Part of the German mine-development program was directed to work on supersonic fired mines. At the end of the war in Europe four supersonic units were under develop-ment, and of these, the (AA 4) had been abandoned. The units were designated AE 1, AA 4, AE 101 and AA 106. Of these, the AE 1 and AA 4, AA 101 are active ("pinging") supersonic units.

The German AA 4 and AA 106 are directional supersonic mine firing units. Because of the directional requirements, self-orienting properties are necessary to the directional elements. At first, SVK attempted to mount a group of directional magneto-strictive re-ceivers (seven in number) in a belt around an LMB mine case. The topmost receiver was selected for operation by a weighted internal pendulum switch. This was unsuccessful. In the case of the AA 4, which was designed for use in the EMF and SMA mines, the direc-tional elements were mounted in the cover-plate and since the mine-case is self-orient-ing, no additional provision was necessary for vertical orientation. In the case of the AA 106 (sometimes reffered to as A 106), the unit is designed for use in the BM 1000 H and BM 1000 L ground mines. When used in ground mine, the directional elements are mounted in a small float which is moored on a two-/three-foot length cable from the mine. The float is released shortly after the mine reaches the bottom. The supersonic system is switched on, to save battery power, by a simple sonic-acoustic system of low power consumption. The supersonic receivers were designed to fire when the target was nearly overhead and to discriminate against ships passing abeam.