Planning Division, Staff of Vice Admiral William S. Sims, Memorandum on Anti-Submarine Operations in the North Sea
S E C R E T.
MEMORANDUM ON ANTI-SUBMARINE OPERATIONS
IN THE NORTH SEA.
1. In a joint memorandum by the British and U.S.A. Planning Divisions, it was suggested that the attack on enemy submarines in the northern area should, under certain circumstances, be reinforced by strong destroyer forces from the Grand Fleet. (P.D.060 of 29/3/18).
2. This proposal was not approved because it conflicted with the policy of instantly reacting to movements of the High Sea Fleet; and the further objection was made the Grand Fleet destroyers would be unable to co-operate effectively with the hydrophone units.
3. However, the necessity for destroying submarinesx still dominates every other aspect of the war at sea, and the following proposals are made with the idea that offensive anti-submarine operations by the Grand Fleet may yet be reconciled with a reasonable condition of readiness for battle.
4. Grand Fleet destroyers are admittedly hard-worked, but any considerable increase in their numbers can only be justified by effective co-operation in the destruction of submarines. So long as the latter are allowed to pass uninterruptedly through the North Sea, they can choose their own place of attack and sufficient craft can never be provided to meet them. For example, the U.S.A. will only be following our own policy if they retain their rapidly increasing destroyer resources for escort work on the west side of the Atlantic
5. Whether the anti-submarine war, which continues day after day and year after year, does or does not culminate in a fleet action, the efficient use of destroyers depends upon using the maximum possible number of anti-submarine measures in the area where they are also available for a fleet action. Economy may also be effected by keeping the whole fleet assembled at one base and by such measures as protective minefields off the East Coast trade route.
6. Under the prevailing circumstances however, it would be inadvisable to weaken the destroyer forces outside the North Sea without some guarantee of successful results in that area and it is suggested that destroyers should on be withdrawn from other duties for the Grand Fleet in the proportion of 3x for every submarine accounted for by it per month. It would also have to be arranged to return a proportion of these additional destroyers to convoy work, etc., if the rate of destruction decreased with a corresponding increase in the sinkings outside the North Sea.
7. The first-class personnel, high speed, gun power, and sea-keeping qualities of Grand Fleet destroyers are in strong contrast with the under-manned, under-gunned and slow vessels employed on offensive anti-submarine work, and their position right on the flank of the inward and outward submarine tracks is also extremely favourable. Their systematic employment on this duty would also encourage the enemy to attack with surface craft and thus tend to bring about a fleet action under our own conditions of time and place.
8. It is suggested that, with the whole Grand Fleet assembled at one base and calls on its destroyers reduced as much as possible it would be practicable to employ a weak flotilla of about 12 destroyers continuously on offensive anti-submarine operations not more than 300 miles from the base and at the same time to maintain a sufficient number for escorting the fleet.
9. The daily average number of Grand Fleet destroyers available at Scapa and Rosyth between June 1st and July 25th was 80
o including days when the fleet or part of it was at sea. A proportion of the remaining 42 were employed on escort duty and sometimes the Commander-in-Chief despatched destroyers to patrol areas where sinkings had occurred. But the initiative always rested with the submarine and this will continue unless destroyers are used systematically and as an organized body to attack submarines on passage in the North Sea.
10. If this policy were approved and counting the 13th flotilla as two, a minimum of four flotillas, less the vessels escorting and refitting, would always be ready to accompany the fleet and there would be a maximum of two at sea, one of which would have sufficient fuel to co-operate in a fleet action provided the area of anti-submarine operations was on interior lines to the probable movements of the High Seas Fleet.
11. It is suggested that this routine should be frequently followed during the fine weather and the following measures are proposed. THE flotilla in conjunction with net drifters and a few hydrophone trawlers attack submarines on the same lines as the H. S. operation of October 1917x. With the fleet at Rosyth the mine nets might be laid on the suspected track between latitude 56° and 57° N, and with the fleets at Scapa between 57° and 59° N.
12. Lay a deep minefield and possible surface as well in the shallow area to the North-eastward of the Dogger Bank and control it by a Grand Fleet flotilla supported by a light cruiser squadron. So far as submarines are concerned the uncontrolled Heligoland Bight minefield has had its day
o. At the best it only diverts them to the Kattegat route which is less easily controlled.
13. When enemy submarines are passing by the gap between the Northern Barrage and the Orkneys, a flotilla might co-operate with other vessels to the south-westward of the barrage; or it might operate from Scapa or Rosyth with kite-balloons as an outpost force ready to act against submarines returning damaged or short of fuel.
14. The foregoing operations could be carried out without disturbing the battle organization of the flotillas and without any special material or training, but a responsible authority is required to co-ordinate the necessary craft and to initiate the operations. As they must all centre round Grand Fleet destroyers, it appears that the responsible authority should be the Commander-in-Chief, Grand Fleet.
15. If enemy surface craft appear in the North Sea a few signals suffice to get the Grand Fleet to the spot ready for action, but the co-efficient of delay between suggestion, plan, approval and execution if so great in the case of offensive anti-submarine operations in the North Sea that full advantage cannot be taken of fleeting opportunities. The question is mainly one of command. Someone should be responsible for attacking submarines in their passage through the North Sea and all the necessary craft should be under him when they are required for combined operations.
