The MA 105 unit is a further Luftwaffe development of the MA 101 unit. Although many samples of MA 105 were captured in the Mediterranean area in 1943, it is not de-finitely known to have been used operationally. The magnetic component is a new bi-polar magnetic needle device capable of repeated resetting to assure proper latitude ad-justment and to accommodate small changes in the prevailling magnetic field. It is similar in operation to the M 4 unit developed by SVK embodying the usual Luftwaffe magnetic-unit construction. The acoustic component is a new type which uses two pentode ampli-fication stages.

The MA 105 unit is a combined magnetic-acoustic mine firing mechanism of the same basic design and appearance as the obsolete MA 101 (Allied designation AM Mk II) with several improvements. However, the unit uses the same type of microphones (four in number) as the MA 101 unit. The microphone is very insensitive and decreases in sensi-tivity with the depth of water. Final investigation may shwon unique characteristics of the acoustic component, but preliminary examination of the available information tends to indicate that the magnetic component is the primary firing device with the acoustic component introduced to make sweeping more difficult. The MA 105 unit is designed for laying in the BM 1000 H mine. There is some evidence to indicate the existence of an MA 105r unit ("r" equals raumschutz). It is not known how the "raumschutz" anti-sweep-ing device could be handled in the laying of a bomb-mine.