In England the cylindrical shape has up to quite lately found most favour with her torpedoists for both buoyant and ground mines. At [Fig. 21] is represented a 100-lb. buoyant electrical mine, surrounded by a wooden jacket, e, and having its circuit closer, C, enclosed within it; and at [Fig. 22] is shown a 250-lb. electrical mine, which may be used either as a buoyant or ground one.
For large ground mines, the best form of torpedo case seems to be that of the turtle mine, which is shown at [Fig. 9]. A heavy charge may be contained in it; it forms its own anchor; and it would withstand an explosion of an adjacent mine without sustaining any injury. At present the cylindrical shape is the form generally used, though as far as retaining its position on the ground in a strong tide, it cannot be compared to the turtle form.
FORM OF CASE OF SUBMARINE MINES.
The Conical Shape.—Hitherto this shape of submarine mine case was only used in connection with mechanical mines, but now it is the form considered most suitable for all buoyant mines, electrical or mechanical. At [Fig. 23] is shown the conical shaped mechanical mine, employed by the Confederates for use with sensitive fuzes. The conical form of torpedo case lately approved of by the English torpedo authorities is somewhat similar to that one, the charge being contained in a kind of box hung from the top of the case, and the circuit closer is screwed into the bottom of the case; surrounding the upper part of the case is a thick buffer of wood, by which damage to the mine is prevented by the passage of friendly ships. This is altogether a very neat and serviceable form of torpedo case. This form of case is also more difficult to discover by dragging, and easier to retain in position.
Electrical Fuzes.—The fuzes employed in connection with electrical submarine mines may be divided into two classes:—
1. Platinum wire bridge fuzes.
Note.—That is where the evolution of heat is caused by a large quantity of the electric force flowing through a good conductor of large section, such as the copper core of electric cables, being suddenly checked by a very thin wire composed of a metal which compared with the conductor offers a very great resistance, such as platinum.
2. High tension fuzes.