16. Experience shows that the location of submarines in narrow waters is comparatively easy but their destruction by trawlers and sloops is difficult. It is believed that this is due mainly to lack of speed in the hunting vessels and look [i.e., lack] of directional power in the hydrophones and that these difficulties can be overcome by hunting with several destroyers in company fitted with hydrophones on some such system as that given in Appendix II. It is suggested that about a dozen hydrophones and their operators be at once taken from trawlers and fitted in a Grand Fleet flotilla so that trials can be carried out.
17. Two sketch plans to illustrate possible anti-submarine operations by Grand Fleet destroyers are given in Appendix I. These are intended as examples only, the actual plans being left to the discretion of the Officer controlling the Operations.
Reference: Chart Attached.
A. Operations with Deep Mines.
Enemy submarines are being swept in and out from some point P in the vicinity of the South Dogger Bank Light Vessel (Lat. 54°46’N. Long. 4°10’E.), and are believed to be following the course PQx. Grand Fleet and all T.B.Ds. at Rosyth.
Temporarily cease mining the proclaimed area in the vicinity of P. Lay a deep minefield of H Mines on the shallow bank enclosed by the 20 fathom line, in a position through which the submarines are likely to pass in daylight. Occasionally patrol the vicinity of the minefield with a Grand Fleet flotilla. As an alternative a deep and shallow minefield might be laid here as it is within the enemy proclaimed area and outside the track of neutral shipping. The enemy laid a shallow minefield in the Kattegat outside their proclaimed area without even notifying it. Sinking plugs would limit any risk to our own ships. In case of attack by superior forces, the flotilla would retire with the assistance of a smoke screen.
Forces and Material Required.
A deep minefield of about 1000 mines to be laid by destroyers or large minelayers, the number being increased later as convenient. One Grand flotilla, supported by a light cruiser squadron. Two submarines as a protective screen to the South-Eastward.
Sinking plugs can be used to render the area safe to British ships after a certain interval.
XXth Flotilla can lay 494 mines in one line 18 miles long.
B – Operations with E. C. Mine Nets in the North Sea.
Enemy submarines are endeavoring to pass to the Westward of the Northern Barrage, and are believed to be following the course PQ (vido attached chart.) Grand Fleet at (a) Rosyth (b) Scapa
(a) 20 miles of mined nets to be laid at MMx flanked by hydrophone trawlers, the mined area and its approaches being continually patrolled by a flotilla of Grand Fleet destroyers.
(b) Ditto, but nets to be laid further North, in some such positions as M’M’x.
About 40 drifters for laying the nets. One destroyer flotilla, 16 trawlers, and a few kite balloons continuously on patrol.
Note: As the best results will only be obtained when a large number of submarines are on passage, and their approximate track is known, it is suggested that the various craft on the East Coast should be organized for operations of this nature, the instructions being continually kept up to date, and the material provided no matter what duty they are employed upon.
SUGGESTED PLAN FOR HUNTING BY DESTROYERS.
1. The following method of hunting is suggested for a flotilla of 13 destroyers, contact being obtained by reports from other vessles or by patrolling in line abreast along their supposed track. It should suffice if nine of the flotilla were fitted with hydrophones.
2. Assuming the visibility to be 10 miles or over, the destroyers should deploy as shown in the diagram, 10 miles apart, the center destroyer taking up a position as close to the submarine as possible. By steaming 10 miles backwards and forwards along B-D or A-C, the flotilla would cover a circle of over 50 miles diameter. If the visibility were less than 10 miles, the destroyers would have to be at visibility distance apart.
3. if the patrol remained stationary, a submarine could get from the center of the circle to the edge: -
In 3-1/2 hours at 7 knots .... batteries exhausted.
In 5 hours at 5 knots .... batteries 40% exhausted
In 12 hours at 2 knots..... batteries 20% exhausted
The hunting group would therefore have a margin of from 5 to 12 hours in which to sight or hear the submarine.
4. The procedure and station-keeping would be exceedingly simple. The flotilla, after deploying with the central destroyer over the submarine, would steer backwards and forwards, either parallel to or across its supposed track, engines being stopped to listen at pre-arranged intervals either by watch or wireless signal.
A destroyer sighting or hearing the submarine would, after confirming the fact, hoist a signal; and the whole flotilla would then alter course together so as to bring the central destroyer over the new position. At night, and when the submarine was approaching the limit of its endurance, the distance between the destroyers would be reduced.
5. It is believed that the foregoing method will succeed if submarines are once located; and judging by the experience of the Northern Patrol, the latter factor is not difficult. TEN-knot trawlers cannot be expected to destroy submarines with a surface speed of 13 to 18 knots; whilst cruiser submarines need not even dive for the trawlers and sloops of the Northern Patrol. It is suggested that a Grand Fleet flotilla be fitted and manned with hydrophones and operators taken from trawlers, and the system be tried as soon as possible.
Plans Division 27-7-18.