War Instructions United States Navy 1944

Chapter 7. Action Against Submarines, Aircraft, Mines, Chemicals

Section I. Antisubmarine Measures

General Action

700. The normal measures surface craft take against submarines are:

  1. Evasive action to prevent submarines from gaining favorable attack positions and to reduce their accuracy of torpedo fire.

  2. Measures designed to detect submarines.

  3. Offensive action against submarines after contact is made.

Evasive Action

701. When practicable, known submarine waters are avoided. Also effort is made to avoid passing through, or in close proximity to the same waters traversed in the preceding twenty-four hours.

702. When cruising, the officer in tactical command normally orders his command to zigzag in accordance with a prescribed plan, whenever there is a probability of encountering enemy submarines. Various types of zigzag plans are promulgated but the commander is not restricted thereby from preparing his own plan if he so desires. In the preparation and selection of zigzag plans consideration is given to the size and type of the formation and disposition, the availability of vessels for the antisubmarine screen, the speed that can be maintained, the time and fuel available, whether or not submarines are definitely known to be in the area and the maneuvering characteristics of the ships, particularly non-combatant ships.

703. Generally speaking, all vessels, even though adequately screened, zigzag in submarine waters.

704. During thick weather and at night, except on very clear nights or during bright moonlight, vessels normally cease zigzagging.

705. When zigzagging, ships in the various formations are disposed on lines of bearing other than the base course.

706. Special circumstances, including the presence of enemy vessels, may require a departure from the above instructions regarding zigzagging. Large, slow-speed formations benefit little from zigzagging, as some ship of the formation is always near the mean track and the reduced distance made good affords the submarine additional opportunity to attack. Where the speed of the ships comprising the disposition is less than twelve knots, evasive steering may be reported to. In this case radical changes of course are made at irregular intervals of not less than 1 hour.

707. Single ships of any speed zigzag in dangerous submarine waters. Low-speed ships use very little rudder and a zigzag plan with short legs. The primary purpose is to reduce the accuracy of torpedo fire, rather than to evade the submarine, since evasion is not feasible.

708. In special circumstances, where excessive danger of submarine attack exists, frequent speed changes may be made while zigzagging, and provision may be made for the use of different speeds while on different legs of the zigzag plan. By running their shafts at different speeds, individual ships may confuse submarines endeavoring to estimate speed by a propeller count. The difference in shaft speeds should vary by as much as three knots.


709. Submarines trailing or lying in wait in anticipation of making a night surface attack may be evaded by a radical course change made soon after dark. Trailing vessels and shadowing aircraft are destroyed or driven off whenever they are detected.

Detection of Submarines

710. Search for submarines is carried out with all possible means. These include:
  1. Efficient lookouts.
  2. Sonar.
  3. Radar.
  4. Radio direction finder.
  5. Aircraft.

711. When in submarine waters, both day and night, all ships equipped with sonar gear maintain continuous watch in accordance with current fleet instructions. Radar watches are maintained as prescribed by the officer in tactical command.

Action After Sighting Submarine

712. Danger from enemy submarines is best met by offensive action on the part of aircraft and antisubmarine vessels, combined with evasion where location of submarines is known.

713. Aircraft of the antisubmarine patrol and ships of the screen sighting a submarine, attack immediately, conforming to current fleet tactical instructions in prosecuting the attack, hunt and kill.

714. Vessels whose mission or characteristics are to take offensive action against submarines may maneuver to avoid torpedoes, but they vigorously drive home the attack on threatening submarines.

715. Vessels acting singly, or vessels in company but so disposed that radical maneuvers by a vessel will not interfere with other vessels, maneuver as prescribed in fleet tactical publications when a submarine is sighted. Individual ships must be prepared to maneuver radically to avoid torpedoes.

716. When vessels are in company, radical independent maneuvers and changes in speed may cause confusion resulting in the hazard of collision becoming greater than the hazard of submarine attack. In this case, therefore, maneuvers to avoid submarine attack are as directed by the officer in tactical command or evolution unit commander. However, the restrictions on individual action by ships in formation are not construed to prevent maneuvers to avoid torpedoes, when these obviously would not involve serious risk of collision with other vessels in the formation.

717. A force screened maneuvers clear of the area of the hunt, using increased speed as necessary and practicable, but any ships of this force drop depth charges if in a favorable position to do so.

Section II. Antiaircraft Measures


718. Search radars are the best means of detecting approaching aircraft, but they are not fool proof. They may be jammed. Operation may be poor. However, even when such equipment is operating free from interference, a vigilant lookout is maintained.

719. Each ship organizes a well coordinated aircraft lookout system which covers all sectors. Full use is made of optical instruments to aid vision, and special measures are provided for searching near the sun. Aircraft lookout watches are not over one-half hour's duration, if practicable.

720. As air attacks may occur at any time, all ships must be prepared to repel such attacks, regardless of formation or disposition.


721. The time available to repel an air attack is generally so short, and quick action is so essential, that it is vital to keep an adequate proportion of the armament manned and the personnel fully alert when in an area where air attack is possible or when it is imminent.

