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William S. Sims, Commander, United States Naval Forces Operating in European Waters to Base, Detachment, Squadron, and Division Commanders, and Certain Ship Commanders

S E C R E T.


U. S. S. MELVILLE, Flagship.

London, August 17, 1918.

     1.   The within paper, prepared by the Planning Section of the Force Commander’s Staff (as Memorandum No. 41) is a resume of enemy submarine tactics and of the conditions that govern his operations together with comments and suggestions as to anti-submarine methods.

     2.   Nothing in this paper is to be regarded as in the nature of orders or instructions: it is issued for information only.

                        /s/ Wm. S. SIMS.

                            Vice Admiral, U.S. Navy


Issued to:

Base, Detachment, Squadron.

and Division Commanders,

Military vessels commanded by

Officers of the regular Navy.


          We need to consider the following concerning enemy submarines.

(1)  Tactical Characteristics.

     (a)  Ability to rest on the bottom for 72 hours.

     (b)  Ability to remain submerged underway

              60 hours at 1 to 2 knots.

              36             2 knots.

     12        12             5 knots.

               3             7 knots (STERRETT, 7 hrs at 7 knots)

                         11 knots.

(c)  Increasing ability to run nearly silent when


     (d)  Surface speed 10 to 16 knots.

     (e)  Ability to submerge in 20 to 90 seconds.

     (f)  When submerged can hear pursuing vessels.

(g)  With upper end of periscope showing, hull is too deep for torpedo running at 25 feet, the maximum depth for setting.

(h)  Torpedo range is limited to 3000 yards. The most favourable range is about 300 yards.

(2)  Operating [Areas].

     (a)  English Channel and Irish Sea. Submarines can bottom.

     (b)  West coast fo France and the Atlantic. Submarine cannot bottom.

     (c)  North Sea. Can bottom in places, but not on the northabout route.

     (d)  Mediterranean Sea. Submarines cannot bottom.

     (e)  U.S. Atlantic Coast. Submarines can bottom, but as a rule U-boats never bottom - only the smaller boats bottom.

Converging points are still favourite hunting grounds. Good weather permits off-shore work. Bad weather and long nights bring the submarines into narrow sheltered waters. Large submarines prefer deep water, and water not frequented by patrol craft. We may expect operating areas to be extended in order to create corresponding extension of the escort system and prevent the formation of hunting units. The submarine does not like to be hunted. It much prefers to determine for itself the time when all hands must be on the alert.


German Submarine Situation.  1 June 1918.







yet operat-ing

Total in Actual Com-mission







Total remain

ing in Com-mission


Not Ident-ified





















































          On April 20, 1918, enemy submarines were distributed as follows:-



Home ports . . . .77


Flanders . . . .  24

Adriatic . . . . .43

Constantinople . .21  X

      TOTAL      165

X (Include 4 captured Russians)

4.   (Submarine Tactics.

          The following are extracts from the German Submarine Manual:

Torpedo Firing from Submarines.

          “Assume that firing at a range of over 3000 metres (3280 yards) is useless, and therefore better not attempted (for single boats

          The rule for submarines remains as before - Proceed unobserved to a position from which a high speed shot can be fired and a hit certainly obtained.

     1.   Most favourable Side for Attack.

          When choice is possible, the sunny side should be chosen, particularly when the sun is not too high, and provided the shot can be fired more or less from the direction of the glare of the sun.

          In a strong breeze the weather side is preferable.

     11.  Strength of Wind and Sea.

          Do not fire in a calm with a perfectly flat sea (except from the direction of the glare of the sun or at a slow cargo steamer).

          Force of wind 3-4 and sea 2-3, present the most favourable conditions for attack.

          If the sea is 5-6, when it may be just possible to fire, fire at right angles to the direction of the sea.

          Do not attack in a heavy sea and a long Atlantic swell.

     III. Use of Periscope.

          Perscope showing 1.5 to 2 m. cannot be seen more than 4,000 m., provided a suitable speed is maintained and the favourable side for attack is chosen.

          With binoculars it has not been possible to distinguish the periscope even at 2000 m.

          An unseen attack (periscope use sparingly) implies keeping the periscope low and showing it frequently but for quite short periods, (a few inches of periscope only, so that the object glass is almost awash).

          You must not for any length of time omit to take a look round.

          Lower the periscope completely and go to a depth of 18 m. (59 feet) when high speed (full speed or utmost speed) is necessary to attain the position for firing.

          Never show two periscopes at the same time.

          Come to the surface with periscope lowered.

          Handling of periscope immediately after firing.

(a) Lower the periscope and dive to the greatest possible depth (45 m.) (148 feet); this applies to particularly to small boats with only one periscope.

          A better method.

