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Rear Admiral Ralph Earle, Chief of the Bureau of Ordnance, to Vice Admiral William S. Sims, Commander, United States Naval Forces Operating in European Waters



Sept 7, 1918  

To  :     Vice Admiral Commanding, U.S. Forces in European Waters.

Subject :  Ordnance inventions – Planning Section Memo, #41 – Anti-submarine tactics.

Reference :    (a) Force Comdr’s letter 29262 Aug 14.1

     I.   The Bureau notes the developments suggested as urgently needed for use in the anti-submarine campaign in Planning Section Memorandum #41.

     2.   The majority of these suggestions had been anticipated by the Bureau and experimentation on the development of the devices noted undertaken. Progress is reported as follows :

(a) Marker shell – A shell filled with oil to form a slick upon the water can be supplied at once. The more complex form of shell to give a light and smoke on the surface of the water is under experimentation.

(b) Flexible Depth Charge Thrower – A single barrel depth charge thrower, capable of train is under development. No variation of range other than the use of varying powder charges is contemplated with this type.

(c) Non-secret Mine – The Bureau can produce the Mark IV Contact Mine at call. A hirn mine2 is being designed. Despite the advisability of retaining secrecy in connection with the Mark VI Mine, the Bureau has not been able to conceive of any practicable method for the enemy to nullify the action of this mine, even should its principle become known to him.

(d) Torpedo Firing Mechanism sensitive to a vessel within 70 ft. Preliminary investigations are under way concerning the possibility of a hydrophone controlled torpedo, by which the torpedo will be steered to the source of the sound. This promises considerable difficulty although of great value if achieved. The investigation of the applicability of a magnetic mine firing device to a torpedo has been commenced but no conclusions as to the feasibility thereof have been arrived at

(e) Mine Firing Mechanism, sensitive to a vessel within 100 ft. of the mine. Magnetic Mine Firing Mechanism suitable for ground mine has beendeveloped. Investigation to apply this mechanism to an anchored mine or suspended mine, so that it will be proof against firing by oscillations produced by water movements, is under way.

/s/ Ralph Earle.

Source Note: Cy, DNA, RG 45, Entry 520. Document identifier in upper left-hand corner with note: “In reply refer to :/32934/ 99 – (QI) -0/FF”; and in upper right-hand corner”3/J.”

Footnote 1: See: Sims to Base, Detachment, Squadron, and Division Commanders, and Certain Ship Commanders, 15 August 1918. The Planning Section report is incorporated in that document.

Footnote 2: Presumably, Earle meant horn mine. For a picture of a German WWI horn mine, see: Illustrations for September 1918.

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