Current Doctrine Submarines (USF-25(A))

Chapter I

Section 1
Basic Considerations

Foreword

    Doctrine may be defined as a compilation of principles, applicable to a subject, that have been developed through experience or by theory, that represent the best thought of the unit concerned, and that indicate and guide but do not bind in practice. Its purpose is to provide that understanding within a force that generates mutual confidence between the commander and his subordinates in order that timely and effective action will be taken by all concerned in the absence of instructions. It permits intelligent initiative on the part of the subordinate, the most desirable quality in all echelons of command.

  1. The fundamentals of Submarine Doctrine are derived from the War Instructions, U.S. Navy; General Tactical Instructions, U.S. Navy; Current U.S. Fleet Doctrine and Tactical Orders. Nothing in this publication shall be construed to conflict with the above basic instructions.

  2. The submarine is a weapon available to the naval command in the conduct of a campaign, designed and operated to attack or observe enemy surface or sub-surface craft without prior detection and without requiring support from other types. The essence of successful submarine attack lies in its unseen and unheard execution, resulting in surprise. The primary assets of the submarine are its ability to carry torpedo attacks to close range, objectively to point where enemy target can not successfully maneuver to avoid; to lay mines in waters controlled or under observation by the enemy where surface mine layers can not operate without hazard or detection; and to obtain positive or negative information regarding enemy locations or movements under conditions which take advantage of their inherent qualities. Any use of the weapon which does not take full advantage of these qualities when such are needed in the theatre of operations, is a sacrifice of available potentialities.

  3. During probable long periods before fleet action occurs, submarines may be usefully employed in the following tasks:

    1. Patrol. (Including commerce destruction).

    2. Scouting.

    3. Screening.

    4. Mining.

    5. Reconnaissance.

    6. Services to aircraft.

    7. Escort (under exceptional circumstances only).

    8. Delivering important mail or personnel.

  4. The primary task of the submarine is to inflict maximum damage on enemy ships and shipping. This task shall be carried out at every opportunity unless expressly forbidden. When submarines are used for scouting, observation, reconnaissance, etc., their operation orders should expressly state whether or not they are to attack.

  5. In battle, submarines initially unfavorably situated and not able to attain a favorable attack position, should be disposed in position to attack the enemy battle line upon reversal of the action, or to sink damaged enemy vessels left astern.

  6. In battle, submarines may, through threat or actual attack, serve as the anvil against which own battle line may attack the enemy battle line.

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  1. In the exercise of control of the sea or in defense of our own land positions, bases, and sea areas, the primary employment of submarines should be as patrol units for individual attack, and in the service of information, when this cannot better be performed by other types.

  2. Individual submarines, in order to be able to deliver their submerged attacks with full effect, must be so disposed as to permit freedom of movement within their own disposition and with minimum interference from own surface forces. Concentrated groups of submarines appear to be most effective against large convoys without air escort or when air escort is light.

  3. Submarines should not be employed in purely defensive operations for which surface vessels are equally adapted.

  4. In screening operations, submarines are suitable for distant screens only. If used as a close screen, they are, because of the potential necessity of submergence, liable to foul own formation.

  5. Attack by torpedo is the primary task of the submarine and main objectives are those enemy units most capable of inflicting damages to our own forces. Attacks on other types may be made when they do not jeopardize the opportunity to carry out the primary task. Submarines may carry both mines and torpedoes, or either.

  6. The most serious limitations of the submarine are: (1) vulnerability to damage from gun fire when in the surface cruising conditions and, (2) low maximum speed, low cruising radii and time endurance while submerged, coupled with the fact that usually several hours must be spent on the surface recharging storage batteries when the limits of this endurance are reached. Once a submarine has been located by the enemy, he knows the submarine cannot get very far away without coming to the surface.

  7. Those officers who are not thoroughly familiar with the type, when called upon to utilize or direct submarine operations, must guard against misconceptions as to capabilities or weaknesses which they may have gained through observing them under artificial or abnormal circumstances. Submarines may be able to execute assignments successfully in some geographical locations and weather conditions which would have been impossible of accomplishment under other situations. Conversely, failure to accomplish the mission in one instance must not be used conclusively in forming an opinion that the same assignment could not have been accomplished under more favorable circumstances for taking advantage of the inherent qualities of the submarine.

