed of target by plot, either manual or automatic. Speed estimates by plot are adjusted or confirmed by estimation of bow waves and stern wakes, smoke, and general knowledge of tactical situation and type of target. RPM turn counts determined by sound operator, although not to be used conclusively, are valuable in assisting estimations of target speed and changes of speed. The range-keeper and torpedo data computer are of value in assisting speed estimate by analyzing changes in range and bearing of target. Estimating speeds from other vessels in formation may be useful, but must be used with

caution. If enemy system of visual speed indicators is observed and analyzed, circumstances permitting, this information should be disseminated to other submarines liable to make contact.
5. Distance off track tables or slide rule entered with angle on bow and range.

6. Volume of fire and depth setting of torpedoes, determined by circumstances guided by doctrine, advisability of divided fire, type of target, type of exploder.

7. Point of aim, rifle principle at center of target for close range, periscope firing when data can be expected to be accurate and discovery has not caused target to maneuver to avoid. Spread when, and in manner, called for by the specific situation under other circumstances.

8. Spread angles, determined from spread tables with entering arguments of torpedo run and difference in gyro angles.

9. Firing interval, determined from firing interval tables which are gyro angle tables for firing salvos with proper interval when torpedoes are all fired to hit the same point of aim, or firing interval diagram.

10. Torpedo speed correction for depth, determined by table or diagram.

11. Track angle, determined by attack course finder or torpedo data computer.

12. Gyro angle for desired track angle, determined by attack course finder.

13. Predicted run of torpedo, estimated from plot or determined from Mark 6 or Mark 8 angle solver.

14. Periscope firing bearing, determined by angle solver or torpedo data computer.

15. Sound firing bearings, periscope firing bearings as obtained, corrected for parallax of point of aim and propeller sounds and offset of sound projector from periscope by parallax tables or computed by the sound bearing converter or torpedo data computer. Sound bearing converters eliminate necessity for use of parallax tables.

16. Generated firing bearing, continuously determined by torpedo data computer for either periscope, radar, or sound firing bearing. In ships fitted with torpedo data computer and tubed nest indicators, the gyro angle, track angle and torpedo run are continuously being computed for the existing situation of bearing of target, range of target, own course and speed, and enemy course and speed. The computed gyro angle is set on the torpedo continuously either automatically or by follow the pointer, spread angles being superimposed as desired.
4612. Doctrine prescribes use of the highest torpedo speed which will reach the target under conditions existing. The only conditions when lower speed settings would be used are against large formations when it is seen that it is impossible to close to favorable attacking position, and against anchored targets when conditions prevent closing to short range, and on torpedoes prepared for circular run. High speed is essential in a torpedo in order to reduce the time required to cover the distance from submarine to target; the higher the speed, the less time elapses, and consequently the target has less time to maneuver to avoid. Submarines firing by sound from deep submergence and using Mark 6-1 exploder mechanisms should set torpedo depth to hit target.

4613. Current doctrine for approach and attack provides that the latter be executed at the shortest possible range consistent with chances of discovery, insuring that torpedoes are at set depth, to take advantage of greatest coverage of errors, and to permit target least time to maneuver to avoid torpedoes, or ram. With marks 10, 11, 14, and 15 torpedoes and modifications, and with Marks 3, 4, 5, and 6-1 exploder mechanisms, this minimum range is currently 500 yards.

4614. The volume of fire will depend upon the importance of the target, its life in torpedo hits, whether a spread is necessary, the type of torpedo fire, the number of tubes installed, the supply of torpedoes on hand or available at the base, and whether reduction in strength

or reduction in speed of the enemy is desired. Sufficient torpedoes should be fired to destroy or seriously cripple the enemy ship. Serious damage to one ship is generally preferable to moderate damage to one or more. If necessary to fire at other than an individual ship target, shoot all loaded tubes. The following table is to be used as a guide:

