The M 1 (Allied Designation M Mk II) unit falls into a general class of early magnetic firing devices known as BIK. BIK is an abbrevation of the OKM designation of the device which is "Ballon Inklinatorium", and is a cover name for all firing devices coming under this heading. Later, experiments with these units became mor specialized to adapt them to special purposes, and separate designations were applied to the different variations. The modificatons described herein are developmental modifications, some of which were on the verge of becoming operational.