  8. There is probably no form of warfare in which the quick decision is more essential than in certain phases of submarine war; nor is there any form of warfare more susceptible to failure through mistakes, indecision, or hesitation on the part of the individual commanding officer. Full and complete service of information, coupled with anticipation and freedom to exercise initiative, is essential to the most effective use of the type.

  9. Under present limitations of communications while submerged and at low submerged speed, anticipation is particularly important to submarine operations with our own fleet against the enemy fleet. Once the submarine is submerged, these operations cannot deviate from a prearranged general plan and must therefore be conducted in accordance with doctrine. Once the plan has been put into execution, any extensive movement for adjusting position is impossible to accomplish. The weather-beaten canard the submarines are vessels of opportunity becomes a fact, unless opportunities are made and fully utilized in employing the inherent assets of the submarine. As long as the number of submarines available for use in connection with a fleet action remains limited, it is not enough to treat them merely as an intelligent mine field.

  10. The service of information must provide for furnishing own forces liable to make contact, with the location of friendly submarines. Instructions for submarines entering friendly waters must be explicit as to course to be steered and time to make rendezvous

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    with escort vessel; such instructions must be disseminated also to local defense forces at sea in that area. Except under very unusual circumstances, our own submarines may be expected to keep clear of friendly vessels and dispositions and will avoid areas occupied by own surface ships. If they should find themselves in the immediate presence of friendly surface craft, they may be expected to avoid revealing their presence. In this circumstance, if required to surface in an emergency, they will make emergency identification signals with the submerged signal gun. If able to make fleet speed, but not able to dive, our submarines may be expected to drop back into fleet formation or disposition for protection. Own submarines may be expected to keep clear of off shore areas during execution of sortie and entry plans. To do this, they must be kept informed of fleet movements.

  1. Submarine attack is perforce a single attack. Such attacks by two or more submarines may be coordinated when movements of the enemy are predictable or are restricted to narrow limits by other factors. These conditions are usually satisfied when it is evident that the enemy is approaching a specific objective. Such objective may be stationary, as when the enemy is approaching a geographical location in order to establish a base, or to attack one of our bases, or is returning to one of his own bases. Or the objective may be moving, as when the enemy fleet is approaching own fleet for attack. In these circumstances, coordinated attacks are necessarily from open formation. They resolve themselves into individual attacks by two or more submarines, when the submarine line covers a wide front normal to the enemy advance in order to provide for contingencies of freedom of enemy movement. If the enemy approach is positively known to be confined to narrow limits, the submarine line can then be parallel to the direction of advance, and the coordinated attack becomes a series of individual attacks. Using a submarine line normal to the line of enemy advance, has the disadvantage of offering comparatively few opportunities for attack. Using a line parallel to the advance, introduces the possibilities of no attack in case the estimate of expected enemy movement does not conform to the narrow limits needed for this type. In case sufficient submarines are available, combinations of the two systems may be used, or they may resort to a series of attacks under either system. It is axiomatic that the success of a submarine coordinated attack is dependent upon the service of information and the proper functioning of attack doctrine. To allow freedom of movement and initiative by individual commanding officers, the coordinated attack must be made from open formation. For communication purposes in the dissemination of information, it is desirable to retain a close formation as long as possible before deployment for attack. Hence, directives must permit sufficient time to assume the attack formation and for orienting lines and adjusting positions, if such become necessary. This points to the necessity for latitude in directives and encouragement of initiative in the echelon of submarine command. Submarine operations can be coordinated with, but not closely combined with, those of surface ships or aircraft. If such coordination is desired, slow submerged speed and lack of reliability in communications while submerged, place the burden of coordination on the other units involved, and this becomes too restrictive upon them. In advancing submarines on the surface during daylight, complete control of the air over them must be maintained in order to deny knowledge of their presence to the enemy and to prevent enemy planes from forcing them down, thus reducing speed of advance. When knowledge of their presence by the enemy is of no consequence, maintenance of surface speed can be accomplished by escort, either by own aircraft or by surface ships, with sufficient anti-aircraft protection. In cases where submarines remain on the surface under air escort, control of the air overhead by the escorts must be absolute. Otherwise, the submarines will be forced to dive to avoid both enemy and friendly planes due to the impossibility of differentiation at long ranges. If used in connection with fleet battle, a submarine losing contact, or a unit which definitely knows that the enemy fleet has gone by without presenting favorable opportunity for attack, may be expected to trail or to take position on the enemy's retirement line or between him and his most probable base.