Target	Life In Torpedo Hits			Required No. Torpedoes To Insure Sinking Target. 50% Hits With Spread			Recommended Volume of Fire With Spread
BB, CC		7			14			10	(all tubes)
Large CV		5			10			10
Small CV		3			6			6
CA, Large CL		3			6			6
AV, Large Aux., Med. CL, Merchant, Small CL, Small Aux.		2			4			3	or 4
DL, DD		1			2			3
SS		1			2			3

NOTE:-- The above table is simply a guide and is in no way mandatory. It is the opinion of most submarine officers that any combatant ship is worth a full nest torpedo salvo. It is also a known fact that in areas normally low in ship contacts, a submarine is justified in firing sufficient torpedoes regardless of target to cause a sinking. In like manner, in an area where targets are known to be numerous Commanding Officers must use their torpedoes with discretion and care in order to inflict the utmost damage to the enemy.
4615. Volume of fire is subject to considerable variation due to circumstances. Expected life of prospective target in torpedo hits is a variable quantity, depending on where hits are made--in machinery spaces, in vicinity of propellers, under magazines, whether ship is cruising or at anchor, how unexpected the attack, etc. Serious damage to one target is preferable to moderate damage to two or more. Some circumstances, particularly just before main engagement and if the attack is close enough to be certain of success, may dictate divided fire in an effort to reduce speed of the entire unit. Some circumstances, for example, a coastal patrol submarine with rare opportunities for attack, might demand firing a full nest of torpedoes on a spread at an enemy submarine approaching one of our main bases. On the other hand, if circumstances indicate the necessity of conserving torpedoes for probable future contacts with primary objectives, minimum expenditures or none at all may be made on secondary targets. In other words, current doctrine with regard to volume of fire may be modified by:

      1. Whether primary objective or not.

      2. Whether primary objectives are definitely out of reach of attack.

      3. Special importance of target for political or economic reasons.

      4. Number of targets available.

      5. Number of torpedoes remaining for reload.

4616. When using Mark 3, 4, and 5 exploder mechanisms, torpedoes are set to hit below the armor belt of armored targets. In absence of specific information regarding the particular target and when using these types of exploder mechanisms, it is standard procedure to set torpedo depths as follows:

      1. For BB's, CC's -- 20 feet.

      2. For CA's, CV's, large auxiliaries, transports, and merchant ships -- 12 feet.

      3. For CL's, small auxiliaries, transports, merchant ships, and SS's -- 10 feet.

      4. for DD's -- 6 feet.

      With the above exploder mechanisms for night firing, depth settings are kept at a minimum for expected targets unless (and until) target is identified.

4617. When using the Mark 6 exploder mechanism set torpedo depth in accordance with the latest instructions from the Force Commander.

4618. Selection of straight or curved fire may be forced by circumstances outside the control of the approach officer. The torpedo, in lieu of the submarine, must be maneuvered to satisfy rapidly changing situations. Straight (or nearly straight) torpedo shots should always be chosen when firing by periscope or generated bearings from recent periscope observations when adequate time and room for maneuvering exist and when required volume of fire is small enough to permit. Target practice results throughout the years confirm the fact that the straight shot is the better shot when feasible. Advantages and disadvantages of straight (or nearly straight) fire are:

      1. Advantages:

         1. Accurate torpedo tactical data.

         2. Small likelihood of torpedo course error.

         3. Error in torpedo run has little effect on control problem.

         4. Length of torpedo run has small effect on control problem.

         5. Simple control problem.

      2. Disadvantages:

         1. Requires considerable time and room to maneuver for submarine having bow tubes only.

         2. May result in long range shot if restricted as to whether bow or stern nest is used.

         3. May require considerable waiting for target to come on line of sight, but less so than with small parallax shots from bow tubes or large parallax, from stern tubes.

         4. May permit firing of only one tube nest.

4619. (1) Angled shots should be chosen when:

      1. Target maneuvers shortly before firing bearing is reached and it is necessary to change track and allow time for new setup.