(b) Observe the shot and the hit! also whether a second shot is necessary and possible. For this purpose, after firing show the periscope as sparingly as possible in every way; that is, show very little of it, and as the boat invariably rises somewhat, always first lower the periscope a little; then raise it again according to your depth.

After observing the hit and the counter measures adopted, then (and not till then) proceed for about 15 minutes at the greatest possible depth. Lower the periscope completely and preserve silence in the boat.

IV.  Speed when Attacking.

     The speed of the submarine is a vital factor in an “unseen” attack.

1.   To close the enemy, first proceed at high speed until the bearing does not change. When actually attacking, endeavor to limit yourself to the lowest speed at which the boat keeps her depth well.

2.   Before using your periscope, always reduce speed.

3.   If the enemy is zigzagging, it is advisable not to proceed at too low a speed.

V.   Firing Range.

     The most favourable firing range is 200 to 300 m. (219 to 328 yards).

     It is advisable, in addition, after firing to turn away in the direction of the enemy’s stern.

Note. On the active service the most favourable firing range in the case of ships with which you are not absolutely acquainted, is 300 m. (328 yards).

     When attacking ships in a formation do not fire at less than 500 m. (547) yards range, particularly if the vessels are disposed towards you.

(a)  Do not fire at less than 170 m. (186 yds) in the case of a direct bow or stern shot.

(b)  Whitehead Torpedoes must not be fired at a range of less than 250 m. (273 yards).

     For a long range shot, only a quadruple salve promises success and then only under 3,000 m. (3,281 yards).

Procedure when pursued with Hydrophones.

     1.   A rough sea is the best natural protection.

     2.   The reduction to a minimum of the sounds caused by your own boat is an effective protection.

(a)  Connect the vertical rudder and hydroplanes for hand working.

(b)  Stop your ballast and trimming pumps. Use compressed air in lieu.

(c)  Let your main motors run at the lowest possible number of revolutions, stopping frequently. Keep the boat trimmed on the periscope.

     3.   Proceed at a depth of 45 m. (148 ft).

     4.   It is better to keep near the coast than out in the open sea in cases where the depth is greater than 70 m. (230 ft).

     5.   Lying on the bottom is a good way of evading hydrophone pursuit provided that the hull is absolutely tight.

          No leakage of air, and abobe all, no oil bulles bubbles.

     6.   Make the most of your time when your pursuer is going ahead, in order to increase your distance from him.

          The submarine must, however, stop frequently to listen, even at the risk of not increasing her distance from the enemy so rapidly.

          When attacked and force[d] to submerge, a submarine may :-

     (a)  Attempt to escape by proceeding at maximum speed.

     (b)  Proceed at slow speed.

     (c)  Proceed slowly, stoping and balancing occasionally to listen or to synchronise with stops of hunting units.

     (d)  Bottom (in water 40 fathoms or less).

     (e)  Anchor submerged.

     When making an attack on a vessel or convoy, a submarine normally must submerge a considerable distance away, and then manoeuvre while submerged for position. This may require the use of high speed and consequently exhaust much of her battery power.

     By day in crowded waters, or in localities where our own submarines operate, or our patrols are thick, the enemy must spend most of the daylight hours submerged, and devote much of the night to recharging batteries. Recharging may be done while proceeding on the surface at moderate speed.

     5.   General Intentions of Enemy.

     (a)  To continue submarine warfare to the end. Its effect is still of the first importance. To give up submarine war on commerce would be a blow to enemy prestige.

     (b)  New construction will probably be stronger, to permit deeper diving and towithstand better the effect of underway explosions.

     (c)  Will attack points of weakness, like slow convoys, vessels in areas where escorts are thin.

     (d)  Will give greater attention to submarine cruiser warfare. The recent trip of U.151 to American waters accounted for more than one-fourth of the tonnage sunk last month.1


     We should consider here the types of the vessels available, and the success that has attended different kinds of effort. The types of vessels available are :-

(1)  Destroyers.

Suitable for escorts, and for offensive work generally. Must depend at present principally upon sight contact. The Mason gear2 will enable destroyers to follow submerged submarine if close contact is made and submarine is not noiseless..Numerous depth charges.

(2)  Eagle Boats.

Special listening equipment. Suitable for off shore work. Primarily a sound hunting vessel, but sight lookout important. Should be able to keep the sea in all weathers.

(3)  Submarine Chasers.

Sound hunting vessel. Efficient in smooth water. Too small to keep the sea in rough weather and be efficient. Very apt to make sight contacts at night

(4)  P. Boats. Q Ships and Sloops.

Seaworthy. No special listening equipment. Depend on sight contacts.

(5)  Trawlers and Drifters.

Have some listening equipment - Fish Hydrophones.3 Stay out about four days, but seek shelter in bad weather.

