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American Patrol Detachment - Anti-Submarine Doctrine




JULY 14, 1918


     A doctrine lays down in general terms the correct principles of action and the proper procedure for normal situations. It does not pretend to cover all the possible situations which might arise in actual practice. It should therefore be interpreted liberally; the spirit of the doctrine should be followed as closely as possible so that all vessels will know what course of action they may expect from other vessels of the Detachment and proper co-ordination of effort will be ensured. In unusual situations, however, officers must act promptly on their own initiative in the manner they believe best suited to the occasion. It is far better to attempt something, even though a mistake be made, than to lose one of those precious opportunities which presents themselves so seldom.



1.   During daylight a submarine sighting a vessel will attempt to gain a position ahead of her by running at high speed on the surface, keeping at such a distance from the vessel that her tops are below the horizon. When the vessel’s tops come into view the submarine will submerge, so that it cannot be seen by the lookouts which will presumably be stationed in them. If the submarine, at the time of submergence, is less than three points on the target’s bow, an attack can be made.

(a) If it is possible for the submarine to gain a position directly ahead of the target while still at a considerable distance a stern shot attack will probably be made. The submarine proceeds at slowest possible speed directly at the target on an exactly opposite course. When at close range, it will either turn about 90 degrees to the right or left and fire a direct stern shot at about 200 yards range or will pass the target on an opposite course at a range of from one to three hundred yards and fire a 90 degree angle stern shot while passing.

(b) If the submarine is nearly three points on the target’s bow at the time of submergence, it will run submerged at a high speed on a course at right angles to the bearing of the target, until certain of being able to get in an attack. Then it will change course until it is running at about right angles to that of the target and slow to about 4 knots speed, firing the bow tube when a range of about 250 is reached. If the submarine finds it is getting in too close, it will change to a course parallel to that of the target and fire a 90 degree bow shot.

(c) If it is considered desirable for the attack to be carried through as quickly as possible, the submarine runs at full speed submerged and steers a “collision course”. When a range of 2000 yards is reached the usual slow speed attack is made. During all forms of attack frequent periscope observations are taken, slowest possible speed being used at these times.

2.   A submarine attacking in daylight will probably attack with the wind. When running in this direction the periscope, moving with the wind and sea, will cause little commotion and will be very difficult to see. If the submarine is running against the wind and sea, a great amount of spray will be thrown up and it will be a much easier mark for the lookout. If the submarine makes an attack from the windward position, a bow shot will probably be fired; if from the leeward position a stern shot.

3.   A submarine will attempt to make her approach from the direction of the sun. This form of attack will be especially effective when the sun is near the horizon; then it will be extremely difficult to see the periscope if it is skillfully exposed.

4.   A submarine will rarely make a torpedo attack in a calm sea, as the wake made by the periscope and that of the torpedo can be seen for great distances.

5.   A wind of force 3-4 presents the best chances for the submarine because the numerous whitecaps make it difficult to detect the wake of periscope and torpedo.

6.   If the wind is of force 6-7 it will be difficult for the submarine to fire without exposing the conning tower. Also the torpedo is liable to broach unless its course is parallel to the trough of the seas.

7.   Submarines proceeding on the surface are frequently disguised as sailing vessels or steamers.

8.   A firing position slightly forward of the target’s beam is naturally the more favorable for attack. However, submarines, knowing that the most attention was given to this sector by the lookouts have recently been attacking from a firing position slightly abaft the beam, so that this area must not be neglected.

9.   A submarine attacking at night will run on the surface; if there is moonlight, the submarine will probably approach from the direction away from the moon, so that the target will stand out clearly, while the submarine will be invisible. The submarine will prefer to approach from abaft the beam of the target ship, so that she will not be in danger of being rammed. There is naturally more danger of being rammed at night on the surface than during the day when submerged. On a dark night, a ship may run upon a submarine charging batteries on the surface and take her by surprise.

10.  During twilight submarines have an especially fine opportunity to attack. They will attack submerged and probably from the darkest part of the horizon.


1.   All officers should look upon the actual sighting of an enemy submarine not as something to be avoided but as an exceptional stroke of good fortune for them. They would look forward to this encounter as a priceless opportunity which may never come again, an opportunity to test in actual warfare the results of years of study and work. In order to take the maximum advantage of this opportunity, officers will repeatedly rehearse mentally their actions under all possible conditions until they can instinctively do the right thing. This training can best be obtained by studying the results of “Anti-Submarine Tactical Game”. They should consider that a submarine is continually operating in their area and that it may appear at any instant. They should be prepared for every emergency.

2.   All guns will be kept ready for instant action.

3.   During daylight sights will be set at 1000 yards; during darkness they will be set at 300 yards.

4.   Ammunition will be kept at all guns sufficient to last at the most rapid rate of fire until additional ammunition can be provided from the magazines.