      2. Circumstances are such that maneuvering for straight or small angled shots would jeopardize or prevent the attack.

      3. Firing small parallax shots on listening bearings.

      4. When necessary to obtain required volume of fire.

      (2) Advantages and disadvantages of angled shots are:--

      1. Advantages:

         1. Permits shortening time for target to come on firing bearing when firing large parallax from bow tubes or small parallax from stern tubes.

         2. Requires less time to shift track angle for favorable shot when target makes last minute change of course.

         3. Permits firing from almost any position relative to target having favorable track angle.

         4. Permits maneuverability for safety while retaining power to strike.

         5. Especially desirable for firing on listening bearing.

         6. Permits firing both tube nests simultaneously or as nearly so as desired.

      2. Disadvantages:

         1. Complicated control problem.

         2. Available torpedo tactical data not too accurate or consistent.

         3. Possibilities of torpedo course errors.

         4. Allowable error in estimated torpedo run is small for short ranges.

         5. Short torpedo run makes control problem more difficult.

(3) When large angled shots are required by the exigencies of the situation, the types chosen which will insure successful, undetected, close range firing of torpedoes so that they will hit the target. Considering risk of discovery with resultant possible evasive tactics and reduced chances of hitting, the following order is to be favored in choosing large or small parallax shots:

1. Stern tube -- Small.
2. Bow tube -- Small.
3. Bow tube -- Large.
4. Stern tube -- Large.

In general, except when necessary volume of fire requires it, avoid large angle, large parallax shots. This type of shot requires accurate data to hit and is a poor wartime shot for it must be made from a position vulnerable to detection.

4620. Track angles should be chosen to provide best chances of hitting, considering the amount and direction of the most probable errors in estimating enemy course and speed, when such choice does not jeopardize chances of executing the attack. In addition to this, where there is any latitude in the choice of firing position, consideration must be given to possible maneuvers of the targets, position and possible maneuvers of screening vessels, best position to avoid discovery, ramming and depth charge attack, and easiest position from which to start retirement or another attack, should multiple targets be present. In general, track angles less than 90° permit earlier firing and therefore, less chance of being discovered. Track angles greater than 90° give better protection against ramming, afford more coverage of course errors and maneuvers of the target to avoid torpedoes, and facilitate escape. Ninety degree track angles are best for hitting the target when both course and speed have been accurately determined. One essential consideration for submarine torpedo fire is that the torpedo run be the minimum possible down to the 500 yard limitation. Minimum run to target gives minimum opportunity to avoid. Errors in lateral distance at the intercept point increase rapidly with increase in time of torpedo run. For a constant speed torpedo and correct course estimate, the allowable enemy speed error is inversely proportional to the time of torpedo run to target track, or in other words, the shorter the torpedo run, the larger the allowable enemy speed error. The most desirable track angle is that in which the target course is perpendicular to the firing bearing, or in other words, when submarine is exactly abeam of the target. For this optimum track, considering course errors only, some sacrifice is made in that the torpedo run is lengthened, and the greater the enemy torpedo speed ratio, the greater the increased torpedo run. Track angles between 70° and 110° are considered best for all around coverage. However, when in favorable position to fire, adjustments of course or gyro angles for changes in track angles should not be made if they will delay getting off the shot. When they delay getting off the attack, too much consideration must not be given to choice of track angles, particularly on a long target at close range. When distance off track is less than 500 yards, it will be necessary to choose small or large track angles in order to obtain necessary torpedo run. If a choice is permissible, in a heavy sea, choose such track as will permit torpedoes to run parallel to the sea or at right angles to its direction.

4621. Spreads are always used.

4622. The minimum spread should cover at least 80% of the target length. Even this is considered to be small spread, where the range and track are most favorable and the target speed, course, and range are accurately known. This would insure a high percentage of hits under these conditions. Normally these data are not too accurately known and spreads to cover as much as 200% of the target length should be fired, depending upon how well the problem is solved. When using any spread, sufficient torpedoes should be fired to ensure the number of torpedo hits necessary to sink the target.

