Lieutenant Commander James T. Alexander, Commander, PORTER, to Captain Henry H. Hough, District Commander, Brest, France, and Commander, Squadron Three, Patrol Force
19 October 1918.
From: Commanding Officer.
To: Flotilla Commander.
Subject: Offensive tactics for destroyer escort.
Reference: (a) Force Comdr. circ. let. # 87 of 2 Sept. 1918.
(b) Comdr. U.S.N. Forces in France let.
1. The following suggestions are proposed for next conference in order to prepare escort to:-
(a) Deliver effective attack on enemy.
(b) Keep contact after first attack.
(c) Coordinate part units so engaged.
2. It is assumed that contact is made visually or by enemy hostile act against convoy and at least three destroyers attack under three conditions:-
(1) Submarine sighted in danger area.
(2) Submarine sighted at considerable distance.
(3) Torpedo wake or hit observed.
3. It is proposed in case a destroyer sighting submarine is favorable position for attack on convoy a depth charge be let go immediately; each destroyer on the flank dropping one at same time if no ships are in close proximity astern. This to be in addition to prescribed submarine warning. Radio to escort being broadcasted en claire “Sub sure”.
4. Attacking destroyers is one next ahead and next astern with sighting destroyer and as many others as escort commander can spare; maneuver on courses set by destroyer giving alarm until a flag hoist can be made giving 1st. bearing, 2nd. estimated courses of enemy, 3rd. commence firing. All destroyers should attempt to form an approximate line. It is believed that under above conditions not more than 10 charges should be expended on this maneuver. Depth charge setting should be gradually increased if sub was closed quickly. Destroyers arriving after 3 minutes should maintain deep setting on charges at least 100 ft.
5. In order to provide room for quick maneuvering, should leader wish to counter march, distance and interval should be such to permit turning with hard over rudder. In order to obviate chances of turning into barrage of nearest ship in addition to flag hoist cease firing a conventional signal of four whistles or siren blasts repeated by all should be arranged for. The attack should be flexible enough to permit any unit sighting enemy after attack was begun to become leader merely vy [i.e., by] visual or radio signal “Quack”. In this connection any successful attack must depend on rapid communication and necessity demands a few but easily understood flag hoists. It is suggested that a straight away course under above conditions would permit effective coordination by other destroyers and the laying of a curved pattern would not be necessary. This attack then should be called plan “A” to be followed instinctively by all destroyers when given approximate location.
For instance the leader beginning barrage immediately after 1st. charge would be sufficient indication to all that plan “A” was to be followed.
6. The conditions of contact as outlined above being rarely met with, a plan for attack when enemy is sighted at considerable distance, should be arranged. In this case considerable time must elapse before destroyers can arrive at the probably position.
7. Such wide limits are involved to make it necessary to formulate combined search and hunt before attack can be delivered. It is assumed that submarine sighted within 5000 yards has missed an approach and is seeking position for a browning shot. Study of the pamphlet ONI #23 of December 1917 shows the limits of a browning shot to be 1500 to 3000 yards. Owing to difficulty in approximating distances at sea, it is believed that an attack founded on a retiring search curve to be most effective within limits of 5000 yards. The submarine curves and maneuver board as developed by Commander [Louis C.] Farley, U.S.S. ALLEN are suggested for adoption. These curves based on data obtained from maneuvers of ALLEN with A L subs off Berehaven are considered the best available data on which to formulate a search.
8. To render successful an attack against enemy sighted within 5000 yards and beyond 1000 yards four destroyers an additional appears necessary for this plan sighting destroyer will be called #1, next astern #2, next ahead #3, and the fourth to be designated by escort commander #4.
The area surrounding point of submarine is divided into four sectors, i.e. 1-2-3-4. (See Fig. 1.)
The tracking board as proposed by Commander Farley, U.S.S. ALLEN would be used on each ship.
9. In event of 4th. destroyer not being detailed, No. 1 should turn to bomb sector 4, then proceed to No. 1. Enemy tactics if two subs were operating would be probably to draw off escorting force to long distance as possible to permit mate to attack from ahead and the detail of fourth destroyer would depend on circumstances.
#(1) Sounds warning broadcast or signals bearing and range and proceed to sector No. 1, dropping marker when arriving at estimated point of submergence and begins barrage on retiring search curve.
#(2) and #3 proceed to respective sectors and cover same with barrage on retiring search curve.
The line of bearing signalled by No. 1 will always divide sectors Nos. 1and no. 4.
The use of tracking board is recommended for use in this plan. Its operation depends on estimated data which is probably in error, but it appears to be better than eye and stop watch, a method also subject to gross errors. Depth charges to be expended on rather wide interval on submarines minute curve. Number of charges should be limited to about fifteen. Destroyers laying barrage should haul down warning flags when completed and slow to 15 knots, covering sector on widening legs. In this plan sufficient time permits senior officer taking charge. Signals for plan “A”, if submarine breached during barrage, could however be made by sighting destroyer.
The chances of No. 1 locating slick left by submerging enemy are good and undoubtedly no. 1 would be far enough ahead to signal corrected bearing and distance without affecting attacking force.
10. All ships, completing barrage, would immediately prepare to listen, standby and execute being sent out by S.O. [i.e., Senior Officer] each would stop, back, stop, listen and keep all machinery stopped maximum time (2 to 3 minutes) and at least all auxiliaries slowed for 5 minutes. Radio reports of observation bearing or K C (negative contact) being sent. Group maneuvered by S.O. until contact was made, then plan “A” or “B” until enemy located or search abandoned.
11. Some reasons for adopting a barrage of above nature should be stated. 15 to 20 charges must be widely scattered to cover maximum position. Radio communication en claire low power is necessary for rapidity and wide distribution of force. Plan should provide all units being ready for listening state as soon as possible after barrage. Barrage is necessary to speed up the enemy in order to keep contact by bearing. Usual hunting tactics would then be followed.
12. The next condition to provide for would be submarine sighted on horizon or between 5000 to 14000 yards distance. To render an effective search more than four destroyers appears necessary. A scouting force of three ships at least should proceed at high speed to approximate location, the force proceeding to greatly increased sectors as propsoed in plan “B”. Morring board and stop watch should be used in getting to sector allowing a submarine some average speed, say 8 knots. The usual hunting tactics are to be employed when sound contact is made. Dropping of a few charges on arriving in area and coordination in listening to be made as in plan “B”.
13. The last condition to cover is the one most frequently occuring, i.e. enemy presence detected by torpedo wake or hit. The plans to cover this situation have been formulated by use of L.V. Change aux in “Notes on Submarine Attack with appended sketches” recently issued to destroyers. It seems that the tactics he proposes are sound and could be adapted to a plan “D” with some modifications, In any plan provision must be made for a stern tube shot and the authors diagram fulfill this condition.
It is assumed that the enemy fires within 3000 yards and as set forth by Commander U.S.Forces in France letter of the quartering shots seems popular. Therefore flank and stern destroyers should form as in plan “A” using wake as seen as line of bearing to signal. Destroyers should set course on slightly diverging lines to permit use of bomb throwers [i.e., depth charges]. The prevailing opinion appears to be that the enemy will turn astern. A listening maneuver should be made immediately after last destroyer has completed barrage. Interval being at least 2000 yards to insure making contact.
14. It is suggested that the above plans would be useful in laying a barrage of the tactical antennae mines as set forth by planning Section notes dated August 17, 1915, (memorandum #41).
/s/ J. T. ALEXANDER.