The HMA Mine. The HMA Mine is similar in appearance to the HMB mine, with the ex-ception that it has two rows of permanent magnets on its upper side. Its characeristics are as follows: (Specification are approximate.)

Description

Case material

Iron

Length of case

56 in.

Diameter of case

45 in.

Weight of charge

1200 lb.

Maximum depth

165 ft.

Holding strength
of magnets

440 lb.

Positive buoyancy

22 lb.

Method of firng

UES II 6-day clock which is started by a hand-operated mechanical clock starter

The Germans felt that this mine presented the following operational difficulties:

1. It would be difficult for the operator of the submarine to penetrate British defensive installations.

2. It would be difficult for the operator of the submarine to affix the mine to the bot-tom of the target ship.