When the German launched their research for a magnetic mine unit, they simultane-ously undertook the development of a mine case to house it. The earliest of those cases were the RMA and RMB ground mines, both of which were hemispherical in shape, of all-aluminum construction, and designed for laying by surface vessels. The hemispherical design was to insure proper orientation of the magnetic unit after planting. When experi-mentation showed that the case tended to sled on laying, a specially designed float was added to the mine. The purpose of the float was similar to that of a drogue, i.e. to slow the descent of the mine in water and to prevent sledding and tumbling.

During the war, additional mines of the RM series were developed. This series consist-ed of surface-laid ground mines which could be utilized as influence and/or controlled mines. These were the RMD, RME, and RMH. The RMD could be fitted with any of the va-rious firing units; the RME was for use in rivers with an M 1 unit; and the RMH was a wooden-box sea mine of simple design which also housed an M 1 unit. This RMH was in-tended for local fabrication, so that overtaxed transportation facilities could be partially relieved from carrying bulky and heavy mine cases over long distances.

After completing the RMA and RMB, the Germans sought to exploit the potential value of influence mines that could be laid by aircraft. Accordingly, they developed the para-chute mines LMA and LMB. These were ground mines, cylindrical in shape and of all-alu-minum construction. They were used very widely during the war, with satisfactory re-sults except for one important factor: the maximum laying speeds and altitudes were too low. This led the Luftwaffe to push the perfection of a high-altitude, high-speed mine that would provide greater safety for the laying aircraft. The answer found was the Bomb-Mine 1000, which is discussed in later paragraphs.

The LMA and LMB received serveral interesting wartime modifications. When British airpower and antiaircraft fire made aircraft mining extremely hazardous, the mine were changed to that they could be layd by E-Boats, and redesignated LMA/S and LMB/S. They differed from the air types only in the type of tail used and the elimination of the bomb fuze. A further innovation in all these mines was the substitution of pressed paper (Preßstoff) for aluminum in the fabrication of the mine case, in order to reduce the high cost and fo forestall any future aluminum shortage. It was difficult to keep these types, the LMA/F and LMB/F, watertight, but, as they were found stored at operational airfields in France and Belgium, they were in use or ready for use.

The LMA and LMB mines presented an additional problem. Since they were of the ground influence type they could not be employed in depths of up to 1,000 feet. Later a modified LMF, the LMF/S was introduced for laying by E-Boats.

The Luftwaffe, being unsatisfied with the  LM mines because they necessitated low-altitude drops at low speeds, pushed the development of their cylindrical, manganese steel bomb-mines, the BM 1000 series. By 1945 they had developed mines that they could drop from heights of up to 21,000 feet at speeds of over 400 m.p.h. This was achieved by the use of break-away flat nose, small parachute, and other accessories. Of thirteen different types of bomb-mines, five were used operationally. One, the BM 1000t, was a moored mine intended to attain the same results as the LMF. However, this mine proved unsatisfactory during dropping tests and was abandoned in 1944.

To round out their influence mine program, the German developed a variety of ground and moored types for laying from submarines. The earliest were those which could be laid from submarine torpedo tubes, the TMA (moored) and the TMB (ground). In 1939 the TMC, a larger version of the TMB, was developed to meet field requests for a submarine-laid mine with a heavy charge. TMC housed over 2,000 lb. of hexanite.

When these mines had been completed, the development of a mine torpedo (MTA) was undertaken. This project was successfully completed by 1942, and mines of this type were used operationally during the war. The mine was intended for use in harbors, to be laid by being fired from submarines standing off shore. The advantages were that it reduced the risk of detection by harbor defences and permitted safe replenishment of fields already laid.

The other series of submarine-laid mines were all of the moored type for laying from the vertical shafts of special minelaying submarines. The first of this series was the SMA, which was laid off the America in fields off Halifax and Panama in 1942-1943. In 1943 a clock was added to the SMA anchor to obtain a delay of up to 60 days in seperation of mines and anchor. This modified assembly was called the SMC. The development of an additional type of SM mine, the SMB, was undertaken prior to the war but never progres-sed beyond the preliminary design stage because of the low priority assigned to the pro-ject. This mine was intended for use in depths of up to 9,000 feet, especially off the American coasts.

Simultaneously with the development of the TM mine series, the German Navy perfec-ted a moored influence case for surface laying, the EMF. This assembly was designed for use in depths of up to approximately 1,600 feet as opposed to the maximum of about 125 feet for the ground influence mines; it was used extensively during the war.