THE RMA MINE. The RMA and its float are shown in figure 109. The purpose of the float was to assure proper planting of the mine by slowing its descent and causing the mine to plant in an upright position. The float incorporated a valve of novel design which allowed water to fill and sink it after the mine reached the bottom and tension on the float cable was released.

Figure 109 – RMA Mine

The RMA mine could operate in any one off the following ways:

1. Normal control mine for firing by observation

2. Normal ground-magnetic mine with the M 1 unit

3. Magnetically monitored by the M 1 unit for night control

4. Remote arming from an observation post by a cable through which the M 1 unit is rendered active at any desired time

Description of Case

Shape

Hemispherical; supported by four wheeled truck

Diameter

50 in.

Height

39 in.

Charge

1,750 lb. block-fitted hexanite

Description of External Fittings

Cover plate

18-3/4 in. diam., on top center of case, flush type, secured by 18 screws

Drogue eye

Screwed into center of cover plate

Hydrostatic clock

6-in. diam., 4 in. from drogue eye, secured by keep ring

Inspection plug

1-in. diam., 12 in. from center of cover plate, screwed into case

Launching buffers

Two pairs on bottom edge of hemisphere, 180° apart. The buffers in each pair are 18 in. apart.

Booster cover plate

4-1/4 in. diam. screwed into bottom center of case

Figure 110 – RMA Mine – Cross Section