Arming Clocks. As a necessary accessory to the first influence mine units, the Ger-man Navy designed a six-day arming clock, the UES I. The primary purpose of the arming clock was to allow influence mines of the ground type to settle securely in the bottom prior to arming. Secondarily, it was used to hinder sweeping operations. The range of the clock was from one-half hour to six days, and the settings were always for the maximum period consistent with the military objective. Various improvements were made both prior to and during the course of the war, but basic operation was never altered.

Late in the war the German Navy introduced a new type or arming clock, the ZE III. This clock could be set from five to two hundred days, and could be utilized either for arming of for disarming. A similar 360-day clock, also known as the ZE III, was under de-velopment at the close of the war. The only other delaying arming clock used was an eighty-hour type employed with the BM 1000 mines to permit proper orientation of the case prior to arming.

Period Delay Mechanisms. Another important series of clockwork mechanisms used in German mines were the Period Delay Mechanisms ZK I, ZK II and ZK IIa through ZK IIf. The mechanisms were so designed that from one to eighty-five actuations within pre-scribed time periods were necessaey to fire the mine. The first of the mechanisms, which possessed a span of only six actuations, was intended to defeat the practice of having minesweepers safeguard outgoing vessels by precoding their passage from port. The last model, the ZK IIf, which could be set up to eighty-five, was designed to make clearance sweeping extremely burdensome.

Sterilizers. The third large group of clockwork mechanisms consisted on seven diffe-rent types of sterilizers, with maximum time periods as follows: ZE (80 days), ZE I (80 days), ZE II (6 days), ZE III (200 days), ZE III (360 days), ZE IV (45 days) and ZE IVa (60 days). In addition, a 200-day electrolytic cadmium cell sterilizer was developed. All the sterilizers were used in various German mines to limit the life of minefields in accord-ance with tactical requirements. They were widely used to permit the replenishment of E-boat laid minefields off the English coast.

Pausenuhr. Several clockwork mechanims served special purposes. The most import-ant was an 18-day clock, the Pausenuhr, which armed and disarmed a mine once in every 24 hours. The German Navy developed this clock after it observed that the British normally made morning sweeps after minelaying sorties and allowed traffic to resume by midday.

Twelve-Hour EW. Another clock, the twelve-hour EW, was used with the M 3 unit in moored influence mines. The EW tested the mine circuit for a period of up to twelve hours after laying, and scuttled the mine at the end of the set period if it planted impro-perly or was otherwise disturbed.

Prevent-Stripping Mechanisms. To protect influence mines from capture, the Ger-mans devised a variety of mechanisms commonly reffered to as "booby-traps" or "Pre-vent- Stripping Mechanisms". They consisted of specially designed bomb fuzes to explode aircraft mines that fell on shore, photoelectric cells which fired the mine if it were expos-ed to light by the removal of the unit dome, sea cells to explode the mine if the unit was exposed to moisture, a variety of anti-withdrawal and anti-removal devices, and a unit to fire the mine if it were moved into shallow water or inadvertently laid in tidal flats. These devices were used widely in the early phases of the war. However, after several accidents involving the loss of German mining personnel, they fell into disfavor. During the latter part of the way they were used infrequently.

Räumschutz. When the German acquired complete information on Allied magnetic sweeping procedure through the capture of a BYMS off Leros, they undertook develop-ment of Räumschutz (area protection) to defeat the LL-type sweep. These units, for use with the M 1, MA 1 and MA 1a mines, were to be designated M 1r, MA 14 and MA 1ar. They were in production in 1945.

Räumschutz was a rubber-covered cable 165 feet in length with one copper electrode secured to the end and another mounted on, but insulated from, the mine case. In ope-ration, the sea current produced by an LL-type sweep was picked up by the electrodes and, through a sensitive relay, the mine was rendered passive for the duration of the sea current plus a predetermined period. According to reports, the Germans attempted to fit Räumschutz to aircraft-laid mines using the MA 105 unit. However, considering the na-ture of the device, probably the inherent mechanical difficulties were insurmountable.