(6)  Motor Launches and Coastal Motor Boars [i.e. Boats].

Suitable for work in quiet waters. Are being fitted with listening equipment.

(7)  Dirigibles.

Suitable for convoying and for scouting and reporting submarines, and giving information to surface vessels.

(8)  Seaplanes.

Suitable for patrol and attack on submarines; also for giving information to surface vessels.

(9)  Submarines.

Very good lookouts. Frequent contacts. Fault is in weapon - the torpedo - which more often than not misses its target. Excellent listening vessels.


          The following five methods have been most successful in sinking submarines, and neglecting all others, have been successful according to the percentages indicated :-

Gunfire. . . . . . 23%

Depth Charges . . .23%

Torpedoes. . . . . 21%

Ram . . . . .  . . 17%

Mines . . . . . . .15%

          (a)  Gun Fire, has largely been successful on close contact as at night, or in thick weather, or on Q ships.4 We may expect it to be less effective in future, due to the wariness of enemy submarines of approaching vessels that they think may be traps. The constant readiness of one or more guns on each vessel at night, joined to better distribution of information concering our own vessels in any given area should enable us to be quicker on the trigger at night, and consequently more dangerous to the enemy submarines. Every vessel should consider its guns its most effect anti-submarine weapon at night, and take measures accordingly. If each vessel can step up its gun fire efficiently against submarines 25% - a small increase the cumulative effect throught a very few months will be exceedingly valuable.

          (b)  Depth Charges are now considered the principal weapon for attacking submarines. Two or three thousand charges a month are used with only a small number of successes. The problem of the more efficient use of depth charges is one that requires the most constant and painstaking thought and organization of which the Service is capable. We cannot expect any revolutionary results, but if we can increase, by more careful methods, the efficiency of several contributing factors, we may very possibly increase total efficiency by 50%. If there be four contributing factors of efficiency, and if our present efficiency is represented by 80%; and if we by increased effort raise those factors to a 90% efficiency, we shall have increased our total efficiency by 60% plus. The following discussion may therefore not be out of place.

          When a submarine is sighted by an anti-submarine vessel in its near vicinity, there are several problems that must be solved correctly in rapid succession, in order that the submarine may be sunk by depth charges. The end in view is to explode a depth charge within 70 feet of the submarine. The problems requiring solution are in chronological sequences :-

(1)  Mark the spot on the surface of the water where the submarine was seen.


          It must be presumed that the submarine will submerge promptly, and leave no trace of its position. An unmarked spot on the surface of the water cannot be followed by the eye; therefore the inevitable result of a submarine disappearing below the surface is for the unaided eye to lose trace of the point of submergence. If the vessel on which the observers are, is obliged to turn through a considerable angle, the uncertainty of the submarine’s position when last seen is greatly increased. Numerous reports from both American and British sources indicate that many depth charge attacks take place at points quite distant from the submarine, because the position of the submarine when last seen could not be marked, and because it was in consequence wrongly estimated while manoueuvring for attack. The concensus of opinion is that the distance of the submarine is usually underestimated.

          No complete solution to these difficulties has been found. Ensign H.J. Nichols, U.S.N.R.F. of the U.S.S. EMELINE5has suggested a marker shell that can be fired at the submarine, which shall upon hitting the water will explode and leave a small smoke producer when the shell struck the water. If the fall of this shell is spotted with reference to the submarine, it should furnish a good guide to subsequent manoeuvres. A second or third shot may be spotted closer to the submarine. No shell of this nature is, as yet, developed. There is urgent need for such a shell.

          Lacking a marker shell, we must consider how best to solve the problem without it. We can always mark a line on which the submarine was seen by observing the compass bearing of submarine, and by dropping at the same time a buoy. If in addition an estimate is made as to the distance of the submarine, we obtain a valuable point of departure for all subsequent manoeuvres.

          The following rules should govern the dropping of the buoy :-

     (a)  Drop the buoy as near as possible to submarine; but drop it before submarine disappears.

     (b)  Note compass bearing of submarine at instant buoy is dropped.

     (c)  Estimate distance of submarine from buoy at instant buoy is dropped.

     (d)  Start stop watch at instant buoy is dropped.

     (e)  Note course of submarine with relation to line from buoy to submarine, then convert to compass course.

     (f)  Transfer data to mechanical mooring board.

     (2)  To manoeuvre into position for attack.


          The attacking vessel should work out in advance plans for approaching the submarine, based on all the typical positions and courses of the submarine with relation to the buoyed line of position, so that every officer will be ready instantaneously with the correct decision, no matter in what position the submarine may be, nor what course it may be steering. To be thus ready, may result in saving just that minute that will give success. The Commanding Officer of each vessel should hold school for officers on this and similar points.

