MA 1st. MA 1st is a further modification of MA 1. The modification did not reach the operational stage and was being tested at the end of the war in Europe. It consists essentially, of the substitution of a "stumpf" (coarse) microphone in the circuit, making the overall system very insensitive and suitable as an anti-mine-sweeper unit.

The ZK II mechanism is used in this unit. The ZK IIe mechanism has a cam-operated switch which is closed for 15 seconds after a magnetic actuation and then open for 120 seconds in parallel with another cam-operated switch which is closed only after 84 cyc-les of the mechanism. Through this system, acoustic actuation must take place within 15 seconds after triggering or result in triggering only with an interval of 120 seconds, for a maximum of 84 times. After the 84th cycle, the circuit is made normal. This system would require that a mine-sweeper make sufficient acoustic influence on the mine within 15 se-conds after magnetic triggering to fire the unit when fitted the "stumpf" system.

Figure 200 – MA 1, MA 1a, MA 1st Circuit