4623. Parallel spreads can be fired only from submarines having both bow and stern tubes.

4624. Various spreads are fired using the following procedures:

      1. Divergent spread is obtained by using spread angle or by swinging the submarine. The use of the latter method is less desirable than the former because of the lack of control and the possibility of missing shots. The divergent spread is simple to accomplish

with modern gyro setting mechanisms. It is more difficult to evade than the longitudinal spread. Divergent spreads require rapid calculation of spread angles which are subject to error unless torpedo run is accurately known.
2. Longitudinal spread is obtained by firing all shots in succession with parallel tracks with the same gyro angle, using different points of aim on the target. Longitudinal spread is the simplest to apply of all spreads and is used principally with periscope firing. An advantage of the longitudinal spread is that spread density is not dependent upon torpedo run.

3. Parallel spreads consist of simultaneous fire from each nest with supplementary and opposite gyro angles. The torpedoes from each nest are separated by the distance between nests plus the sum of torpedo advances. This type of spread is undesirable because of the large gap between the torpedoes from bow and stern nests. A special circumstance might make it useful against two ships of the same formation. Parallel spreads and the reasons for not using them under other than exceptional circumstances, are not to be confused with simultaneous fire from each tube nest with high angle gyros, wherein the torpedoes do not follow parallel courses.
4625. Procedure for tactics of the approach and attack must be based on the assumption, until definitely established otherwise, that the enemy will be:

      1. Zigzagging at moderate to high speeds.

      2. Protected by aircraft and surface screens, the latter equipped for listening or echo ranging, or both.

      3. Ready and alert to maneuver to avoid submarines or torpedoes sighted or otherwise detected.

4626. To await visual contact requires unusual diligence on the part of the lookouts under most conditions of expected enemy alertness. Normally, when in the vicinity of formations and primary objectives, it can be expected that the submarine will be forced down by air patrols long before visual contact is possible. One exception to this, which makes for an ideal situation, occurs in cases of contact at, or just after, dawn if the service of information and circumstances during the night have permitted surface running and enabled the submarine unit to arrive at a position within a few miles ahead of the enemy and close to his probable track. The approach begins with visual contact with the target or advanced screens and continues until the attack starts. The object of the approach is to conduct the submarine, under restrictions of avoiding discovery by judicious use of periscope, speed, depth and course under the principles given heretofore, so that she will arrive at a position ahead of the enemy target. Then, with normal expectations that the enemy will continue his base course, he cannot escape attack if detection is not effected. The submarine then pushes home the attack to a position from which the torpedoes are launched and such that it will be impossible for the enemy target to avoid regardless of maneuvers he may make. The opportunity to make the approach will probably not be given by the enemy if discovery is effected before submergence. On the other hand, the opportunity to make the approach will not be presented unless the submarine reaches a position ahead of the enemy. Hence, a certain amount of judgement is necessary to determine the extent to which surface running can be resorted to in adjusting position. High surface speed works to the advantage of the submarine in these situations. If unable to reach a position ahead of the enemy, correct procedure is to take up station in an area he is expected to pass through, or to trail so that attack may be made in the event he should reverse course. When endeavoring by running submerged, to reach position ahead to start the approach, unless the target is a primary objective, conserve sufficient battery to remain submerged during the remainder of daylight and to get clear after the attack. During the early stages of the approach, if other submarines are in the vicinity, endeavor to make contact report. In doing so, do not jeopardize the success of the approach and attack by maneuvers which may lead to discovery, unless the primary task is information.

4627. If the first vessel sighted develops to form part of an advanced screen, penetrate or flank it in an endeavor to reach a position astern of the center of the screen.

4628. From this position, the submarine proceeds on the reverse course of the screen until contact with the enemy target is made. If, at this point, enemy course is undetermined, head toward the target and ascertain whether bearing is changing to right or left. Then, endeavor to gain a position in an area ahead of the target. This is accomplished by first turning about 40° to the side toward which the enemy's bearing is changing. This course is continued at speeds and depths commensurate with the situation until the inner screen, if present, comes into view.