          As the turning circle of submarine is smaller than that of destroyers; and as submarines almost invariably turn or zig-zag when they submerge to escape, it may frequently be advisable to head the attacking destroyer to a point one side of the submarine, such that if the submarine turns towards that side, a depth charge barrage will get him. The attack can then be continued along a retiring search curve towards the other flank in such manner that the first circle of the destroyer will cover 360° of the submarines possible courses, instead of 180° provided for by plan given in Force Commander’s letter of March 29, 191[8]6.

(3)  To drop depth charges in the most probably position of the submarines.


          There are two principal cases under this heading :-

          (a) Submarine leaves visible traces of oil or bubbles.

          (b) Submarine leaves no visible trace.

          In the first case the attacking vessel must -

(a) Determine distance ahead of oil or bubbles that submarine is.

This distance depends upon submergence of submarine and submerged speed of submarine. Submergence is always an uncertain quality. U boats dive voluntarily to over 300 feet. U 104 used 98 feet depth to escape, and 164-167 feet when forced to dive where mines were considered probable. Cruiser submarines dive to 492 feet, and are to be tested to 525 feet. At least one U-boat made a practice of remaining as near the surface as possible, in order to avoid depth charges, and in order to watch attacking vessels.

     As to speed submerged when being attacked, it appears most probable that a speed near the maximum, 9 knots, is used until a considerable distance is run from the point of complete submergence.

     Tables have been prepared giving the distance in yards the submarine is ahead of the oil or the air bubbles under various assumptions as to submergence and submerged speed. In order to determine the point for dropping depth charges, allowance has to be made for travel of submarine after bubbles or slick are passed, and until depth charge explodes. As the bow wave may obliterate the slick so that the depth charge officer cannot see it, it is desirable to mark the end of the slick by dropping a buoy from the bridge. The depth charge officer may then use this as a point of departure for his depth charge calculations.

          Depth charges sink 6.5 ft. per sec.

          Depth charges countermine at 245 feet

          At nine knots a submarine travels 5 yards a second, or 38.5 yards while a depth charge is sinking 50 feet - 2 1/3 times as fast as a depth charge sinks.

          In estimating course of submarine assume -

(a)  That if submarine is attacking, it will continue in an effort to get in its shot - and may not see attacking vessel.

(b)  That if submarine is escaping it will turn sharply, and will make wide sig-zags.

The following points have been emphasized by the Chief of Staff at Queenstown:-7

(1)  There should be on each anti-submarine vessel a Depth Charge Officer with battle station aft, who should supervise the handling, depth setting and dropping, of depth charges in accordance with signals from the Bridge. or according to his own judgement if signals fail.

(2)  There should be a depth charge crew; thoroughly organized and trained in handling, setting and dropping depth charges. This crew may be that normally stations at the after gun. The after magazine ammunition crew might be stationed to reload the Y-guns.

(3)  There should be an efficient system of depth charge signals from the bridge - capable of repeat back. Following suggested :-

                        Siren whistle signal.

                        Electric bell.

                        Electric gong.

                        Klaxon horn.

                        Ships whistle.

                        Air whistle.

     The following should be kept in mind :-

     Experience indicates that vessels almost invariably underestimate:

     (a)  Distance submarine is ahead of slick or bubbles.

     (b)  Distance travelled by submarine from point of submergence until attacking vessel arrives.

(c)  Distance travelled by submarine while depth charge is gaining its depth.

When submarine leaves no visible trace, entire dependence must be placed on calculations based on theoriginal observations and corresponding marks. Nearly all reports indicate that the desire of the C.O. of the submarine to have a look around, will bring the submarine up within half an hour. The best answer to this habit is special lookouts, and special vigilance after a daylight attack or a daylight sighting, and in the hope that a new point of departure may be thus gained.

As to methods of getting depth charges in the water.

These are :-


              Thorneycroft Throwers.

              Depth charge racks.

          For all dpt depth charge attacks made soon after the submergence of the submarine, the initial attack is of special importance, for then the position of the submarine is known better than it will be known until it is sighted again. Y-guns and throwers make it possible to enlarge the pattern of the attack. . . . . If a submarine appears inside the turning circle of a vessel, there is only one way to drop a depth charge near the submarine and that is to turn away and stand off until the submarine cannot get again inside turning circle before attack is delivered. Y-guns and throwers may throw depth charges towards the submarine and thus meet in a way this special situation. The usefulness of the thrower would be greatly increased if it could be trained.

          The consensus of destroyer opinion is in favour of more than one depth charge thrower on each vessel; of permitting a 300 foot depth charge settling; of carrying a few 600 lb. depth charges on the later destroyers.

          Radius of destruction of a 300 lb. charge is 70 feet; of a 600 lb. charge is 95 feet; 600 lb. depth charge weighs 800 lbs. Depth charge throwers capable of throwing a depth charge containing 260 lbs. T.N.T. 300 yards weighs about 4000 lbs.