5.   On small vessels, like EAGLE and DOROTHEA, at least one gun’s crew will be ready in the immediate vicinity of the forward gun or guns. If possible, one gun’s crew will be stationed at the after gun or guns in addition, especially if submarines have recently been reported in the vicinity.

6.   On larger vessels two gun’s crews will be constantly on watch, one in the vicinity of the forward gun or guns and the other in the vicinity of the after gun or guns. If the ship has one gun forward and one aft which bear on both broadsides these guns will be manned by the crews in case of action. If the ship has merely a broadside battery, each gun bearing on one side only, the forward and after guns on the side which the submarine is sighted will be manned by these crews.

7.   As soon after the alarm as possible all guns will be manned.

8.   The Depth Charges and Y-gun will be ready for instant use. The Depth Charge crew will be continually on watch in their immediate vicinity, ready to drop charges or fire the Y-gun instantly on orders from the bridge. An efficient means of communication between the bridge and the man at the depth charges must be provided. Depth charges will be set at 100 feet, but this may be changed by orders from the bridge at the time of firing. While depth charges should de [i.e., be] securely lashed and covered with canvass raised from the charges so as to allow an air space to prevent their being reached by the direct rays of the tropical sun, these arrangements should not delay the firing of the charge for more than one minute from the time the alarm is given.

9.   The crews of guns and depth charges will be stationed as deck lookouts in the immediate vicinity of their guns or depth charges until the alarm is given.

10.  As many additional lookouts as possible will be stationed on the bridge and during daylight in the tops. All lookouts will be assigned definite sectors to which they will confine their search. Glasses will be provided for as many lookouts as possible.

11.  The lookouts in the tops should devote part of their attention to the horizon, when they should look for submarines on the surface. They should also watch for the wake made by a submarine’s periscope or conning tower in the area moderately close to the ship--up to about 3000 yards. If the sea is calm a greater distance than this should be covered; if it is moderately rough with many whitecaps it will be best to confine the search of these lookouts to an area within 2000 yards of the ship. The periscope itself will be difficult to see, as it will have the water for a background. Top lookouts should also watch for torpedoes approaching the ship.

12.  Lookouts on the bridge and decks should watch for periscopes and conning towers against the sky background, thus covering an area between 2000 and 10,000 yards distant from the ship.

13.  At night the lookouts should watch for submarines on the surface close aboard and especially in the direction away from the moon.

14.  Lookouts during twilight should watch for periscopes close aboard and in the direction where the horizon is darkest.

15   The greatest possible number of watertight hatches and doors will be kept closed and preparations will he made for the immediate closing of any which must normally be kept open.

16.  The positions of all men-of-war, convoys and enemy submarines in the vicinity must be kept track of on the chart. This information will be invaluable for warning merchantmen, relaying radio messages, calling for assistance, or proceeding against enemy forces.

17.  On the larger vessels two officers will be constantly on watch. One of these officers may be assigned to ship control, while the other controls the fire of guns and depth charges. The Senior of these officers will be responsible for all operations against submarines until the Commanding Officer arrives on the bridge[.] On smaller ships two officers will be on watch when submarines have been reported in their vicinity.

18.  If possible, keep the wind and sun as far aft as possible, thus forcing the submarine to attack under unfavorable conditions.

19.  All officers and lookouts will familiarize themselves with the “Rules for Submarines” given in “U.S.Submarine Recognition Signals”.1 Several of the more important principles given in this publication are as follows:

(a) “The onus of avoiding contact lies with the submarine.”

(b) “The submarine in diving condition (no one on deck, masts down) should be treated as an enemy unless the proper deck and conning tower identification marks are displayed, or one of the correct signals is made.”

(c) “All periscopes will be treated as hostile, no matter where seen, by all vessels which are by order required to avoid submarines, and also by all other craft unless the periscope is recognized as friendly or the known position of our submarines make it probable that the submarine is a United States submarine. In the latter case, the periscope will not be attacked unless an enemy has recently committed some hostile act in that vicinity.



1.   Enemy submarines in the Western Atlantic are operating at great distances from their home bases. While the large cruising submarines which will be used for such operations carry great supplies of fuel and stores, these must nevertheless be carefully husbanded. While a great supply of ammunition will be carried, the submarine commander will probably not wish to expend large quantities of it in a protracted engagement on the surface; he will be especially careful of his use of torpedoes. As he has few facilities for repairs he will not wish to run for maximum speed for long periods on account of the possibility of breakdowns and he will not usually engage in a gun duel on the surface on account of the possibility of a chance hit.

2.   Enemy submarines will therefore operate with caution. They will rarely attack naval vessels, especially with gun fire, even if the submarines are greatly superior in gun power. This caution will be increased if our naval vessels always take the offensive against them. When our naval vessels are “dazzle” painted, submarines will have great difficulty distinguishing them from merchant vessels, and consequently will use great caution in attacking “dazzle” painted merchant vessels.