  2. Although normally it is of primary importance that Submarine endeavor to carry out their operations undetected, contingencies may arise where it will be to the advantage of the O.T.C. that submarines reveal their presence to cause enemy confusion, or the avoidance by him of certain areas. Initiative, rather than directives, may dictate the use of this type of tactics.

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  1. If submarines performing reconnaisance or scouting missions take advantage of favorable opportunities for attack, this will reveal their presence and possibly jeopardize them in making contact reports. When attack is not desired, orders should so specify.

  2. In avoiding detection by aircraft, running deep, as well as the careful use of periscope, must be considered. If it is desired to conceal their presence, submarines should remain submerged during daylight hours, in areas exposed to air scouting by the enemy. Otherwise, a submarine should submerge at first sight of any plane. Small fast planes are hard to see, making submergence before detection difficult. Aircraft may pick up a submarine not only from wakes, slicks, and feathers, but from sighting the outline of the hull, even at considerable depth. In calm tropical waters with bright sunlight, submarines are often visible at depths in excess of 100 feet. In other waters, ability to see a submarine is greatly reduced. Overcast weather and many scattered clouds favor the submarine. Oil slicks, or air bubble slicks, not only reveal the presence of a submarine, but give its definite position.

  3. The development of supersonic sound equipment has increased the chances of detection of submarines by surface craft. Submarines will make every effort to attack without coming within range of a supersonic screen, but they can be expected to attempt penetration in order to attack enemy heavy ships. The performance of supersonic equipment is best in a uniform medium usually found well offshore in deep water with choppy surface. Poorest performances are obtained in coastal waters and are due primarily to the prevailing temperature gradients of the water caused by currents, tides, seasonal variations and the surface layers of a glass sea being heated by the sun. When it is necessary to penetrate a supersonic sound screen, the submarine may be expected to run as silently as possible at minimum speed with bow or stern towards screen so as to present the smallest possible target. Water conditions in the particular area of operations will be a guiding factor in evasive tactics. The opportunity to cross the wakes, or run under heavy ships, increases the chances of remaining undetected. In comparison with surface craft, except those especially designed, the submerged submarine is the perfect listening ship. Sound equipment and training of submarines should be developed so as to take full advantage of this factor and thereby convert listening equipment into an asset instead of allowing it to continue primarily as an anti-submarine device.

  4. The maximum surface speeds of our submarines are approximately as follows:

      O, R and S-type -- 11 knots.
      Narwhal (SS167) to Cuttlefish (SS171), incl., -- 16 knots.
      Porpoise (SS172) and subsequent submarines -- 20-21 knots.
      Barracuda (SS163) -- 9 knots.

    The above speeds can be made only if all the following conditions are fulfilled:

    1. All main engines in submarine developing full power on propulsion.

    2. Smooth sea.

    3. Clean bottom.

    4. Normal condition of loading (no reserve fuel on board).

    Actually a submarine rarely operates under all of the above conditions. For instance, engine power is limited to 80% of full power for normal cruising. One main engine must normally be reserved for the charging of batteries which reduces the number available to place on propulsion from 4 to 3 for four engine submarines and 2 to 1 for two engine submarines. In present day operations, submarines operate in the emergency surface condition, that is, with fuel ballast tanks full of fuel or water. Taking the above factors into consideration, the maximum cruising speeds we can expect from our submarines under average conditions of sea and bottom fouling are about 4 or 5 knots less than the maximum speeds listed above. Cruising ranges of all modern submarines are high, averaging about 12,000 miles. Surface speeds must be slow to realize these long radii.