4629. The approach officer determines the enemy course as soon as practicable and, if the angle on the bow is zero, the correct procedure is to continue heading toward the target. If the angle on the bow is 15° or less, head 30° to 45° ahead of the target and continue closing. If the angle on the bow is more than 15°, assume normal approach course in order to get ahead of the target.

4630. With due consideration to enemy's base course and changes of course due to zigzagging, an advantage accrues in reaching position ahead, as quickly as possible under the circumstances, in that during the later portion of the approach and during the attack, slow speeds may be utilized minimizing danger of detection and permitting full use of own sound equipment. In case the inner screen is not patrolling its station, it may be assumed to be a sound screen. If observed to patrol at high speeds, it can be assumed to be most probably not a sound screen. Early differentiation between zigging screens and patrolling screens should be made since this has considerable influence on the conduct of the later stages of the approach and attack.

4631. The amount of high speed running during the approach and attack is influenced by the situation, the remaining power in the storage battery, the remaining hours of daylight, the probable retirement requirements, and the necessity for clearing the area rapidly to get out contact reports. Under normal procedure, these become secondary if the target is an enemy heavy ship, except when information is essential to furtherance of the general plan.

4632. During the conduct of the approach, consideration is given to the desired heading for the attack. If possible, the submarine is steadied on this course before the attack position is reached. Depending on the necessity of penetrating an inner screen, or on the anticipated amount of the next expected course change of the target, a decision must be made before reaching the attack position whether to use straight or angled fire, and in the latter case, whether it will be small or large parallax. This decision is governed by the situation existing, and is influenced by the required volume of fire and whether bow or stern fire is desired or optional. When necessary volume permits, the simplest attack is the normal approach for bow tube fire. Speed up to close the target if it changes course away; cross over and fire with stern tubes if the course change is toward, which course change places the submarine too close to the target's track.

4633. When the predicted run of a torpedo is not accurately known, particularly at ranges under 1500 yards, large gyro angle shots are undesirable. At longer ranges, the error in estimated torpedo run becomes minimized, because the average torpedo speed over the entire run reaches a nearly constant value.

4634. If conditions permit, and in order to avoid firing on a knuckle when using periscope firing, torpedoes should be fired as soon as possible after the commencement of a new leg of a zigzag. This is most easily accomplished by increasing or decreasing the track angle.

4635. The proficient approach officer is prepared for last minute maneuvers on the part of the target. If the change in course is not too great and a track angle has been selected which gives good coverage for errors, accept the change and fire without change in set-up. When coming in to the attack position, the approach officer should know approximately how much the average expected change of course toward or away will throw torpedoes ahead or astern of the point of aim and adjust the latter accordingly when he finds he is firing on a knuckle, particularly when firing a longitudinal spread.

4636. Submarine approach and attack cannot be conducted under precise stipulations. The enemy movement and his screens, and the varying situation as seen by the approach officer at each periscope exposure, affect the decision as to form of attack and firing range.

Target speed exerts considerable influence upon the tactics of the approach. If known to be of low or moderate speed, the correct procedure is to head for the target and close the range as quickly as possible, commensurate with the distance off the track. If of high speed, the primary consideration is to get ahead and then allow the target to do the closing of the range.
4637. (a) Approaches against targets well protected by surface and air screens may have to be conducted from deep submergence, especially in the latter stages. The approach and attack from deep submergence require the highest degree of coordination between the sound and torpedo control personnel. The best method of attack developed to date is to place the submarine on a course normal to the estimated base course of the target, which is approximately the reverse of the target's initial bearing, and to fire straight shots from the bow or stern tubes as the target passes the submarine's position. Success in this type of attack depends largely on the good judgement of the commanding officer in estimating the target course, speed and range from the information available to him. If good information on the target's speed has been obtained from periscope observations before deep submergence is necessary, the problem is much simplified. The amount of any speed change after deep submergence can be estimated by the change in propeller turn count. It must be borne in mind that no single sound bearing can be considered accurate. Ranges should be taken sparingly and by the single "ping" method. Spreads should always be fired to allow for errors bound to exist in the target's course, speed and range. Correction must always be made for the parallax between the target's propellers and the M.O.T., the parallax between the periscope and the sound receivers, and the change in bearing of the target from the time the sound is generated by the propellers until the torpedo is fired. These corrections are made by the Torpedo Data Computer, Mark 2 and 3 and by the sound bearing converter for vessels equipped with the Torpedo Data Computer, Mark 1.

