Naval History and Heritage Command

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

NAVY DEPARTMENT

BUREAU OF ORDNANCE

33-452 (Q1) -0 FF       Washington, D.C.

CONFIDENTIAL.                                   March 4, 1918.

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

SUBJECT:  Depth Charge policy.

Reference:  (a) Vice Admiral’s letter Jan. 7th – same subject.1

     1.   The Bureau has been furnished a copy of the Vice Admiral’s letter, reference (a). The Bureau is thoroughly in accord with the Force Commander’s suggestion that a large number of depth charges should be carried for the anti-submarine campaign and is prepared to furnish depth charges in large quantities upon the request of the Force Commander.

     2.   The Bureau notes in paragraph 3 of reference (a) several dangers which the Force Commander calls attention to. These dangers are stated as applying to both British and U.S. depth charges. Quoting from reference (a):

“The principal dangers are:

     “(a) explosion by shock from gun blast.

     “(b) explosion at low speeds due to being knocked overboard by collision, torpedo or mine damage, or accident.

     “(c) premature explosion of one charge by that of another dropped within 100 feet, and

     “(d) explosion by direct gun hits.”

     3.   The Bureau invites attention to the essential differences between the British and U.S. depth charges, and supplies for the information of the Force Commander, the results of tests, made subsequent to the receipt of the Force Commander’s letter, to demonstrate the susceptibility of the U.S. depth charges to the above noted dangers.

     4.   The sensitiveness to shock, gun fire and countermining of the British depth charge is largely due, excluding the firing mechanism, to

          (1) Detonator housed in primer and not in safety position.

          (2) Primer is of dry gun cotton.

The U.S. depth charge has the primer withdrawn in a safety position until the depth charge has sunk a minimum of 20 ft. The Primer is of T.N.T., much less sensitive than dry gun cotton.

     5.   The following tests have been carried out.

(a)  Susceptibility to explosion by shock from gun blast. Depth charges placed horizontally and also vertically have been placed under the muzzle and at various distances beyond the muzzle of a 4ʺ gun, fired at 0° elevation, with full service velocity – distance from line of fire to centre of depth charge, 30ʺ. Safety fork off. In no case was the depth charge exploded nor the detonator fired, nor the firing gear functioned, nor the extender mechanism functioned or damaged.

          The U.S. depth charge is therefore considered safe against explosion by shock from gun blast.

          (<b>)Explosion at low speeds on being knocked overboard. The United States depth charge is subject to this danger. With the new launching gear to be installed on new destroyers, it is anticipated that it will be impossible to arm the depth charges by accident, collision or other cause, except deliberate and intended dropping. For the moment, however, it is recognized that this danger exists.

          (c)  Premature explosion by countermining. A depth charge was fired at a depth of 50 ft., and distant respectively 50, 100 and 150 ft., from depth charges suspended at a depth of 50 and set for 100 ft. None of the other depth charges exploded. It is concluded that the U.S. depth charge will not countermine.

          (d)  Explosion by direct gun hits. Depth charges were exposed to the following firing tests:

          (1)  3” Common shell black powder striking depth

                 charge and exploding.

          (2)  3” High Explosive Shell striking raft at a

   distance of 2 ft., from depth charge and

   fragments penetrating depth charge.

          (3)  3” High Explosive Shell striking depth charge and

                 exploding therein.

          In all the above cases the detonator was exploded but in no case was the depth charge itself exploded, although torn apart by the explosion of the shell.

     6.   In view of the above the Bureau suggests and strongly recommends, the following:

          (A)  United States vessels to use United States depth

              charges only.

          (B)  Revision of paragraph 4 of reference (a), to permit uninterrupted and

    unrestricted arc of fire to guns, and to retain depth charges on board in case     of impending gun action.

Ralph Earle.