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Image of chart: Maximum Time Submerged and Cruising Range vs. Submerged Speed Knots
Maximum Time Submerged and Cruising Range vs. Submerged Speed Knots

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  1. Ordinarily, when operating in areas where a submarine must remain undetected, it is necessary to submerge at the beginning of morning twilight and stay submerged until the end of evening twilight. The distance that can be covered at night depends then, on the time and amount of power available, less that necessary to recharge batteries and air banks. The extreme submerged cruising time of a submarine is in the neighborhood of 36 hours and then at speeds of only 11/2 to 2 knots. This time reduces rapidly with increased submerged speeds. The ability to stay submerged for more than the normal daylight period calls for rigid economy of the auxiliary load being taken from the battery. Figure (1) gives an approximation of the submerged performance of a late type submarine. Performance over and above the submerged period of 20 to 24 hours varies considerably, depending mostly on the necessity for auxiliary power. Figure (2) is based on similarity of all storage batteries when expressed in percent of the one hour rate. Knowing the one-hour submerged speed of a submarine, a fairly good approximation can be made of its capabilities in this respect by reference to figure (2). The war time submerged radius is increased by raising the specific gravity of the electrolyte. Increased specific gravity tends to decrease the life of battery and is therefore not resorted to in peace times. Submarines subsequent to No. 162 are fitted with charging engines and have normal surface speed available while maintaining batteries fully charged. Older submarines must recharge batteries and carry the auxiliary load at the expense of available surface speed.

  2. Submarines have extremely low reserve buoyancy. The unintentional loss of any of this reserve constitutes a serious situation. Designed to stand pressures at depths from 200 to 450 feet, the hull of a submarine is necessarily strong. They must, however, be considered as tender vessels, both bow and stern, due to torpedo tubes and diving planes. For their tonnage, submarines have fairly large drafts and, while there is little superstructure, a submarine will almost invariably back into the wind. Since all submarines are twin screw vessels and fairly well powered for their size, they are not unduly difficult to handle. To those unacquainted with the type, they appear much smaller than they actually are.

  3. Submarines may be expected to submerge in less than 60 seconds.

  4. Tactical diameters vary from 268 to 615 yards with full rudder. The tactical diameters are considerably increased submerged. Turning is very slow submerged, requiring from 70 to 202 seconds, with an average of about 110 seconds to make a 90 degree turn.

  5. Properly handled, a submarine can live through any storm and can be forced into a sea much too heavy for most surface types. The most prevalent danger in forcing a submarine into a heavy sea, is damage to the bow torpedo tubes and bow and stern diving planes, particularly the bow planes if rigged out preparatory to diving. Danger also exists of taking water down main air induction valves and conning tower hatch particularly with the sea abaft the beam. Due to smaller above water line resistance, speed reduction, when heading into the sea, is slightly less than that for surface vessels of same tonnage and speed. Performance of torpedoes fired from submarines in heavy seas or long swells may be expected to be erratic.

  6. (a) A submarine's primary weapon is the torpedo and under some circumstances the torpedo tube mine.

    (b) The deck gun and machine guns are secondary offensive weapons used against lightly armed or unarmed surface craft. The deck gun is available for use against shore objectives when feasible. Guns now fitted on submarines vary from 3" to 6" with maximum effective gun ranges of 5,000 to 10,000 yards, respectively.

    (c) Utmost caution must be used in resorting to a gunfight with any enemy. Submarines are vulnerable to gunfire while on the surface. An enemy attacking by gunfire should be evaded by use of high speed and evasive maneuvers on the surface if practicable. When enemy gunfire appears accurate, submergence is the best form of defense against such attack. When submerged, a submarine can be attacked only with depth charges, torpedoes, mines, various forms of the "mouse-trap" or by ramming. Flat-nose projectiles are generally ineffective. All these forms of explosives must be placed close, to cause

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Image of Figure 2: Submerged Speed Percent of One Hour Rate
Figure 2
Submerged Speed Percent of One Hour Rate

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    material damage, but may have adverse psychological effect on the crew even when no material damage is done. The destruction of any part of the watertight integrity of the pressure hull will usually put the submarine out of commission.

    (d) When a submarine is damaged and unable to dive, the use of high speed and evasive maneuvers together with the available armament are the defensive measures to be taken.

  1. Torpedoes in use have maximum speeds of 29 to 46 knots with ranges of 3,500 to 6,000 yards. The 46 knot torpedo has a range of 9,000 yards at a reduced speed of 31.5 knots. The longer range, slower speed settings of submarine torpedoes are very unlikely to be used except at anchored targets under circumstances which would preclude the submarine's approach to closer ranges; and at large formations, under rare circumstances, when the range cannot be closed.

