The first objective was realized by 1943, when the pressure firing mechanism D 1 and D 101 were completed and readied for operational use. These were used with the M 1 and A 104 units to form the combined units DM 1 and AD 104. Subsequently, the D 2 and D 102, designed to provide against actuation by nearby explosions, were developed for use in the same combination as their prototypes.

A series of uncombined pressure units, the D 103, D 113, D 123, and D 133, were de-signed for rivers or other relatively smooth waters. Only the D 103 was used operation-nally, the others were still under development at the end of the war.

A general rule prohibiting the employment of mines for which no countermeasures ex-isted prevented pressure units from being employed until after the Allied Invasion of France in 1944. The military situation by then was so grave that the Germans even laid early defective types with natural rubber bags, which allowed the air to escape in as litt-le as three weeks after the unit was underwater. This flaw, discovered only a short time before the invasion, was remedied by substitution of leakproof synthetic rubber bags.