3.   Enemy submarines will attempt to fire torpedoes from a position between the bow and quarter of the target ship and distant about 200-500 yards. The torpedoes used will probably have a moderately short range, the high speed of about 38 knots, and a very large explosive charge. Direct bow and stern shots and 90 degree angled bow and stern shots will be used.

4.   After firing a torpedo, German submarines are instructed to take either of two courses:

(a) To submerge immediately to 148 feet and run for fifteen minutes, presumably at high speed.

(b) To keep periscope a few inches above the surface and to watch the results of the shot, and the counter maneuvers of the enemy. Then submerge to 148 feet and run for fifteen minutes.

5.   When firing at a single ship German submarines are instructed as a general rule to turn until they are on an opposite course from the target after firing. Assuming a firing position on the starboard side of the target, their courses of action after firing will probably be as follows:

(a) Direct bow shot from abeam---Turn slightly over 90 degrees to the left and steady on a course opposite to that of the target.

(b) Direct stern shot from abeam---Turn slightly less than 90 degrees to the right and steady on a course opposite to that of the target.

(c) Angled bow shot from abeam (submarine on a course parallel to the target)---Turn 180 degrees to the right and steady on a course opposite to that of the target.

(d) Angled stern shot from abeam (submarine on a course opposite that of the target)---Hold a steady course opposite to that of the target.

(e) Direct bow shot from broad on the bow---Turn about 45 degrees to the left until on a course opposite to the target; after one minute’s run turn 45 degrees to the right to the original course of the submarine.

(f) Direct stern shot from broad on the bow---Turn about 180 degrees to the right steadying on a course opposite to the original course of the submarine.

(g) Angled bow shot from broad on the bow (submarine on a course about 45 degrees to the left of that of the target)---Turn right through an angle of about 225 degrees and steady on a course opposite to that of the target.

(h) Angled stern shot from broad on the bow (submarine on course 135 degrees to the right of the target’s course) Turn about 90 degrees to the right and steady on a course about 135 degrees to the left of the target’s course.

(i) Direct bow shot from on the quarter---Turn about 135 degrees to the left and steady on a course opposite to that of the target.

(j) Direct stern shot from on the quarter---Hold steady course.

(k) Angled bow shot from on the quarter (submarine on course about 45 degrees to the right of that of the target)---Turn to the right through 180 degrees and steady on a course opposite to that of the submarine’s original course.

(l) Angled stern shot from on the quarter (submarine on course about 135 degrees to the left of target’s course) Turn to the left about 45 degrees and steady on a course opposite to that of the target.

6.   When a convoy is escorted by one naval vessel, as would be the case should the convoy system be used in the Gulf of Mexico, the submarine will probably select for a target the merchant vessel farthest away from the escort. Thus if the escort should be at the rear of the formation, the leading vessel will probably be attacked, the submarine running away after the attack on a course at right angles to that of the target. If the escort is at the head of the formation, a rear ship will probably be attacked, the submarine running away after the attack at a course opposite to that of the target. In attacking a convoy submarines have instructions not to fire at a range of less than 500 yards. A common form of attack, recommended by the instructions, is for the submarine to head for the interval between two ships in an outside column; when a range of 700 yards is reached, a direct bow shot is fired at the leading ship of the two so that the course of the torpedo makes an angle of 50 degrees with the course of the target; then a 90 degree angled bow shot is fired at the rear ship.

7.   The maximum speed of a submarine under way will seldom exceed eight knots, and this speed will not be maintained for long. The tactical diameter submerged will be from 400 to 500 yards. For submarines of the U-Deutschland class, this diameter will probably be considerably greater. While a submarine may turn while diving, this will probably triple the time to reach a set depth, as putting over the vertical rudder tends to bring her to the surface.


1.   Decide whether or not to treat the submarine sighted as an enemy.

2.   Always act vigorously on the offensive, absolutely regardless of how inferior you may be to the enemy submarine.

3.   Fire one gun in the general direction of the submarine. This gun is the signal for General Quarters and indicates the position of the submarine. Should the submarine be discovered by a deck lookout, the gun captain is authorized to decide whether or not to treat the submarine as an enemy and to fire the first gun on his own initiative, provided the submarine is clearly seen close aboard so as to make immediate action imperative, and that submarines have recently committed hostile acts in that vicinity.

4.   In the great majority of cases where submarines have been reported, buoys, spars, boats, floating wood and even our own patrol craft have been mistaken for them. Everything of a suspicious character should be immediately reported to the Officer-of-the-Deck, who should exercise reasonable care in opening fire, especially where this might involve damage to our own vessels. However, in case of doubt, fire will be opened, as it will be better to open fire ten times when a submarine is not present, than to allow it to escape once by a failure to commence firing. This is especially true at night or when the visibility is poor, for then there will be opportunity for only one or two shots.

