Because of some operational shortcomings the AT 2 (AA 2) and AT 3 (AA 3) units were considered unsatisfactory. Combination of these units with the M 4 unit was in de-velopment at the end of the war in Europe. The resultant combinations are known as AMT 1 and AMT 2 (Aocustic-Magnetic-Subsonic). No samples of the AMT units were captured.

The operational AT units had two faults:

1. Both AT 2 and AT 3 tend to detonate spontaneously in strong currents.

2. Because of constant switching in the vicinity of a sound source, the life of the AT units is short, especially AT 2. (50 hours for AT 2 - 14 days for AT 3).

Combination of AT 2 and AT 3 with M 4 into AMT 1 and AMT 2, respectively, is desig-ned to overcome these two faults and, in addition, make the mine more difficult to sweep. Combination is made with the use of a ZR II motor-driven cam system to set the time interval relations between the three influence components of the unit.