     TORPEDOES. fired from submarines have been very effective against enemy submarines, but many opportunities for success have been lost through the difficulty of hitting so small a target as a submarine. Withthe enemy submarine showing its periscope only and probably in the act of diving, the torpedo set for 25 feet is apt to miss. Experienced officers believe that the depth setting should be changed to permit of a 60 feet setting. In-dependent, however, of depth of submergence, the submarine is a very difficult torpedo target. The problem of increasing the probability of torpedo hits is of extreme importance. There are two ways of increasing the probability of hits:

     (1) Firing more torpedoes.

Comment. It has been suggested that a small torpedo be developed that can be fired in groups simultaneously from the same torpedo tube - so directed as to scatter shot-gun fashion.

     It is of course assumed that every care is taken to keep each torpedo in efficient condition, and that on each occasion of a profitable opportunity to fire at any enemy submarines, every torpedo that can be fired effectively will be fired.

(2) Increasing the danger space of torpedoes.

Comment. Each torpedo carries an explosive charge, which, if detonated within 70 feet of a submarine, will sink or disable the submarine. Many torpedoes fail to hit the submarine, but still pass within 70 feet of it. It is probable that the number of successful shots would be increased not less than 50% if each torpedo passing within 70 feet of a submarine detonated. No other torpedo problem in design is of such immediate importance as the following :-

To attach to all torpedoes now used by submarines a device that will detonate the torpedo should it, while making a war run, pass within 70 feet of any vessel.

     The Run as a weapon needs little discussion here. Prompt bold seamanship is all that is required for its successful use. No captain should ever hesitate to ram if his vessel is strong enough to damage seriously the submarine. Every submarine sunk is ten million dollars a year saved to the Allies.

     Mines. The enemy submarines that have been sunk by mines have been sunk in fields of anchored mines. In previous studies we have pointed out the importance of making our primary mining effort barrages closing the exists to enemy submarine bases. No change in conditions has altered our opinion to the soundness of this policy. When mines are available over and above those required for barrage operations they may be used as deep trap mine fields in localities where submarines are apt to bottom, or where patrol vessels may force them to submerge. The danger that deep mine fields offer to shipping makes it advisable that mine fields should not be laid on traffic routes.

Where a surface mine field is laid as an anti-submarine measure, it should be above a deep mine field, otherwise the submarine will soon learn to dive under the surface mine field.

          The suggestions have been made that, since a small mine detonating in contact with the hull of a submarine will destroy the submarine, it might be profitable to attach to a single mooring rope as many as five 100 lb. horn mines of the existing type spaced twenty-five feet apart. This arrangement, although possibly difficult to lay, would economise greatly in wire rope, and might be considered a substitute for our antennae mine should an answer be found to that mine.

We must always consider the possible necessity of abandoning the antennae mine; and therefore should complete without delay up to the point of readiness for quantity production, a type of mine that does not depend in any degree for its efficiency on secrecy regarding its design.

The foregoing discussion on mines does not bear directly on the tactical use of mines in anti-submarine warfare. We shall now encounter the tactical use of mines against submarines.

The depth charge detonates without reference to the presence or absence of a submarine within its restricted area. If it is to be effective the depth charge must arrive at its set depth at a time when there is an enemy submarine within the radius of its destructive effect. When we consider the great number of depth charges that are expanded [i.e. expended] without definite known results, we are led to enquire if there be not some other more effective way of using underwater explosives. The following is suggested :-

A tactical antennae mine to be laid from anti-submarine vessels in a barrage around all submarines with which close contact is made. The present U.S. mine to be used as indicated in the sketch.8

The mine is suspended from the buoy. Forty feet of buoy rope makes the mine dead to surface craft. The buoy furnishes an additional safeguard to vessels navigating on the surface. The Antennae both up and down make the mine effective over the entire depth of any ordinary submergence of a submarine. The mine is not anchored, and must be arranged to sink after a reasonable period - saytwo hours.

Assuming contact with a submarine which permits locating the point of her submergence within 200 yards, and allows the attacking vessel to reach that point within three minutes, the submarine may then be as much as 1200 yards from the point of submergence when the attacker arrives on the scene. If the attacker carries 50 antennae mines, she can lay a minefield of about 2000 yards in length (at intervals between mines of 120 ft). Which will give a good chance of being exploded by a submarine passing through the field. By laying the field on a retiring search curve, as are of about 60° (starting on a 1200 yard radius) can be covered. We therefore will have one chance in six of selecting the proper area: or about one chance in eighteen of mining the submarine by a single destroyer. Judging from experience this chance is much greater than of successfully depth charging the submarine unless the submarine be seen. When tactical mine barrage should be particularly useful in the case of an attack upon a convoy, because -

(a) The submarine initially will be close to escort vessels.