5.   Immediately after the first gun is fired, a rapid fire of all guns which will bear will be opened on the submarine.

6.   Course will be changed immediately in the direction of the submarine, taking care, however, not to steer a course such that any guns, which are delivering an effective fire, will be prevented from bearing on the submarine.

7.   If the submarine comes to the surface with the purpose of fighting a gun duel, close the range as quickly as possible and ram.

8.   If the submarine submerges run toward its estimated position and drop depth charges.

9.   The lookouts in the tops will attempt to follow the submarine’s course under water. At a distance of 500 yards a submarine should be seen when the top of the conning tower is about 10 feet under water. A track of oil sometimes comes to the surface; this gives an exact indication as to the submarine’s position. On a moderately smooth day the track of the air bubbles from a torpedo will indicate a positon of the submarine when the torpedo is fired.

10.  If there are none of these evidences of the submarine’s position, the officer responsible for the handling of the ship will in general accord with the principles laid down under the “Enemy Forces” make an estimate as to the most probable course of the submarine, maneuver the ship accordingly, drop depth charges and fire Y-gun at the times when in his opinion the greatest damage will be inflicted upon the enemy. All officers will be drilled in the depth charge attack under all possible conditions by frequent work with the Anti-Submarine Tactical Game.

11.  Should a ship be torpedoed a careful watch should be kept for the reappearance of the submarine. If it becomes necessary to abandon ship, one gun’s crew should remain concealed in the vicinity of their gun to the last instant in the hope that the enemy submarine will reappear and the opportunity for a shot at her be presented.

12.  Should a convoy be protected on one side by land or shallow water, the escort vessel will take position on the outboard flank oppo.ite the center of the convoy. During daylight the escort will maintain steam for maximum speed, or in the case of Salem 20 knots, provided this is permitted by logistics. During darkness steam for only three knots above the speed of the convoy will be required. While coasting a hunting group temporarily assigned to escort duty will take a position 3 to 7 miles on the outboard bow of the convoy, stopping to listen at frequent intervals. Upon hearing an enemy submarine, the hunting group will be considered as entirely relieved from escort duty and will trail and attack the submarine.

13.  When a convoy escorted by one vessel is proceeding through an area where submarine attacks may be expected from either side, it is recognized that the chief role of the escort is to prevent submarines attacking with guns. However, measures must be taken so as to give the most efficient protection possible against torpedo attack also where submarines have been attacking convoys with torpedoes. The most effective means of accomplishing this is to use the irregular zig-zag described in O.N.I. Publication No. 30.2 This zig-zag should be laid out so as to place the wind and sun as far aft as possible. The escort should take position on the flank where conditions would be the most favorable for torpedo attack. In case a submarine is sighted making an approach one depth charge should be dropped immediately for the moral effect it may have on the submarine. A submarine making an attack has not usually an opportunity to sweep the horizon on all sides and the discharge of a depth charge may bluff the enemy into believing that a naval vessel which he cannot see is close upon him. This may make him desist for making the attack or cause wild firing of torpedoes.

14.  Should a convoy at sea be escorted by a hunting group, this group will take position from 3 to 7 miles ahead of the convoy. If two hunting groups are with the convoy they will take similar positions on either bow. Upon hearing a submarine the nearest group will trail it and make the attack. If only one submarine is known to be in the vicinity, the second group will follow in reserve, to complete the attack after the first group has exhausted its depth charges. If two submarines are known to be in the vicinity, the second group will continue with the convoy.

15.  If the convoy is provided with a permanent escort of one vessel and a temporary escort of one or two hunting groups, each of these forces will act as though it alone were present, following the instructions in Articles 13 and 14.

16.  Whenever there is the slightest opportunity of inflicting damage upon the enemy depth charges will be used with the greatest profusion. Depth charge attacks usually have a greater moral than material effect. If one charge out of one hundred inflicts material injury, the work of the attacking vessel is considered satisfactory.

17.  Attacking vessels should not leave the vicinity after making an attack with depth charges until it is practically certain that the submarine is either destroyed or has escaped.

18.  As soon as contact with a submarine is made, a contact report, make out in accordance with Fleet Standing Order No. 10, will be broadcasted. Later a detailed report of the encounter will be made in cipher to the Detachment Commander.

19.  The Detachment Commander expects all vessels to be handled with energy, decision and initiative. The results of the first encounter with the enemy will have the greatest effect upon the morale of our own and enemy forces. Every effort must be made to gain initial success.

Source Note: D, DNA, RG 45, Entry 520, Box 340.

Footnote 1: This document has not been found.

Footnote 2: This document has not been found.

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