  2. Torpedo tubes are installed in four different arrangements, and the number of torpedoes carried outside the pressure hull in superstructure stowage tubes are not available for immediate use, as they can be struck below only at night in calm water on account of the danger involved in such an operation during daylight. The following table has been condensed from the pamphlet giving detailed characteristics data of submarines.

    Torpedoes Carried
      Type Arrangement
    of Tubes
    Inside
    Racks and Tubes
    Super-
    structure
    Stowage
    Tubes
    Super-
    structure
    Torpedo
    Tubes
    (a) O-class (Nos. 63-65, 67-71). 4 bow, 0 stern   8     0        
      R-class (Nos. 78-84, 86-97). 4 bow, 0 stern   8     0        
      (Holland) S-class (Nos. 123, 125-146, 153-158). 4 bow, 0 stern   12     0        
      Government S-class (No. 159). 4 bow, 1 stern   14     0        
      Government S-class (116-118). 4 bow, 1 stern   14     0        
      No. 105 and Government S-class (No. 119-122). 4 bow, 0 stern   12     0        
    (b) Mackerel, Marlin Nos. 204-205 4 bow 2 stern   12     0        
      Cachalot and Cuttlefish and Porpoise to Pompano (Nos. 170-181). 4 bow, 2 stern   16     0     *2  
      Dolphin (No. 169). 4 bow, 2 stern   16     3        
      Narwhal and Nautilus (Nos. 167-168) 4 bow, 2 stern   24     10     4  
    (c) Salmon to Seawolf (Nos. 182-197). 4 bow, 4 stern   20     4        
    (d) Tambor to __________ (Nos. 198-203, 206 to _____). 6 bow, 4 stern   24     0        
    * Porpoise, Pike, Tarpon, Permit only.

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  1. When at sea, torpedoes in the tubes are habitually kept fully ready for war shots, except for flooding tubes. At least one complete replacement set is kept ready for reload in the racks. As soon as conditions permit, torpedoes in tubes, which have been flooded, are withdrawn and inspected, after which they are again sealed in the tubes. After firing torpedoes, a submarine can reload in from 5 to 10 minutes. When all torpedoes and mines have been exhausted, a submarine may be expected to withdraw and proceed to its base unless otherwise directed.

  2. (a) Torpedoes are normally fired using periscope for sighting, or on sound bearings, and may be fired on a generated bearing by all modern submarines equipped with the torpedo data computer. The afterbodies of Mark 14 and 15 torpedoes and modifications thereof, are tested to 135 lbs. per square inch. It is safe to fire these torpedoes at a depth of 180 feet measured to the keel with a tube pressure of 135 lbs. per square inch. This gives an effective ejection pressure of 40 lbs. per square inch. In S-class submarines, when firing below periscope depth, to insure necessary ejection velocity of the torpedo, two impulse tanks must be cross connected. It is believed that our present torpedoes will perform satisfactorily when subjected to pressures slightly in excess of the test pressure. However, it is recommended that these test pressures be not exceeded unless it is absolutely necessary to do so. When firing below periscope depth, be especially mindful of the possibility of flooding the torpedo afterbody if the tube outer door is left in the open position for too long a period of time.

    (b) The Bureau of Ordnance states that torpedoes should not be fired at depths greater than 120 feet by any submarine. This is a matter of peace-time practice, however, in actual war operations if the commanding officer of a submarine finds himself below 120 feet and deems it advisable to launch torpedoes, it is his prerogative to do so. When required to fire torpedoes at a depth below 120 feet, the poppet valves should be made inoperative.

  3. Habitability on the surface is fair under good conditions and poor in heavy seas. Habitability is generally poor under all conditions of extensive submerged operations, and prolonged dives in tropical waters are extremely enervating. Submarines are equipped with air-conditioning apparatus which greatly improves habitability. Oil fumes and battery gases cannot be disposed of, when submerged. For long dives, the air is purified by use of a CO2 absorbent and the addition of pure oxygen to the air. Ordinarily, a submarine may remain submerged about 15 hours without air purification.