722. During daylight hours a proportion of close=-range antiaircraft weapons are always kept on the bearing of greatest danger (i.e., toward the sun or toward low clouds), as attack is most likely to take place from such direction.

723. During twilight and on moonlit nights the more dangerous side is that opposite to the light or moon, and the major portion of the close-range antiaircraft armament is, if practicable, kept bearing in that direction.

724. Commanding officers are indoctrinated with the necessity for prompt action during air attacks, when signals normally are emergency signals and therefore executed as soon as understood. They are guided by current fleet doctrine in regard to what discretion is permitted them in opening fire or maneuvering independently, but are expected to act energetically within these limitations.

725. In general, an individual ship, a division commander, or a unit commander, increases speed and maneuvers radically to avoid torpedo attack or bombing attack, having due regard for the existing situation and the danger of collision. Likewise, individual ships maneuver to bring the greatest volume of antiaircraft gunfire to bear on enemy planes for short periods; having due regard for maintaining approximate positions in the formation, and remaining so disposed as to be able to support and be supported by the formation.

726. Each ship, within the capabilities of its type, establishes and maintains communications with air cover (Army or Navy) and exercises fighter direction for fighter interception control in accordance with current fleet doctrine.

727. Ships equipped with degaussing coils keep coils energized with appropriate settings at all times when there is danger of being mined or torpedoed.

Warning of Attack

728. Warning of approaching aircraft may be obtained from information received by radio or signals, radar, air patrols, pickets, and sky or surface lookouts of surface ships.

729. During an air attack it is of primary importance that provision be made for continuous, all-around radar search; otherwise, an attack by new hostile aircraft may develop undetected.

730. The presence of shadowing aircraft may indicate that an attack is imminent.

731. Screening vessels sighting approaching unidentified aircraft give warning of their presence by prescribed means, and if enemy or their attitude of maneuver indicates hostile character, take them under fire when they are within range.

Evasive Measures

732. The chance of evading air attack is increased by:

  1. Using routes which pass outside ordinary air search radius from enemy air bases, and avoiding passing through, or in close proximity to the same waters traversed in the preceding twenty-four hours.

  2. Keeping out of sight of land from which enemy observations may be made.

  3. Making landfalls during darkness or periods of low visibility.

  4. Changing course immediately after dark, if detected, so as to cause a large displacement from the mean line of advance.

  5. Destroying trailing or shadowing enemy forces.

  6. Using, as opportunity offers, weather fronts, isolated rain squalls, or patches of low visibility.


  1. Choosing courses into the light horizon at dawn, sunset, moonrise, and moonset, whenever practicable. Such procedure both reduces the chance of discovery and increases the length of time an enemy attacking "up-light" will be exposed to counter-attack.

  2. Reducing speed, if circumstances warrant, as a means of eliminating wake.

  3. Laying smoke screen, if spotted, and if the situation permits.

Use of Gunfire

733. Any gunfire is effective in reducing the accuracy of bombing, even when the chance of hitting the planes is small. Even weak, poorly armed ships may reduce their chances of being hit by maintaining a well disciplined fire whenever the planes are within effective range. Experience has shown that attacks may be pressed home less closely in the face of heavy antiaircraft fire. Such fire usually causes the planes to drop their bombs or torpedoes at greater altitudes or ranges with less chance of success.

734. The general tendency, particularly with small caliber guns, is to open fire too soon, thus wasting ammunition and reducing the volume of fire which can be maintained later while the planes are within effective range.

735. The antiaircraft control organization must be sufficiently flexible to permit any weapon to open fire in the case of surprise attack at the discretion of the senior officer or petty officer at the weapon. To this end, all antiaircraft personnel must be proficient in recognizing own and enemy aircraft.

736. Control of gunfire against attacking planes is in accordance with the ship's type and the current fleet doctrine.

Use of Maneuver

737. The manner of maneuver which experience indicates to be most effective against various types of air attack is delineated in current tactical publications. Maneuvering tactics may be expected to change with the advent of new types and methods of attack. However, during an air attack a vessel must be ready for high speed and radical change of course.

Use of Fighter Protection

738. The fighter director at all times controls the available fighter cover. When warning of approaching aircraft is received, the fighter director directs the fighter protection to prevent impending air attack. The fighters intercept the enemy at a position allowing them to carry out successive attacks before the enemy reaches the maximum range of our long-range antiaircraft weapons. Our fighters discontinue the attack when our antiaircraft fire becomes too dangerous.

739. The primary defense during daylight against an air attack is fighter interception. The accomplishment of this depends upon good radar detection in addition to good communications.

740. Fighter protection destroys trailing or shadowing enemy aircraft.

Defense Against Night Air Attack

741. At night primary reliance is on antiaircraft fire power and maneuvers rather than on fighter protection. Night fighters are used when available. As the number that can be effectively controlled at one time is small, they are best employed against trailing enemy planes. They are also used effectively in disrupting large scale attacks. Generally ships use gunfire and maneuver as during a day attack, except that a smoke screen aids in concealing wakes.

742. During night action it is to be expected that guns not using flashless powder will blind personnel of other batteries.

