TORPEDO (Lat. torpedo, numbness, cramp fish, torpedo, from torpera, to be numb, stupid). A naval torpedo is an explosive device designed to destroy or injure a ship by blowing a hole in her hull at or below the water line. It consists essentially of the explosive charge, the fuse (which ignites the charge), and the case contain ing these. Torpedoes are of two classes, fixed and moving. Fixed torpedoes are now commonly called torpedo mines or submarine mines.
Torpedo mines are (1) self-acting, and (2) controlled, according to the conditions of firing. Self-acting mines are mechanically or electrically fired. The mechanical arrangements are of nu merous types, but the most common is a set of pins projecting from the head of the torpedo, any one of which if struck would be driven down upon a fulminate primer in communication with the charge. The electrically fired are (1) simple buoyant mines, anchored so as to be not less than 5 nor more than 20 feet below water, and (2) combination ground mines with a buoyant con tact piece or float which is anchored so as to be about the same distance beneath the water as a contact torpedo. In both these types the explo sion is caused by the completion of the electric circuit by the driving in of a pin by a ship which strikes the mine or float.
Controlled mines are (1) automatic and (2) observation. The firing wires for all controlled mines lead to mine stations. For automatic mines this is done merely to secure safety. When the circuit is closed at the mine station the tor pedo is not fired, but merely prepared to explode if one of the contact pieces on the shell is pressed down by a passing ship. The combination con trolled torpedo, like the combination self-acting, is a ground/mine with a contact float; it is made ready in the same way as an automatic con trolled mine. Observation mines are fired by ob servers who keep the circuit closed at their sta tions when the ship is on line with torpedoes as seen from their points of view. Therefore, when a ship is directly over a torpedo, the cir cuits at both mine stations (usually placed so as to give nearly right angle intersection of lines of sight on each torpedo) are closed and the charge is exploded. Observation mines may be of the simple or compound buoyant type or of the ground type. The simple buoyant mine can only be exploded by the observers; the compound type has extra fittings, so that it may he consid ered as belonging also to the automatic buoyant type or controlled mine. Observation, ground mines are simple if fitted for explosion by the observers only, and are combination if they also have contact floats.
Mines of all the types mentioned are in com mon use, their various characteristics fitting them to different local conditions. Self-acting mines have the advantages of (1) being compara tively cheap, (2) can be kept in store ready for immediate use, (3) do not require specially trained men or observation mining stations, and (4) extempore ones can be easily made. But self acting mines are all ( 1) rather dangerous to put out or pick up, (2) the condition of the igniting apparatus cannot be tested after the mine is placed in position, (3) they are as dangerous to friend as to foe when once placed, and (4) the mechanical or electric contact pins may become so overgrown with barnacles as to prevent their operation. After being two months in the water the Spanish self-acting torpedoes (in 1898) were so overgrown with barnacles that none were in a condition in which they would have been exploded if struck by a ship; indeed, two United States ships actually struck them without causing ex plosion. The objections to this type are evidently so serious as to preclude their use in important channels. In such places, particularly if it is desired to keep open a passage for friendly ves sels, observation mines are used. If the water is not too deep, ground mines arc laid; but in deep water buoyant mines must be employed. Where the water is very deep and the currents are strong the mining of a channel is very difficulf in some cases it is impossible to lay them so that they can always be operated effectively.
Self-acting mines are usually placed singly and far enough apart to prevent the explosion of one mine from setting off the others by shock. Controlled mines, and particularly the observa tion variety, are commonly put out in groups, all the mines in each group being exploded simul taneously. When so arranged, each group should be far enough from the others to avoid being ex ploded by shock. The distance at which sym pathetic explosion takes place varies with the character of the explosive and the weight of the charge. Guncotton is commonly use. Its ex treme destructive horizontal range, according to General Abbott, U. S. A., is 14.7 feet for a 100 pound charge, 20.5 feet for a 200-pound charge, and 31.7 feet for a 500-pound charge; while the safety interval or distance between mines or groups should he at least eight times the extreme destructive horizontal range.