  4. Visual communications, and radio and sound communications submerged, have limitations which must be recognized in the successful employment of submarines. For peace-time surface cruising, searchlight, semaphore, and blinker are used effectively within the limits of their range of visibility. Receipt for flag hoists is impracticable except when accomplished by searchlight. Signalling either by semaphore or searchlight is undesirable whenever the necessity of diving is imminent. Submarines are equipped with either housing vertical antennas or makeshift periscope antennas for use submerged. Reliable two way communication up to 50 miles, on frequencies above 2000 kcs. may be expected with the latter, while with the modern equipment, in submarines subsequent to No. 171, this range may be extended to 100 miles. Exposure of vertical antennas is subject to the same restrictions applicable to proper periscope handling, but its use is more limited because a greater length must be continuously exposed for a considerable period of time in order to transmit or receive messages. Underwater reception of low frequency signals from a high power shore station is possible in submarines equipped with permanent direction-finder loops. Good reception is possible at distances of 2,000 to 3,000 miles with the loop submerged not more than 15 to 20 feet. When submarines are patrolling submerged during daylight, information and directives will be disseminated by "F" method on regular schedules, circumstances permitting. All such communications will be retransmitted at night after all units have surfaced in order to insure delivery. Submarines subsequent to Number 165 are fitted with echo-ranging equipment which enables them under some circumstances to communicate, when submerged, with each other and with friendly surface

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    craft. Their use, and the use of fathometers, should be avoided when it will facilitate detection by enemy patrols. All submarines, subsequent to Number 165, have keel-mounted supersonic equipment available for use when on the surface for detecting the presence of other vessels during darkness or low visibility.

  1. A basic advantage exists in the use of small submarines in operations against enemy submarines. If surface craft, and even aircraft, are used exclusively for this purpose, the enemy submarine can remain on the surface for at least a portion of the time. On the other hand, if there is any possibility of own submarines being in the vicinity, the enemy submarine will have to remain submerged throughout daylight hours or risk the possibility of submarine attacks. This has the effect of forcing him to do all battery charging at night or in thick weather, and in addition reduces his effective speed of advance and reduces efficiency and morale of his crew. For this same reason, the mere presence of own submarines ahead of own fleet will serve to reduce effectiveness of enemy submarines, in maintaining striking position ahead of their own fleet.

  2. The history of submarine warfare indicates that even the occasional appearance of submarines in widely separated areas, serves a useful purpose in requiring the enemy to take defensive measures out of all proportion to the effort required to produce them. Establishment of convoy systems, with resultant reduction in the service of supply, and the extended dispersion and augmentation of anti-submarine units and measures, follow. This stratagem also serves to restrict and complicate the freedom of movement of the enemy's men of war.

  3. For those interested in counter measures against submarine warfare, the question of lookouts is of importance. Experience with surface vessels and aircraft engaged in target services to submarines during torpedo practices indicates that the pilot, observer or quartermaster who has had considerable experience looking for periscopes and knows what to look for, will invariably pick one up without false alarms long before the average lookout, not so trained and experienced. In the training and assignment of lookouts, the fact must be borne in mind that the proficient submarine approach officer strives to complete his observations within a few seconds for each exposure. Under these conditions, confirmation of a lookout's report by the officer of the deck or officer in charge of lookouts, is impracticable. The lookout must know what to look for and must be sufficiently alert and reliable that his reports do not need confirmation if false alarms with resultant confusion are to be avoided.

  4. Echo-ranging apparatus used as a listening device, is an excellent detector of torpedoes after they have been fired. Torpedoes make a distinctive sound and trained operators can track them with fair accuracy. This feature is especially valuable in detecting wakeless torpedoes.

  5. If one of our own planes sights an enemy submarine, the surest way to make him submerge is to attack. If, for any reason, it is desired to have enemy submarines remain on the surface rather than submerged, or if it is desirable to keep them from giving the alarm to other submarines on the surface in the vicinity, plane observation, when not accompanied by attack, should be made from maximum range.

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Section 2
Doctrine for the Operations of the Individual Submarine

  1. The primary objectives of submarines are enemy ships.

  2. The primary weapon of the submarine is the torpedo; the secondary weapons are the mine and gun.

  3. The ability of the submarine to deliver an attack successfully depends on remaining unseen and unheard until the attack is completed.

  4. Having started an attack, deliver it as soon as a satisfactory firing position is reached. Waiting for an improved firing position almost invariably jeopardizes the satisfactory position already attained and increases chances of detection.

  5. Attacks should be carried to as close a range as possible to insure hitting, keeping in mind arming distance of torpedo exploders.

