War Instructions United States Navy 1944

Chapter 9. Employment of Submarines

Section I. Submarine Characteristics

900. The modern submarine is a seaworthy, rugged craft. On the surface it has long cruising radius, a maximum speed of 17-21 knots, guns for use against surface craft and aircraft, radio capable of long range transmission, and radar. Its maximum speed awash is about 14 knots. Submerged it has a low speed (2-knot) cruising radius of about 90 miles and a submerged endurance of about 45 hours lying on the bottom. Its maximum submerged speed is normally 8-9 knots, but usually with full battery charge this speed can be maintained for only about one hour. Although under certain conditions it can receive radio messages while submerged, this method cannot be relied upon as an effective means of communication.

901. Habitability on the surface and submerged is generally fair under all conditions of extensive operations, if submarines are equipped with air-conditioning apparatus. Although this equipment greatly improves the ship's habitability, oil fumes and battery gases cannot be disposed of when submerged.

902. The principal weapon of the submarine is the torpedo of 30-45 knots speed, with ranges of about 9,000-4,500 yards respectively. Both air-driven and electrical-driven torpedoes are used, the latter showing no wake. Chemically driven torpedoes, which are wakeless, may be developed.

903. All submarines can plant specially constructed mines through their torpedo tubes.

Section II. Submarine Tactics

904. In making a torpedo attack submarines may use radar, observe their tarket by short (about 10 seconds) exposures of the periscope, or keep track of its bearing and range by supersonic devices. In the latter case the attack can be made without recourse to the periscope from depths as great as 120 feet.

905. Group attacks are sometimes made in the form of a series of attacks, each submarine launching an attack when in a favorable position.

906. Submarines unsupported, or acting in conjunction with air reconnaissance, can deliver night surface attacks. To attain position for such attacks they may lie in wait in the path of the enemy, or may trail during daylight and proceed to an advanced position during the early dark hours.

907. When conditions permit and the choice is open to the submarine, its attack will be made:

With wind and sea astern.
From the direction of the sun.
From the side away from the moon.
With the target silhouetted against rising or setting sun.
From the side least protected by screening ships.
In reduced or spotty visibility from the dark side.

908. The most favorable position for firing with respect to bearing is from 70° to 110° relative to the target's course. However, the low submerged speed of the submarine limits its commander severely in the choice of approach bearings.

909. The ability of a submarine to submerge enables it to deliver surprise torpedo attacks at close range, to lay mines in waters controlled by or under observation of the enemy, and to obtain

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information of the enemy under conditions which preclude scouting by other types. The small silhouette of an awash submarine is very difficult to see at night, and affords the submarine an advantage for night surface attacks.

910. The most serious limitations of the submarine are its vulnerability and medium speed on the surface and its short radius of action and slow speed submerged. The latter factors are coupled with the necessity of recharging batteries on the surface when the limits of submerged endurance have been reached.

911. Secrecy and surprise constitute the essence of successful submarine warfare. Any projected submarine operations which do not provide these elements, which do not contemplate utilizing the advantages accruing from the ability to submerge, and which fail to take into account the inherent limitations of the type, constitute a sacrifice of the potential military value of this weapon.

Section III. Doctrine of General Employment

912. Submarines are normally employed to attack with torpedoes those enemy units whose destruction or damage would most seriously interfere with the successful prosecution of enemy operations. Given a choice of favorable targets, submarines ordinarily are required to attack heavy combatant ships or loaded transports in preference to light craft or auxiliaries. However, they are thoroughly indoctrinated to seize every opportunity for a successful attack on suitable enemy ships, and not to forego such opportunities in the hope of encountering a more important target.

913. On occasion the mission of the submarine may be such that the successful accomplishment of its task would be jeopardized by indiscriminate attacks. On such occasion the orders to the submarines must clearly state the circumstances under which they are to refrain from attacking.

914. Submarines are also employed for scouting, screening, attacks on enemy lines of communications, mining, and services to aircraft, including rescue of personnel. Other tasks may include delivery of supplies to blockaded ports, delivery of important communications, cable cutting the landing and recovery of spies and demolition or raiding parties in enemy territory, and acting as beacons to guide attack forces to beaches, channels, or bombardment areas.

915. 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 submarine effort. The establishment of convoy systems and the adoption of circuitous shipping routes with their consequential reduction in the service of supply, the diversion of combatant forces to the defense of shipping, the dispersion of forces and the restrictions imposed on the free movements of combatant forces to the defense of shipping, the dispersion of forces and the restrictions imposed on the free movements of combatant units, are all forced upon the enemy by the skillful and judicious use of even a few submarines.

Scouting

916. Submarines are generally unsuited for tactical scouting due to their medium surface speed, the ease with which they can be forced to submerge, and the short distance to their visible horizon. They are, however, particularly suitable for conducting unsupported observation in waters under enemy control. When such waters are patrolled by enemy submarines or aircraft, the submarine scout is usually compelled to remain submerged during daylight to conceal his position and guard against surprise attack. It is also usually necessary for him to observe radio silence except for vital contact reports; otherwise he may be located promptly by radio direction finders, his safety jeopardized, and his usefulness greatly curtailed. However, under certain conditions submarines can receive radio messages while at periscope depth, or deeper if the power is sufficient, but this method cannot be wholly relied upon for effective communication. Transmission, when necessary, may be accomplished at night, accepting in such event possibility of enemy detection by radio direction finder.

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Screening

917. Submarines may be utilized for screening operations and are best employed as a distant screen across an enemy line of advance to inform own forces of any enemy attempting to intercept. However, enemy air activity will seriously reduce the effectiveness of this type of screen.

