Submarine mine consists of an explosive charge enclosed in a mater-tight case, and a firing device, the whole intended to be submerged in a steray which it is desired to close against the passage of an enemys vessels. They should not, in general, be used where the depth of water is less than 90 feet. In the ground mine, the case contains the explosive and the firing device, and is heavier than the tiisplaced water it therefore rests upon the bottom and requires no anchor. Ground mines are not used where the depth of water exceeds 35 feet...... | Manual For Submarine Mining by R W Finger, Paperback | Indigo Chapters