Vice Admiral William S. Sims, Commander, United States Naval Forces Operating in European Waters to Secretary of the Navy Josephus Daniels
Letter No. 1.
Office Vice-Admiral, Commanding
U.S. Destroyer Forces
London, 13 June 1917
From:- Vice-Admiral Wm. S. Sims.
To:- The Secretary of the Navy (Operations).
Subject:- Convoy operations in submarine danger zone.
Reference:- Department’s Cable 21009.
1. With reference to the Department’s cable, 21009, concerning methods of protecting future convoys of troops or supplies for our army and navy forces while in submarine danger zone.
2. The governing considerations in the question of escorting through the submarine zone are:-
(1) Latest information concerning enemy activity.
(2) The question of not entirely abandoning our own offensive campaign in favor of escorting duty, and
(3) The question of the number of craft available for such duty and thier disposition.
If, for example, enemy activity is concentrated to the westward of Ireland and convoys are coming in well to the southward of this area, it manifestly is important to concentrate our offensive campaign in the area in which the enemy can be most effectively attacked.
In deciding as to the number or types of ships to be diverted from offensive operations preference is always given, of course, to convoys carrying troops. Convoys carrying material, whether it be munitions, animals or food supplies are escorted whenever necessary; but such escorting duty is not allowed materially to interfere with the offensive campaign in operation at the time in question.
3. In those areas which are constantly being covered by destroyers or other anti-submarine craft, such as sloops, (specially built anti-submarine vessels, about 1200 tons) the attempt is made to avoid taking such vessels out of their designated patrol squares. The vessel, or vessels, which first picks up a valuable cargo escorts it through her square, notifying the patrol vessel on the next square inshore, and turning over to her as soon as the meeting of the ships is effected. If by reason of thick weather, etc., contact is not made the convoying vessel continues on to the next square.
4. The routes which will be followed by our troop and supply ships bound for France are, generally speaking, outside of the main areas of submarine activity, and hence outside of the areas continuously patrolled by destroyers and other anti-submarine craft, except for a short distance off the west coast of France.
5. For the purpose of handling such convoys, and also the merchant shipping convoys which are now in operation from Hampton Roads to the Mediterranean, the Admiralty have established, for convenience in their own administration, a comparatively large number of rendezvous, well out to sea, and encircling the British Isles and west coast of France. Also a comparatively large number of locations on the Irish, English and French coasts have been given designating figures or symbols. It will therefore be the practice each time that one of their convoys sails from a foreign port, to designate a rendezvous which they are to pass through, and a point on the coast which they should steer for after passing through the rendezvous.
This requires a notification well in advance, giving as closely as possible the time that convoys will pass through the rendezvous points designated. Escorting destroyers will then be able to intercept the convoys at some point on the route between the rendezvous and the point designated on the coast, the position of interception dependent primarily upon enemy activities at the time. It manifestly must also be possible to communicate in cypher with convoys at sea and divert them from one rendezvous to another, if occasion demands.
The above-mentioned lettering and number of rendezvous and points on the coast are, as stated, primarily for convenience of reference in administration in the Admiralty itself.
The significance of such symbols if circulated even to our own Allied officers abroad must necessarily be limited to the maximum extent in order to preclude any possibility of enemy becoming aware of them.
6. If the greatest possible degree of safety for convoys is to be insured it is entirely necessary that their movement should be under control of one source, and therefore as all enemy activity is concentrated on this side of the Atlantic, and his main effort must necessarily remain in its present zone, it follows that selection of rendezvous routes and other directions in regard to movements of convoys should be controlled and directed from this side, that is, in the Admiralty itself. It is for this reason that the Admiralty has requested, and I strongly recommend, the immediate detail of a competent and tactical officer whose duties in the Admiralty under my general direction will be confined to those above indicated.
7. The following procedure in regard to convoys is therefore recommended:–
(1) Early advance information regarding perspective sailing of convoys and their character.
(2) Immediate information as soon as definite hours of sailings can be foreseen.
As soon as this information is received, and after consultation with the Admiralty, a rendezvous and route to be included in the sailing orders will be selected and given. Definite information should then be given when convoy sails, as to its prospective speed and time of passing through rendezvous designated.
8. It is urgently requested that only British Admiralty codes be used for such communication, addressed to the Admiralty, the first word of the message being “Sims.”
9. Under no circumstances, if convoys are divided into groups, should these groups use the same rendezvous in the same route after reaching the danger zone, as in such a case if the enemy should become aware of their movements he would be able to concentrate for successive attacks.
10. Ships of convoy should zigzag together from two to four points irregularly. Organized irregularity is one of the principal requirements in opposing submarine attack.
11. Escorting destroyers should be allowed the maximum independence of movement and exercise of ini[ti]ative. They should not be held to strict formations in reference to bearings and distances from the convoy. This procedure is necessary in order that full advantage may be taken of their experience in operating against submarines and their later information in regard to enemy methods, which are continually changing.
12. It is mandatory that the wireless should be used as little as possible. In fact, it would be better not to use it at all, except for important directions which may have to be sent from shore as to changes of routes. Evidence indicates that the enemy has been successful in the use of radio direction finders, particularly in locating large forces or radio work of an unusual or distinctive character.
13. It is apparent that once a convoy enters the danger zone an escorting cruiser is of little or no protection against submarines, and virtually becomes one of the convoy itself, also requiring protection.
14. Up to April 1st, there is no evidence to indicate that any German submarine carried beam tubes, and this is one of the principal reasons why they have never attempted attacking a formation from ahead, that is, approaching from ahead and firing as they pass through the formation. With bow tubes they would be forced to use the helm before reaching the formation, with considerable danger to themselves, which they seldom if ever incur. Hence the principal arc for destroyer protection is on the bows and wings of formations.
15. The two principal requirements of formations of a considerable number of ships for defensive purposes against submarines, are: –
(1) Minimum depth of formation, – that is minimum length of formation in the direction of course. This in order to reduce the arcs on the bows and beams, which must be protected by destroyers.
(2) The second consideration is to concentrate the formation as much as possible, – that is, it is also necessary to reduce the dimension of the formation at right angles to the course.
This not only reduces the range of visibility of the force, but also restricts the advantageous positions of attack which the submarine desires to attain.
It is for the above reasons that line of divisions formation is generally adopted, with the distance between columns as small as consistent with zigzagging and evolutions.
W. S. Sims