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Vice Admiral William S. Sims, Commander, United States Naval Forces Operating in European Waters to Commanding Officers, Sub-Chasers and Destroyers



U.S.S. MELVILLE, Flagship.

London,   England.

22 August 1918.


From:     Force Commander

To:       Commanding Officers, Sub-Chasers and Destroyers.

Subject:  Extracts from Admiralty C.M.O’s1 August 1918 re submarine hunting.

The following extracts from British Admiralty Confidential Monthly Orders for August 1918 is quoted for information and guidance :-

     “1.  Submarine Sighted by Surface Craft - Action to be taken.

1.   From numerous instances which constantly occur of attacks on our submarines by our own surface craft - particularly by A.P. Vessels2 - it is evident that there is considerable “confusion of thought” as to the action to be taken, and while realizing the necessity of instant action against a reasonably probable ENEMY submarine under all circumstances, it is considered most necessary to safeguard our own submarines as far as possible from hostile action by a friendly vessel, especially in view of the increased severity of depth charge attacks.

     It is with this object that the following guiding principles are set forth :-

          2.   General Rules for Surface Craft.

          (a)  All periscopes are to be treated as hostile, except as stated in paragraph 4.

          (b)  Whenever a submarine in diving condition (i.e. no one on deck, mast down) is sighted, she is to be treated as an enemy unless one of the correct Identification Signals is made. The current Key Memorandum No.33 gives full details

              (1)  How to challenge a submarine

              (2)  How a submarine establishes her identity.

          3.   If a submarine comes to the surface and makes any signal, or if men come on deck and she shows no sign of diving, opening fire or running away, this may be taken as prima facie4 evidence that the submarine is either friendly or damaged. In either case surface craft should close the submarine and challenge but take no further action so long as the latter makes no effort to dive, open fire, or run away, or fails to reply to the challenge.

              There is nothing to be gained by opening fire at long ranges on a submarine which is making no effort to get away; the chances are that she is friendly, also that the shots will fall nowhere near her; even if she eventually proves to be a disabled enemy submarine, the surface craft has appreciably improved her position by closing. Hostile action therefore should not be taken against a submarine at long range unless she attempts to dive, open fire, or run away.

          4.   Surface Patrol vessels patrolling in the vicinity of the patrol lines are to be informed of the positions of the patrol lines occupied by British and U.S. submarines. Periscopes are not to be attacked in the immediate vicinity of these lines unless a submarine has recently committed some definitely hostile act in that position.

     2.   Damaging Submarines on the Surface by Ship’s Gunfire.

          1.   The structure of German Submarines is such that the best hope of inflicting fatal damage by gunfire from ships is to obtain a hit ON THE WATERLINE.

          2.   The higher up the hull the projectile hits the less chance is there of fatally injuring the submarine.”


Source Note: Cy, DNA, RG45, Entry 517B. Distribution list below close: “Copies to: Brest 150/MELVILLE 75,/Gibraltar 35,/Azores 15,/C-in-C Atlantic Fleet 1[Henry T. Mayo]/ Sub Chaser Detachment One 60/ Sub Chaser Detachment Two 40/Files 175.”

Footnote 1: That is, Confidential Monthly Orders.

Footnote 2: That is, armed patrol vessels.

Footnote 3: Document not found.

Footnote 4: That is, based on the first impression.

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