      (b) The approach described in (a) above is not recommended except under the heaviest surface and air escort with the smoothest sea conditions. Under other conditions it is probable that the most likely and successful approach and attack will be made using the periscope carefully and sparingly and running at deep submergence between periscope exposures.

4638. (a) Whenever circumstances permit, after firing one tube nest, the submarine should be maneuvered to fire the other tube nest at the same or another target. The attack should be made if practicable.

      (b) Except under most favorable sea conditions, discovery at the time of firing torpedoes is almost inevitable. The submarine must resort to retirement procedure immediately after the attack and so continue at least until the reload is completed. Retirement procedure is a defensive action, but prolonged pursuit or certainly of successful depth charge attack by pursuers may warrant offensive action. Since evidence of the location of the firing point may continue for some time, that particular spot must be vacated immediately. Offensive action should be taken whenever practicable against escorts of such a size as to warrant torpedo fire. This may relieve or reverse a desperate situation. Retain the initiative by staying at periscope depth as long as practicable consistent with reasonable chances of escape. Necessity for prompt transmission of contact reports will also influence offensive action against light screening vessels. Follow the procedure given heretofore for avoiding supersonic and air screens during the retirements. If there is no further possibility of attack on primary objectives and if pursued by supersonic screens, seek areas with temperature gradients, or areas with backgrounds unfavorable for enemy sound detection, if such exist in the vicinity of operations. To escape from air attack alone, run at a safe depth below 100 feet at slow speed and cross wind. Make high submerged speed when propeller and depth charge noises of surface craft are greatest. Take advantage of wakes and under-running ships astern of the target.

4639. Reload all tubes that were fired as soon as practicable, in order to be ready for another attack if the opportunity is presented. If circumstances permit and require it, all reloads should be made below 100 feet. Follow necessary procedure to avoid leaving a bubble wake during the reload.

4640. The best training for proper procedure in the conduct of the approach and attack and in proper periscope handling, is afforded by practice approaches and battle torpedo practices. In addition, the frequent use of the attack teacher[^*] and drills of the entire control party in making quick changes in control problem set-ups will be found most valuable in enabling the party to visualize changing situations and to insure rapid and correct new solutions. Use of the attack teacher becomes valueless unless correct procedure in allowing for deceleration and brevity of periscope exposure is followed. Poor technique and bad habit, if allowed to develop in the attack teacher, will be continued at sea. Its use becomes most important when supervised by a capable observer who offers constructive criticism. The entire control party should be used in the approach at the attack teacher. In addition to its use for approach purposes, the attack teacher is most valuable in developing ability to obtain ranges and angles on the bow with the shortest possible exposures. This is accomplished by using various targets, ranges and angles, and by gradually decreasing exposure length -- timing them with a stop watch.

Section 7
Twilight Attack

4701. A submerged attack, just before evening or after morning twilight or during twilight, may offer excellent possibilities of success, particularly when the target is between the light and the submarine. In such a case, the approach is practically safe from detection. Pains should be taken not to get in too close, since distances usually are over-estimated under such conditions. Light is the determining factor in choosing the side for attack. If the submarine is on the light or unfavorable side upon contact, the submarine should cross the enemy bow if possible.

Section 8
Night and Low Visibility Attacks

4801. When sight or radar contact on a possible enemy ship is made go to stations for tracking immediately. Warm up all main engines and be prepared for flank speed. Track contact and determine his course, speed and disposition. The plans for the attack are dependent upon visibility conditions, time and locality. Remain on the surface, in order to maintain the advantages of mobility, until there is a possibility of detection. When detection is possible, go to radar depth. When target can be seen through the periscope clearly enough to make the attack, go to periscope depth and deliver the attack.

