Vice Admiral William S. Sims, Commander, United States Naval Forces Operating in European Waters, to All Naval Forces in European Waters
U.S.NAVAL FORCES OPERATING IN EUROPEAN WATERS,
U.S.S. MELVILLE, Flagship,
August 19, 1918.
CIRCULAR LETTER NO. 79.
From: Force Commander. SECRET
To : All Forces.
Subject: Information concerning enemy submarine tactics.
1. The following is for your information:-
From survivors of a “U” boat, it has been ascertained that during their daily practice dive at sea, when weather permitted; the crews were usually exercised for an hour in depth-keeping with the boat proceeding at one knot. In this boat the procedure for silent running was as follows:-
Usually at dead slow speed, 1.9 knots; port motor stopped and starboard motor making 100 revolutions per minute.
When required, slow speed, 3.2 knots; port motor making 95 revolutions and starboard motor 100 revolutions per minute.
When higher speed was necessary, at half speed, 5.2 knots, port motor making 150 revolutions and starboard motor 190 revolutions per minute.
The forward hydroplane and steering gear were clutched into hand by means of the quick change over arrangement described in C.B. 01444 o.x.o. page 9, and the depth keeping was done with the after hydroplanes, which were left in power. Even when in hand the hydroplanes and steering gear were said to be noisy.
Trimming was done by means of compressed air. This means no pumps were used when running silently.
2. It is apparent from the above that, on many occasions when a vessel fitted with listening devices has unaccountably lost sound, the submarine may have resorted to silent running. On such occasions the search must not be abandoned but, some move other than merely continuing to listen in the spot last heard should be made. For example: running a retiring search curve, based on estimated silent speed; listening at frequent intervals, combined with use of trailing wire; or judicious use of depth charges with an idea of frightening him into a more audible speed. The particular plan to be adopted, will depend on the circumstances of the individual case.
3. Do not give up search until every possible scheme has been tried.
Source Note: Cy, DNA, RG 45, Entry 517B. Addressed below close: “Copies to:/Brest 150/Gibraltar 35/MELVILLE
75/Aviation (Capt. [Hutchinson I.] Cone) 30/Azores 15; N.P.O.Plymouth 1/Captain [Richard H.] Jackson 2; [Joseph Strauss
] Commander Mine Force 32/Sixth Battle Squadron 13/C.O.Receiving Ship Liverpool 2/Base 25 [Corfu, Greece], 45; N.P.O.Cardiff 1/[Adm. Henry T. Mayo
] C-in-C Atlantic Fleet 1/ [Frank McRary
] Commander Air Stations in Ireland 12/Commanding Officer, Base Hospital Two 2/C.O. U.S.Naval Base, Plymouth 45/Naval Attaches: [Charles R. Train
] Rome, [Richard H. Jackson] Paris, [Walter S. Crosley] Madrid, [Lt. Col. Arthur T. Marix, U.S.M.C.] Christiania,/ [LyndeD. McCormick] The Hague, [John A. Gade
] Copenhagen, 1 each./Bunav 2; Bunav for New Destroyers 50/Cmdr. Roger Williams
, Gen.Hdqs.Am.Exp.Fcs. France 2/C.O.U.S.N. Avi. Det. R.A.F. Killingholme 1/Commander Sub Chaser Detachment 3, 40,/Files 175.”