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Admiral William S. Benson, Chief of Naval Operations, to Vice Admiral William S. Sims, Commander, United States Naval Forces Operating in European Waters

Follow up Copy

Cablegram Received August 11, 1917

Origin Opnav                  Serial No. Opnav 139

Via  N C B                    Date No. 15011

Copies to                     File No.

Action referred to:

Pay Inspector Tobey1

Opnav 139 The best listening device developed called C tube2 is being shipped to the following address period D A S D3 Admiralty London England period It is good for one mile radius all machinery stopped period extremely simple device period The twelve trawlers under officer whose signal number is 1144 and accompanying twelve submarine chasers for the French are equipped with this device 15011


Source Note: Cy, DNA, RG 45, Entry 517B.

Footnote 1: Paymaster Eugene C. Tobey.

Footnote 2: The C Tube was made from two inflatable rubber globes with low frequency receivers. The globes were towed behind a ship 5 feet apart with each globe registering sound for the operator. The accuracy of the device could locate a submarine within a quadrant up to 1000 yards away. Norman Friedman, Fighting the Great War at Sea: Strategy, Tactics and Technology (S. Yorkshire: Seaforth Publishing, 2014), 293-296.

Footnote 3: Director Anti-Submarine Division, Capt. William W. Fisher.

Footnote 4: Capt. Thomas P. Magruder.