Operations Against Enemy Lines of Communication

918. Attacks on military lines of communication and the destruction of sea-borne commerce usually partake of the nature of patrol, individual submarines being assigned to well defined areas. As a countermeasure against this form of submarine warfare, the enemy will probably employ the convoy system, using surface and air escorts which will undoubtedly be reinforced near focal and terminal points. On the high seas enemy shipping, including convoys, will probably be given a circuitous routing.

919. In operations of this nature the concentration of submarine activities in the vicinity of focal and terminal points results in greater damage to the enemy, although the submarines themselves are subjected to intensified antisubmarine measures. Their positions are frequently shifted to cover variations in shipping routes and to evade enemy counter-action.

920. Submarines operating in enemy waters are not required to transmit reports by radio, except on special occasions where the importance of the communication to be transmitted justifies the disclosure of its position, or on occasions when it is desired to attempt to harass or mislead the enemy by transmissions.

Mining

921. Submarines lay mines in waters under enemy control where surface mine layers would be subjected to attack or detection. Submarines despatched on such missions attack with torpedoes any favorable targets encountered, unless otherwise directed.

Services to Aircraft

922. Some submarines are capable of carrying gasoline, lubricating oil, and minor supplies for aircraft. Planes can be fueled underway in the open sea under favorable conditions as well as in protected roadsteads. A squadron of patrol planes can be serviced rapidly and efficiently. Thus, submarines may be used to support seaplane flights to and from outlying points where surface tenders are not available or cannot be maintained. Submarines may also be used for personnel rescue during air operations.

Employment of Submarines in Antisubmarine Warfare

923. A basic advantage exists in the use of own 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 at least a portion of the time. On the other hand, if there is any possibility of our submarines being in the vicinity, the enemy submarines will probably remain submerged throughout daylight hours. 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 lowers the efficiency and morale of his crew. For this same reason the mere presence of our submarines ahead of a surface force serves to reduce the effectiveness of enemy submarines in maintaining a striking position ahead of their own force.

Operations of Attrition

924. In opposing an enemy advance, submarines may be employed for observation, reconnoitering and for attrition attacks. Normally this employment requires the stationing of submarines as patrol units near the enemy's known point of departure and along focal points in the

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line of his advance. When the enemy's speed is relatively high or when he has the choice of several divergent routes it is best to concentrate our submarines in the vicinity of his known destination, as otherwise he may be able to avoid the areas in which they are disposed. This is especially true in cases where slow submarines only are available. Operations of attrition may be conducted under circumstances in which the destruction of enemy auxiliaries or transports is temporarily of greater moment than the destruction of his combatant ships.

Section IV. Submarine Operations in Conjunction With Other Types

925. While submarines may operate unsupported in any of the types of operations previously discussed, it is obvious that their effectiveness will often be enhanced if their activities are coordinated with or supported by the activities of other types.

926. A very profitable form of coordinated operations consists of cooperation between aircraft and submarines, the former supplying information upon which the submarines may proceed to positions favorable for attack.

927. In joint submarine and aircraft operations, except when specifically called for in prearranged plans, aircraft normally avoid areas known to be occupied by own submarines, do not approach submarines known to be friendly and avoid maneuvers which could be construed as attacks. Submarines are required to initiate identification procedure on sighting friendly aircraft.

928. Whenever submarines are operating with other forces all ships and aircraft must be informed of the location and probable operations of these submarines. This includes submarine operations ahead of our own forces, on scouting lines, in the enemy's probable track, and off bases or objectives.

929. Aircraft must be kept fully informed of submarine operations when submarines act in conjunction with aircraft. Submarines proceed to and from their stations in definitely specified lanes which they will enter at pre-established times. During at least part of their surface runs, especially when within range of shore defenses they are escorted by surface ships.

930. In the vicinity of our bases an area designated as a submarine sanctuary is established in which submarines will be free from attack during specified periods. When friendly submarines which have been submerged in the vicinity of the base desire to surface they do so within the limits of the sanctuary and identify themselves before proceeding out of it.

931. No positions for submarines are normally prescribed in approach, contact and battle dispositions as, in general, submarines operations are coordinated, but not closely combined with those of surface craft composing such dispositions.

932. In anticipation of a major action, the submarines may be deployed on the surface across or flanking the line of advance of the enemy heavy ships. If possible the deployment is made during darkness or low visibility or under cover of an aircraft screen, so that the disposition of the submarines will not be disclosed to the enemy. It is normally completed in time to permit undetected submergence in positions from which attack can be delivered.

933. Submarines that are initially unfavorably situated for attaining an attack position prior to a major action may be so disposed as to permit them to attack the enemy's heavy ships in case of a reversal of the action, or to sink damaged enemy heavy ships which may withdraw or fall out of his battle line.

934. In cases when it is probable that the enemy will retire to a known base or area, such submarines as have been unable to attack during the major engagement and submarines no longer in position to attack but having torpedoes remaining, may be disposed along the enemy's line of retreat for the purpose of attacking as he retires.

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Section V. Submarines Cruising in Company With or in the Vicinity of Friendly Forces

935. Unless special precautions are carefully observed submarines are in grave danger of being treated as hostile if they come to the surface in the presence of their own forces.

936. Submarines do not pass through own dispositions or formations if it is possible to avoid doing so.

937. If it is necessary for submarines to pass through a disposition or formation they do so on the surface and are escorted by one or more surface vessels. All task subdivisions are informed of the movement.

938. It may be expected that a submarine will never emerge in the presence of friendly surface craft or aircraft, except in an emergency, without first establishing its identity.

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