(b) The approximate depth, speed, and direction which the submarine will take may be predicted with fair accuracy.

Large heavy vessels of the convoy might carry large numbers of tactical mines with a view to using them against any submarine attacking a convoy.

     The tactical value of mines would be greatly increased if they could be made to detonate whenever a vessel came within the radius of their destructive power. The antenna maybe be regarded as a partial and, possibly, temporary solution of the problem. A complete solution extending the sensitiveness of the mine 100 feet in all directions would be invaluable. It would reduce the cost and increase the practicability of barrage operations enormously, while it would immediately justify the adoption of the tactical mine as the chief anti-submarine weapon.

We recommend that the problem of a self contained mine detonator sensitive to vessels within a radius of one hundred feet be considered urgent and of great importance.


     Whenever possible, the attitude of the hunted, rather than that of the hunter should be impressedimposed upon the enemy submarine. Every time that an enemy submarine is forced to submerge, it enters a danger area where machinery accidents and errors of personnel produce their maximum effect.

     The fact that thirty-two enemy submarines have been lost through unknown causes is an indication of the value of making submarines navigate submerged.

Drive them under, keep them under.

     The tactical operations that we have to consider are :-

          (1)  Hunting by sound.

          (2)  Hunting by sight.

          (3)  Counter attack by escorts.

In all hunting operations it is essential that the services of information and communications be sufficiently and intimately co-ordinated with the hunting efforts, to the end that hunters may make frequent and timely contact with the enemy. There could be a constant inspection and checking of the communication system and a flexibility of hunting arrangements such that, whenever a submarine appears near the coast, it shall meet with a reception suited to its important character. Aircraft, surface vessels, and friendly submarines, must all have their efforts co-ordinated. There must be the freest possible flow of information to and from all units.

In general, hunting will be most profitable:-

(a)  In water over 40 fathoms deep, where submarine will not bottom.

(b)  Immediately after submarine has made an attack. (Battery power reduced).

(c)  After submarine has passed through a thick patrol (Battery power reduced).

(d)  At night in areas where, during the day our own submarines operate, or where there has been much traffic. (Battery power reduced submarine probably on surface).

(e)  After a submarine’s hull has been engaged to leak air or oil, or has been otherwise damaged by depth charges or other causes.

(f)  In narrow waters; requiring the submarine to make frequent observations for navigational purposes, and restricting his choice of courses while submerged.

(g)  Along routes of passage to and from operating grounds of submarine. The general course most to be taken after submerging can then be predicted.

(h)  For hunting by sound, in areas where there is little traffic.

     (i)  During summer; good weather and long days.

     The primary object of hunting by sight is to force the enemy submarines to remain submerged until she is compelled to emerge. Incidental opportunities for attack will of course be taken advantage of.

     Owing to submerged radius of submarines and to their ability to proceed unobserved, this form of hunting cannot be successful except that an area of at least 25 miles radius be placed under good observations.

     A submarine can proceed 25 miles submerged in 3 ½ hours at 7 knots 02batteries exhausted; 5 hours at 5 knots - batteries 40% exhausted; 12 hours at 2 knots - batteries 20% exhausted.

     A formation deployed so as to have an area of 25 miles radius under observations, with centre over last know position of submarine, will then have from 5 to 12 hours in which to sight the submarine before she can escape.

     Meantime if the submarine is sighted, the formation may move its centre over the new position and start afresh, with the advantage of having partially exhausted the submarine’s batteries - and perhaps of having shaken its morale by a depth charge attack.

     Aircraft and kite ballons would be of great assistance to the hunting group/ Listening devices also would be of great assistance.

     At dark, in fog, or at the end of the time when it is judged that the submarine may have reached the limit of observations without discovery, it will become necessary to move the formation in the supposed direction which the submarine may have taken, and at her assumed speed.

     For those reasons, this form of hunting will be most profitable in northern latitudes during the summer; and also along the route of passage between enemy operating ground AND BASES. Deep Water is essential to prevent the submarine economising power through bottoming.

     In order to cover an area 25 miles in radius, about 20 vessels are required with visibility of 5 miles. If vessels are equipped with Kite Balloons, able to see a submarine on the surface 15 miles, only six vessels will be required for observations; but they will require additional vessels to prevent the submarine from remaining on the surface for considerable periods of the time out of gun range from them, which periods he may utilize for recharging batteries.

     Owing to the necessity for driving submarines under promptly with gun the intervals between units of a group of hunting by sight, should not exceed 13 miles, even when equipped with Kite Balloons.

     22 vessels 15 miles apart can cover an area of 45 miles radius. If the centre vessel and the outer line carry kite balloons having visibility of 13 miles, but 14 of the 22 need to carry Kite Balloons.