4802. While on the surface take into consideration all manners of possible detection, including silhouette, wake, smoke from engines, etc.

4803. Do not unduly delay the attack. It may be possible to make a series of attacks. Complete enemy convoys have been destroyed by one submarine in a series of attacks.

4804. Submarines have been sighted on bright moonlight nights at 12,000 yards range; and at radar depth submarines have been sighted at 4,000 yards. The possibility of the enemy having radar must always be considered.

4805. In bright moonlight a target at long range is farther away than is usually estimated; as range decreases it is usually closer than estimated.

4806. If the enemy consists of more than one ship, plot his disposition and endeavor to pick out the escorts, determining the type patrol the escort(s) is conducting. If any of the enemy ships are pinging have sound men keep on pingers. (They are probably escorts).

4807. In case of a contact at low range in low visibility, the O.O.D. Should act immediately in accordance with doctrine. The execution of the attack and diving the ship should be immediately carried out by the O.O.D.

4808. During night surface tracking, approaches and attacks, require lookouts to continue to search own sector.

4809. After attack is delivered take evasive action and prepare for further attacks.

4810. It is essential that the commanding officer should have very definite instructions for his officers of the deck and it is imperative that they use their initiative immediately in attack, using straight bow or stern shots where possible.

4811. Sight angles should be made up in advance for several possible conditions of range, track angle and speed, and memorized by the officer of the deck.

4812. Keep the torpedo data computer lined up ready for instant energizing with the following preliminary data:

      1. Input own course and speed automatic.

      2. Enemy speed 10 knots.

      3. Estimated maximum range of visibility.

      4. Target bearing set on zero and angle on the bow set on zero.

4813. Keep the announcing system energized with a microphone on the bridge.

4814. Supplement radar bearings with target bearing transmitter bearings.

Section 9
Attack On a Formation

4901. Such attacks generally differ from normal procedure against an individual ship in that there is choice of targets and the necessity of penetrating multiple screens.

4902. The selection of an individual ship as target should be governed by the following directives in order of importance:

      1. Choose a ship of the type designated by doctrine or otherwise as a primary objective.

      2. Choose the nearest suitable ship, or one in the nearest unit.

      3. Choose the leading ship of a column, or a flank ship in line or line of bearing.

4903. Fire at any suitable target rather than fail entirely to fire, provided such action will not frustrate your mission or that of other submarines in the vicinity.

Section 10
Tactical Formations and the Coordinated Attack

41001. These tactics are at present undergoing revision. They will be promulgated at a later date.

Section 11
Retirement

41101. Attack shall always be assumed to result in discovery at the time of, or shortly after, firing and procedure shall be regulated accordingly.

41102. Inasmuch as discovery at the firing point is practically inevitable, submarines must get away from the firing point as quickly as circumstances permit, having in mind that the use of high speed may not be warranted immediately.

41103. Use courses that will most quickly clear the counter-attacking vessels or enable them to be evaded without being detected.

41104. Take full advantage of the enemy wakes.

41105. High speeds should be used when the noise of enemy propellers, and depth charge and torpedo explosions are greatest; slow speeds should be used during periods of quiet.

41106. Utilize listening gear to the fullest extent for keeping track of the enemy pursuit.

41107. Reload all tubes that were fired as soon as practicable, in order to be ready for another attack, if the opportunity is presented.

41108. Keep the initiative as long as possible. At night or when the sea is rough, the torpedo wake is quickly obscured. If air screens are not present, the submarine commanding officer can act most intelligently from a knowledge of the actions of the escorts gained by periscope observations.

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Footnotes

*. [The "attack teacher" was a mock-up of a submarine conning tower and control room, used for training submarine captains and crews at the Submarine School at Naval Base, Groton, CT.]