Magnetized Charges

Clam Mk III: The clam is a small time bomb with a magnetic base, which enables it to be attached instantly to any flat iron or steel surface, such as engine blocks, railroad tracks, steel plate, etc.

The body is black plastic box with rounded corners, measuring 5¾ in. x 2¾ in. x 1½ in. At each end of the box is a magnet compartment, in which the two magnets are loosely mounted so that they can grip an uneven surface. The center compartment of the box contains about 8 oz. of the H.E. filler, usually Tetryl/TNT 45/55. The box is clos-ed by a flat lid held in place with four screws.

A standard L. Delay Switch No. 9 Mk I, with a Detonator No. 27 attached, serves as the delay initiator. It slips into a groove in the top part of the body and is held in place by a small clip.

Figure 285 – Army Magnetized Charge - Clam Mk III

Limpet Mk III: The Limpet is a small, self-contained, delay-action mine with a mag-netic base, which allows it to be fitted instantly to any iron or steel target, such as a tank or the hull of a ship.

The Limpet is designed to function either on land or under water, and carries a charge of 3½ lb. of H.E. filler, usually Tetryl/TNT 45/55, which is sufficient to pierce 60-mm plate. Exceptionally powerfull segmental magnets, flexibly mounted, allow it a firm grip even on uneven surfaces. It will remain in place on the average vessel at speeds up to 16 knots.

The explosive container of the Limpet Mk III is a separate unit, which can be detach-ed from the magnet ring so that the device can be used without magnets if desired. This container weighs about 4¼ lb. filled. The magnet ring weighs 5¼ lb., bringing the total weight of the device to 9½ lb. A carrying ring is fitted to the top of the Limpet body.

A standard L. Delay Switch No. 9 Mk I, with a Detonator No. 8 attached, serves as the dlelay initiator. It is inserted in a special holder, which gives a watertight joint when inserted in the magazine.

The earlier Limpet Mk II was fitted with two magazines, allowing the use of a dupli-cate igniter system to provide against possible failure.

Figure 286 – Army Magnetized Charge - Limpet Mk III

Rigid Limpet: The British Rigid Limpet is designed for the destruction of tanks or other steel structures. The device is painted field gray and consists of a rectangular box of sheet brass, 8¼ in. long x 2½ in. wide x 2½ in. deep.

The box contains a charge of 2.5 lb. of plastic H.E., moulded to accept a detonator at each end.

A pair of brass brackets are riveted to either side of the brass body, and a brass rod is secured between each pair of brackets. To each rod are fitted three permament U-shaped magnets, each fastened by metal straps to a rubber mounting. These magnets are retained in position by flanges on the rod. The rubber mountings allow limited move-ment to the magnets, so that the Limpet can be readily attached to uneven surfaces.

An internally threaded brass cap provides a filling hole. A threaded adapter fixed cen-trally to the brass filling cap and another threaded adapter fitted to the other end of the body provide means for inserting the A.C. Delay Igniter Mk I, with which the Limpet is fuzed.

This initiating mechanism, used only with the Rigid Limpet, is a chemical-type long-de-lay device, consisting of a brass body containing a spring-loaded striker. The head of this striker is sunk in a celluloid disc, retaining the striker under spring compression.

Immediately above the celluloid disc are located cotton wadding and a glass ampoule of solvent, accommodate in an enlarged recess in the body. The top of the body is threaded externally to receive a threaded cap. Screwed into the center of the cap is a threaded spindle, which bears on a rubber sealing disc. To the top of the spindle is atta-ched a wing bolt to permit manual operation. A safety pin pierces the threaded spindle from being screwed down as long as the pin is in place.

The device is put in operation by removing the safety pin and screwing down the threaded spindle, thus crushing the ampoule and allowing the solvent to saturate the cotton wadding and work on the celluloid disc. Eventually the celluloid is sufficiently soft-ened to release the striker, which then forced by its spring into the detonator threaded to the lower end of the body. Delay times can be varied by changing the solvent am-poule. The color of the ampoule indicates the delay at 20° C.

Dimensions and functioning details of the igniter follow:

Over-all length

Detonator length

Body diameter

Delay at 20° C

Delay times will increase at temperatures above 20° C, and decrease if temperatures are below that point.

Figure 286 – Army Magnetized Charge - Rigid Limpet and Igniter