     The enemy can reach the outer limits of observation starting from the centre of the formation in 7 ½ hours at 6 knots with batteries exhausted in nine hours at 5 knots with batteries 75% exhausted; in 23 hours at 2 knots with batteries 40% exhausted.

     If units of a sight hunting group are equipped with listening devices, the opportunities for obtaining information of the enemy’s approximate location will be increased. His escape on the surface, even at night, will be rendered difficult by this means.

Even in large group sight hunting, co-ordinated starting and stopping of the engines of all units will be essential if listening devices are used - although the sound interferences between units will not be so serious in the large sight hunting group, owing to the great intervals of deployment.

     Destroyers, Eagle Boats, P. Boats, are suitable units for sight hunting groups in the open sea. Trawlers, submarine chasers, Motor launches, and Coastal motor boats, are suitable units for sight hunting groups in sheltered waters.

     In general, the hunting procedure would be about as follows :-

     operations being conducted in Northern Latitudes during summers over deep water, and preferably along passage routes, and near any patrols that may be operative :-

     1.   Information received of submarine position nearby.

     2.   Deploy at 15 mile intervals with centre of formation over last known enemy pos[i]tion, getting kite balloons out.

     3.   Zig-zag at 15 knots about centre of formation.

     4.   Stop simultaneously about three times per hour for five minutes to listen.

     5.   Upon getting sight or sound contact, shift centre of formation over new enemy position, vessels making sound contact retaining it, and other vessels stopping and starting so as to facilitate hunting by sound.

     6.   Move whole formation in direction enemy is assumed to have taken, at such speed as to keep centre of formation over enemy assumed position.

     7.   If enemy is heard at night on surface, or charging batteries, search for him to drive under; closing intervals if necessary, and keeping formation centre near his last known position.


          A system of patrol of a large area by a few vessels generally speaking, is unprofitable. It is expensive in wear and tear and fuel; it is not an economical distribution of forces. Because areasin which the enemy is operating are covered no thicker than other areas; contact with the enemy depends largely upon chance; and evenwhen contact is made, there is sufficient force present to deal with the enemy efficiently.

          The most useful thin patrol is by means of our own submarines; whose operation will annoy and handicap the enemy (and occasionally damage him) by inducing him to remain submerged during most of the day, rather tan than risk a surprise torpedo attack.

          The next most useful thin patrol will be atnight, in area which the enemy is suspected of using to re-charge batteries.

          Air patrols will be useful in obtaining informations which will put our forces into contact with the enemy, and occasionally useful in attacking him.

          Thick patrols are very useful in narrow passages through which the enemy must pass frequently; provided the patrol has a formation of great depth, or is maintained over a deep mine field.

Convoy Counterattack.

     The opportunity normally presented for effective action against enemy submarines immediately following an attack upon a convoy, is so good as to warrant unusual efforts to take advantage of it.

(a)  There is present a large concentrated force of anti-submarine craft.

(b)  The position of the enemy submarine is near, and is usually known within narrow limits.

(c)  His probable immediate action may be predicted with fair accuracy.

     (d)  His battery power is usually reduced considerably.

     (e)  Usually the water is too deep for bottoming.

(f)  Immediate further danger to the convoy has been eliminated, except in the very rare case of another submarine being in the near vicinity. This possibility is so remote as not to justify serious consideration, until at least several hours have passed.

     Under the circumstances we are fully warranted in employing practically the entire escort force in a counter attack, and, should the counter attack fail, in search for a number of hours by a part of the escort. As destroyers become more numerous, it will be desirable to organize a part of each escort into a hunting group that shall leave the convoy upon contact with an enemy submarine, and shall thereafter hunt that submarine, until obliged to abandon the hunt to get fuel. The Antennae tactical mine already discussed, should be specially useful on escorting vessels.

     The frequency with which convoys get close contact with the enemy as compared to close contacts obtained in other way, may justify special hunting vessels, such as Eagle Boats, accompanying convoys in good weather through a part of the zone, in order that a hunt may be initiated under very favourable circumstances, No decision in this matter can be reached until the capabilities of these vessels are known more fully.

     In fast convoys, where vessels have on board experienced personnel, it is desirable that the vessels of the convoy carry a considerable number of depth charges, and that whenever the tactical situation makes the safety of the vessel lie in turning towards the submarine, that each vessel so turning shall use its depth charges freely. Important vessels manned by naval personnel should carry depth charges throwers.

Attack of Enemy Bases.

     The blocking of exits from enemy submarine bases by block ships has not been attended with sufficient success to justify effort. Destruction of enemy bases and of enemy vessels therein is valuable. The discussion of such efforts is outside the scope of this page.