  6. The number of torpedoes fired should be sufficient to insure destruction or crippling of the enemy. (see paragraph 4614).

  7. On attacks at short range a torpedo spread should be used to cover at least 80% of the target length.

  8. Should a submarine be unable to reach a close firing position, the torpedoes should be spread so that the target cannot avoid all of them. This principle also applies to sound attacks.

  9. In using multiple-speed torpedoes, the highest power setting that will insure the torpedoes reaching the target, should be used.

  10. Empty tubes should be reloaded immediately if the noise made in reloading is unlikely to draw immediate counter attacks.

  11. With radar operating, a submarine on the surface can usually detect enemy aircraft in sufficient time to dive to a safe depth. In clear water, in vicinity of the enemy, a submerged submarine must be particularly careful of periscope exposures, and running too shallow between periscope exposures.

  12. (a) The basic defense of the submarine against aircraft lies in quick and deep submergence followed by evading action.

    (b) Against surface craft, quick submergence plus information gained of enemy action from periscope observations and sound are basic for evasion if the contact is at close range. Silent running should be employed.

    (c) At night, and in some conditions of low visibility when the contact is not at close range, evasion may be accomplished most successfully by use of high surface speed and evasive tactics.

  13. With alert personnel and radars in operation submarines on the surface in reduced visibility are not subject to surprise attack.

  14. Submarines are in diving trim and ready to dive immediately at all times when at sea.

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  1. Periscopes and periscope antennas should be exposed only at relatively slow speeds. After reducing speed, sufficient time should be allowed to permit the vessel to lose headway. This is one of the most important points in connection with the prevention of detection.

  2. The handling of the submarine by section watches, during surface and submerged operations, is standard practice.

  3. Vessels should take every opportunity to run "silent" at slow speeds. Development of sound apparatus will make such silent operations more and more essential in war.

  4. Batteries and air banks should be kept as fully charged as operations will allow.

  5. The necessity for efficient lookouts cannot be over-emphasized.

  6. In rough weather, diving is facilitated by having the seam on the beam or slightly abaft the beam.

  7. Before coming to periscope depth after running deep:

    1. Thoroughly listen through 360° for external sounds.

    2. Bring the submarine up smartly to periscope depth and quickly observer through 360°l; in low power.

    3. If all is clear, follow this by a slower and more careful 360° search in high power.

    In coming to periscope depth, control should be such as to permit immediate return to deep submergence.

  8. While cruising on the surface in daylight, the highest periscope should be manned, as an additional lookout station.

  9. Close at high speed to insure getting good firing position; at the same time, bear in mind possibility of sight and sound detection.

  10. If possible, choose the firing side according to sun and weather conditions, but do not delay getting in on this account.

  11. If water is clear and air screen is present or suspected, go deep between periscope exposures to avoid aircraft detection. This precaution is particularly important for vessels painted with the light camouflage paint. When the surface is choppy or in certain unclear northern waters this is probably unnecessary.

  12. Time between exposures depends on visibility, speed of enemy, and expected air and screen surface ship menace. Learn to rely on sound gear and reduce number of exposures.

  13. Get tubes ready for firing in plenty of time to avoid a last minute delay, but keep in mind the possibility of flooding torpedo afterbody.

  14. Always parallel periscope data with sound data. It may be necessary to go deep for firing. Keep proper setup on angle solver for use in case of failure of T.D.C.

  15. Firing bubbles must be avoided by efficient use of poppet valves. Too much, rather than too little, water should be allowed to enter the submarine.

  16. Regarding the safe depth at which to fire torpedoes, see paragraph 1134.

  17. Attention is directed to the following pertinent articles of F.T.P. 183, 188, and 143, which concern the employment of submarines:

    F.T.P. 143, Articles 414(f), 825(b), 10142-10146, 1231-1233, 12129-12137, 12150-12154, 12209-12212, 12253, 12268, 12283, 12306, 12321, and 1254.

    F.T.P. 183, Article 133.

    F.T.P. 188, Chapter VI, Articles 1112, 1141, 1313, and the parts of the following applicable to submarine employment: Chapter VIII, Chapter IX, pages 9-1 to 9-27, Articles 1154-1159, 1323-1330, Chapter XIV and Chapter XV.

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