To thwart British countermeasures and give greater life and sensitivity to units, the German Navy developed a series consisting of a combination of two or more firing mecha-nisms, each which operated on a different principle. The earliest of these, the MA 1, built in 1941, combined the M 1 magnetic and A 1 acoustic units. Improved versions known as the MA 1a, MA 2 and MA 3 followed. The Luftwaffe made a similar combination, the MA 101, with improvements designated MA 102 and MA 105.

In 1942 the pressure-magmetic DM 1 vent into production; the following year, the pressure-acousitcal AD 104. These early pressure combination were followed by the DA 102 pressure-acoustical series of sevene different units. Of these, only the DA 102 was used operationally.

Another important series of combined units, the double acoustic, utilized a sonic acoustic system for triggering the subsonic or supersonic system. These units were known as the AT 1, AT 2, AT 3 and AA 106 (All subsonic) and the AE 1 and AE 101 (both supersonic).

By May 1945, three-unit combinations were reaching the operational stage. They consisted of the MDA 106 (Magnetic-pressure-acoustic), JDA 105 (induction-pressure-acoustic) and the ATM 1 and 2 (acoustic-magnetic-subsonic). Two miscellaneous combi-ned units which never reached an operational stage were the DS 1 (pressure-seismik) and the JD 2 (induction-pressure).