     The United States is about to undertake a very extensive system of aircraft anti-submarine patrol.9 The success will depend very largely upon co-operation with surface vessels through an efficient communication system.



1.   To perfect services of information and communication, so that hunters will be given timely information of enemy submarines operating in their vicinity, and so that aircraft surface vessels, and friendly submarines may all have their efforts co-ordinated. There should be the free-est possible flow of information to and from all units.


2.   Every vessel should consider its guns and run the most effective anti-submarine weapons at night, or in thick weather and plan its actions accordingly.

3.   To determine experimentally the relative value of heavier depth charges; lashing two three-hundred pound depth charges together is suggested as a substitute for our 600-lb. depth charge


4.   To work the line on which close contact with a submarine was made by dropping a buoy and simultaneously observing the compass bearing of the submarine, and thereafter to use this line as an origin manoeuvre. See rules on page 8.

5.   To organize on each vessel a depth charge crew under a depth charge officer, and to give special attention to the training of those and to the system of signals and the doctrine governing their action. See page 10.

6.   To experiment with the antennae mine as a tactical anti-submarine mine, and to supply a part of all escort vessels with these mines as soon as developed. Large handy vessels in certain convoys to be used as tactical mine barrage vessels.

7.   To continue present plans for hunting by sound with chasers and submarines; areas for the latter to be separated from tother anti-submarine effort.

8.   To counter attack with a large force on each occasion when a convoy is attacked, and to continue to attack with a considerable portion of the escort. Drive the submarine under, keep him under, and impose upon him the attitude of the hunted instead of the hunter.

9.   To organise in each escort a regular hunting unit with definite plans of action.

10.  To organize sight-hunting units for operations in northern latitudes during summer, and along routes between enemy bases and operating grounds.

11.  To organize similar units of small vessels for narrow waters

12.  To use Kite Balloons whenever possible.

13.  To issue depth charges to vessels of fast convoys so that whenever the tactical situation makes the safety of the vessel lie in turning towards the submarine, it may use depth charges freely.

14.  To place depth charges throwers on transports and cargo vessels which have a suitable personnel.

15.  To direct submarines to use torpedoes freely upon every profitable opportunity for attack.


16.  To develop a marker shell that can be fired at a submarine about to submerge, which, upon hitting the water, will explode and leave a small smoke producer on the surface at the point of impact, is urgently needed.

17.  To design depth charge throwers so as to permit of variations of range and train.

18.  To develop as soon as possible up to the point of readiness for quantity production, a type of mine that does not depend in any degree for its efficiency on secrecy regarding its design.

19.  To develop a torpedo firing mechanism that will be sensitive to the presence of a vessel within 70 feet of the torpedo, and to attach this firing mechanism to all torpedoes used in anti-submarine warfare.

20.  To develop a mine firing mechanism that will be sensitive to the presence of a vessel within 100 feet of the mine, with a view to using this mechanism in anti-submarine mines.

Source Note: D, DNA, RG45, Entry 520.

Footnote 1: U-151 had arrived off the coast of Virginia on 21 May and remained there several days. On 25 May, it sank three American schooners, holding the crews for a few days. It cruised along the Atlantic coast laying mines and cutting two cables. On 2 June U-151 sank six vessels, including the 5,000 ton passenger liner Carolina. For more on its activities off the American coast and the U.S. response, see: Warning, 3 June; Benson to Sims, 3 June; Benson to Sims, 7 June; and Steps to Protect Shipping, 15 June 1918. A detailed account of U-151’s cruise is provided in Bell, When the U-Boats Came to America: 23-92.

Footnote 2: The M.V. or MV Device (Multiple Unit Variable Compensated Acoustic Tubes) was an advanced variation the K-Tube listening device developed by Professor Charles Max Mason. See: Norman Friedman, Fighting the Great War at Sea: Strategy, Tactics and Technology, 297.

Footnote 3: Fish hydrophones were a type of mechanical hydrophone towed behind ships to detect submarines. Hydrophones transmitted sound waves under the water and were a forerunner to modern sonar, although their effectiveness in World War I was limited. Still, Crisis at Sea: 327-330; Friedman, Fighting the Great War at Sea: 290-298.

Footnote 4: Decoy vessels, also known as Q-Ships or mystery ships were warships disguised to look like merchant vessels to lure U-Boats into battle.

Footnote 5: No further identification found.

Footnote 6: This document has not been located.

Footnote 7: Capt. J. R. Poinsett Pringle, Chief of Staff, Destroyer Flotillas, Queenstown.

Footnote 8: For a sketch of an antennae mine, see: August illustrations section.

Footnote 9: For an overview of anti-submarine aircraft patrol methods see, Rossano, Stalking the U-Boat: U.S. Naval Aviation in Europe During World War I, pp. 235-236.

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