The EMK and EMU Mines. The development of the EMK was undertaken in 1940, the mine being intended for use as a moored contact and/or influence-type mine. In 1944 its development, which was still incomplete, was discontinued in favor of the smaller EMU. Since the EMK and EMU were identical, except for size (EMK 44 inches in diameter and EMU 40 inches), they are discussed together in the following paragraphs.

The EMK was dropped in 1944 in favor of the EMU because of a shortage of explosive. (The EMK was designed for a charge of 660 lb., the EMU for 220 lb.) Since these mines were radical departure from previous German types (Figures 22, 23), their development progressed slowly. Consequently at the end of the war neither the EMK nor its succes-sor, the EMU, was completed.

By 1940 the Germans had realized that their standard-type base plates for moored mines had two serious shortcomings:

1. In deep water, hydrostatic pressure sometimes prevented arming by counterbalan-cing the pull of the mooring cable.

2. In shallow water, rough seas caused excessive arming and disarming, and frequent-ly wore out the spindle-mechanism membrane.

To cure these defects an entirely new type of base plate was designed. (Figure 22). This base plate utilized an inverted spindle action, so that water pressure and mooring-cable tension combined to arm the mine. In depths over 30 feet, hydrostatic pressure alone would maintain the mine in an armed position, regardless of vertical motion of the mine case. In water depths of less than 30 feet, disarming due to vertical motion of the case was prevented by a dash-pot mechanism which maintained arming of the mine for 60 seconds after release of tension, on the mooring spindle.

The method of placing the main charge in the EMK and EMU differs from normal Ger-man practice. Whereas all other German moored mines employ a charge container, the EMK and EMU were designed to house the charge on the bottom of the mine case. The German felt that loading the mines in this manner would give the mine a greater lethal range and permit better mine orientation.

The anchor of the EMK and EMU mines was also of new design. Its most noteworthy feature was the fact that it was so designed as to permit depth setting either by plum-met or by hydrostat (Figure 23). The plummet-line drum was designed to accommodate 100 feet of 3/16-inch cable, and the mooring-cable drum 500 feet of 7/16-inch cable. An 18 - 30-foot length of chain was to be used between mooring spindle and mooring cable. Because of its departure from previous German types, the development of this anchor progressed slowly and was not completed at the end of the war.

Figure 22 – EMU Mine

Figure 23 – EMU Mine and Anchor