743. At night when unidentified aircraft are detected, the officer in tactical command, before opening gunfire, weighs the possibility of destroying enemy aircraft against the likelihood of disclosing the formation position.


Section III. Mines

General Information

744. Intelligent action to avoid damage by mines is based upon knowledge of the characteristics of the mines the enemy is most likely to employ. These characteristics are capable of considerable variation. New types of mines are constantly being developed to take advantage of particular situations, and operational practices of the opponent. In conjunction therewith, knowledge of the characteristics of our own mines as set forth in appropriate publications is essential.

745. Safety from mines depends upon knowledge of the area the enemy has mined, thorough sweeping, and the employment of protective measures by individual ships.

746. Ground mines may be anticipated in depths of less than 30 fathoms. Moored mines may be anticipated in waters of any depth up to 500 fathoms although they have usually been laid in depths of less than 200 fathoms. Large defensive minefields usually consist of moored mines, either contact or controlled.


747. Ships always use swept channels or swept areas when possible.

748. When operating in waters where enemy mines may be encountered, paravanes are used by ships so fitted when ordered by the officer in tactical command. Ships having protective devices against influence mines make them operative without orders.

749. When proceeding through mineable waters, suitably equipped minesweepers or other ships capable of maintaining the required speed are, if available, used for sweeping ahead of the large ships of a force.

750. Enemy minefields that cannot be avoided have a safe channel swept through them when military considerations permit.

751. Channels which are designated for the passage of shipping are swept as frequently as deemed necessary, and in consideration of the facilities available.

752. When it becomes necessary to cross an area in which moored mines are planted, particularly if it has not been possible to sweep the area, a column formation, with the leading ships streaming paravanes, is taken. If an explosion occurs under a ship in a column formation, following ships pass as close as possible to the point where the explosion took place, rather than giving this location a wide berth. If the tidal range is large or the currents are strong, it may be possible to select a time for passage when the mines will necessarily be so far below the surface that the ship will be safe. However, some enemy mines are laid with slack mooring lines so that the mine, or a float attached to the mine, is continuously watching.

753. All floating objects whose character is in any degree uncertain are carefully avoided. Mines may be secured to the bottom of dummy periscopes, concealed in waterlogged boats, or attached to wreckage of various kinds.

754. The possibility of the enemy using ships which are apparently neutral for the purpose of laying mines is given due consideration.

755. The use of sabotage mines occurs from time to time, particularly in neutral ports. Appropriate precautions are necessary.

Action Upon Sighting

756. Any ship in the vicinity of a force sighting a mine or mines in the path of the force or other ships, immediately makes the appropriate emergency mine warning signal. Aircraft sighting mines under similar circumstances immediately report the fact and, in addition, indicate the position of the mines by prescribed or appropriate measures or maneuvers.


757. Any ship or aircraft encountering mines well ahead of a force, or in any other area through which our forces might pass, reports the type of mines sighted, their position, and also the action taken.

758. If practicable, the position of a mine is indicated by a ship or aircraft, preferably a screening ship or other small vessel, remaining in the vicinity of the mine, until all of our units menaced by the mine are clear. When practicable, the mine is destroyed.

759. If mines are encountered in the path of a force, or other ships, the officer in tactical command, or the senior officer of the ships menaced by the mines, takes immediate and appropriate action to avoid the mines.

Section IV. Chemical Defense

760. Chemical defense afloat is based on the following concepts of chemical warfare:

  1. Chemical attack against naval vessels is possible but not highly probable except at anchor in restricted waters or during and after a landing in amphibious operations. At these times our forces are particularly vulnerable.

  2. Chemical attacks on naval vessels are to be expected in the form of:

    1. Aircraft spray consisting of blister gases and tear gases delivered by aircraft to cripple a ship's personnel. This form of attack is accurately made only at low altitudes and is most probable when a force is cruising in low visibility, particularly at dawn or dusk, during landing operations, or while at anchor.

    2. Chemical shells containing tear gas, which is the only known chemical warfare agent adaptable for effective use in armor-piercing projectiles, as all other agents are rendered harmless by the explosion of the filler. Other agents are possible to be used, particularly against landing operations, in all types of artillery, mortar, and rocket shells. These contain a large charge of chemical but have no high explosive effect. On account of its inability to effect material damage, this type of shell is not expected to be used in naval engagement.

    3. Chemical bombs which contain any of the chemical warfare agents and are especially useful in creating a heavy concentration at a particular point. This is in contrast to spray which produces a more or less uniform contamination over an entire area.

761. Protection of personnel against chemical attack is for the purpose of promoting the offensive power of a ship. A probability that chemicals may be encountered does not justify resort to individual protection, particularly gas masks, at the expense of efficiency in the performance of battle duties. When chemicals are actually present during battle, individual protection which is any manner constitutes an interference with ones duty, is used only when such protection results in an increase in efficiency. General protection is obtained in some degree by the setting of the highest material condition.

762. Commanders afloat use the general and individual protection provided in accordance with the above policies, and the detailed instructions appearing in pertinent publications.


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