The percussion cap is simply a little copper cup and in it is placed a small charge of an explosive which is easily detonated by the percussion of the pin, that is by the pin striking it. The explosive mostly used in percussion caps is mercuric fulminate, which is a compound formed of mercury, carbon, nitrogen, and oxygen.
Since it is the violent explosion of the percussion charge which strikes the main charge of the high explosive in the warhead, and the fire made by the explosion of the percussion charge has nothing to do with it, the main charge of guncotton, where this explosive is used, is often wet down with water before it is packed in, for by so doing a great deal more of it can be put in the same-sized space.
A safety pin (see [Fig. 38]) is set into the firing pin, so that by no possible chance can the latter pin work loose and explode the charge until it strikes the ship it is intended to destroy. Also the butterfly-nut, which I spoke of above, is used as a further safety factor.
The safety pin is simply a pin which is threaded on one end and which extends down through the steel casing of the warhead and screws into the firing pin, or pistol, and holds it securely so that it cannot strike back against the charge until it is unscrewed and taken out or broken off, when it strikes the ship.
The butterfly-nut is simply a thumb nut with a couple of wings on it. When the torpedo is shot out of the torpedo tube the butterfly-nut, which is screwed up close to the warhead on the firing pin, begins to unscrew itself by the action of the water on the wings, which now form little propeller blades; by the time the nut reaches the end of the firing pin and drops off, the torpedo is quite a distance from the submarine which shot it. In this way, all danger of the torpedo’s exploding when it is in, or leaving, the submarine, is done away with. [Fig. 38] shows a cross-section of the warhead and just how the detonating mechanism is made and works.
FIG. 38. THE BUSINESS END OR WAR HEAD OF A REAL TORPEDO
The warheads of the latest torpedoes, especially those used by the Germans, are fitted with steel cutters, so that they can cut their way through nets which ships may spread out to protect themselves.
The Body of the Torpedo.—The next part of the torpedo is the body, and there are five separate and distinct parts to it. These we have named in the order of their position, and they are,
(1) The air pressure chamber; (2) the balance chamber; (3) the power chamber; (4) the buoyancy chamber, and (5) the tail-piece which supports the propellers and the rudders.