Vice Admiral William S. Sims, Commander, United States Naval Forces Operating in European Waters, to Rear Admiral Henry B. Wilson, Commander, United States Naval Forces Based in France
Troop Transport, Special Letters.
3 August 1918.
From: Force Commander.
To: Commander, U.S.Naval Forces in France.
Subject: Sailing U.S.S. LEVIATHAN in Convoy.
1. Since the operation of cruiser submarines in the Western Atlantic, the Navy Department has been considerably concerned regarding the safety of all loaded troop transports in the Western Atlantic. In order to reduce independent sailings and so minimize the chances of encountering a submarine, the Department has decided to sail the LEVIATHAN with the GREAT NORTHERN and NORTHERN PACIFIC on the flanks.
2. I pointed out to the Department that, so far as concerns the European zone, I consider the LEVIATHAN safer when sailed alone under an escort of four or more destroyers than when sailed in convoy. We have had a great deal of experience in escorting vessels singly, and when fast vessels are adequately escorted the chances of coming safely through submarine waters are, in my opinion, considerably greater than when in convoy unless a very strong escort is available for the convoy. There are repeated cases of submarines attacking strongly escorted convoys, but we have had practically no losses when fast vessels are escorted singly. Furthermore, sailing the LEVIATHAN singly makes a smaller and more uniform demand on destroyer escorts, - a very important point in economizing destroyers.
3. Convoys were established not to add additional protection to ships, but as the only means possible of economizing destroyers. Submarines have become used to convoys, and undoubtedly most of them have had some experience in attacking convoys. A fast ship zigzagging and closely guarded by x four destroyers with possibly a distant patrol as well is a very disagr<e>eable looking target for a submarine, and experience has shown thus far that submarines are not anxious to deliver an attack under such conditions.
4. The present disposition of escorts for convoys tends to ensure maximum protection around the flanks and ahead, with weaker protection or none at all astern. Undoubtedly this arrangement of escort protects the most vulnerable parts of the convoy, but submarines have noted the weak protection astern and frequently submerge ahead of a convoy and deliver a quarter shot between the columns or from astern after the convoy has passed. In this position a submarine is in least danger of attack by escort, and he has a favorable position for delivering an effective shot, particularly if the convoy happens to zig-zag conveniently and exposes a large area of target. The quarter shot is very usual with submarines, particularly with submarines recently commissioned, not only in attacking convoys but in attacking single ships as well, for in delivering a quarter shot the submarine is not exposed to any danger of being rammed, and as the escort is usually very weak or absent astern an excellent opportunity is given of bringing off a favorable shot with minimum risk to the submarine. The plan followed by the submarine is to submerge ahead of the convoy and at right angles to its course, so that the hydrophones on one side are effective. When the opposite hydrophones become effective the submarine is certain that the convoy has passed his position and he can shortly thereafter emerge with certainty that the convoy has passed beyond him. If he has attained submerged a good position (and his hydrophones assist him in this) he may be in excellent position for an effective quarter shot. The JUSTICIA, PRESIDENT LINCOLN, COVINGTON, TUSCANIA, ANTILLES, TIPPECANOE and many others have been sunk by quarter shots. With fast convoys there is no doubt that a quarter shot is the usual one.
5. Whenever the LEVIATHAN is sailed in convoy it is directed that in addition to the usual screening particular care be tkaen to place a part of the escort in such position as to guard against the chance of a submarine making a close quarter shot against the LEVIATHAN. This matter of quarter shots should be carefully considered in disposing the escort for all convoys.