804 TORPEDO changes in naval architecture, which have pro- duced iron-clad vessels capable of enduring for a few moments the heaviest fire of modern artillery, have rendered it necessary to devise means of striking the remaining vulnerable points, viz., the deck and the bottom. The former can be attacked advantageously in many localities only by the vertical fire of mortars ; the latter can be most effectively assailed by the torpedo. The chief nations have accordingly established special schools for investigating the subject of submarine warfare, and all possible secrecy is thrown around these studies. In the United States, Great Britain, and other countries a distinction is made between the de- fensive and offensive branches. The American school for defensive torpedoes is at Willet's Point, New York harbor. The general princi- ples which must govern this service are well established. The most vulnerable points of maritime nations are now their great seaboard cities; hence it is of primary importance to pro- tect the seaports. The invention of the screw propeller and of iron armor has enabled fleets to steam rapidly past the forts, under cover of night or fog, and anchor securely in posi- tions where their fire can either destroy the city or compel the payment of an enormous ransom. The great problem of coast defence is, therefore, to devise an effective obstruc- tion of the channel, which, while allowing the free passage of friendly vessels, shall bar the way to an enemy. This is supplied by de- fensive torpedoes planted and operated from the forts. If by their aid the enemy can be detained 100 hours under the fire of the forts, when without it he could pass in one hour, the number of the guns is virtually multiplied by 100. For these reasons military engineers are giving the closest possible study to defensive torpedoes, or submarine mines as they are of- ten called. While the details of our system of submarine defences are not made public, its general features have been announced. In a deep casemate of the fort, secure from the fire of the enemy, are placed electrical batteries, operating apparatus, testing galvanometers, &c., under the charge of a thoroughly trained engineer sergeant. A telegraph wire keeps him in constant communication with his offi- cer, who is posted at some commanding point, where the whole channel lies like a map before him. Radiating from the casemate, in subter- ranean galleries, the torpedo cables extend to the channel, where they terminate in multiple groups of mines so arranged as to be perfectly flanked by the guns of the work. The details of these mines are not public, but an idea of their general construction can probably be formed from fig. 1, which represents the Aus- trian type. It consists of an anchor, a; a buoyant case, 5, containing the charge, fuse, and circuit-closing apparatus ; and the electric cable, <Z, extending to the operating room on shore. These groups are so placed, in succes- sive lines and outlying mines, as to render it FIG. 1. Austrian Submarine Mine. impossible for a vessel to pass without moving over some of them. Thickly rising, but never exposed to view, are numerous buoys, each con- taining a simple electrical apparatus, which in- stantly reports to the ser- geant the locality of any vessel touching them. If friendly, the ship passes in safety; but if an enemy, a single motion of the sergeant makes every mine an auto- matic agent of destruction, ready to deal a tremendous blow at the precise instant when it will be most effec- tive. As the buoys may be slightly in rear of the mines, all attempts to protect the vessel by outrigging frames or nets are futile. Any boat attempting to grapple the torpedoes by night will be overwhelmed by a fire of grape or case shot from the fort, fired automatically by electricity, without the agency of the sol- diers sleeping quietly by the guns. The mines are as effective a year after they are planted as when first laid; and if a single cable be injured or a single charge be wet, the fact is automatically reported, and within five min- utes after the injury has occurred its exis- tence and nature are known in the fort. A mine can be fired without the aid of the buoys. For secondary channels, the use of which could be sacrificed for a time, less elaborate kinds of torpedoes are provided, not unlike those em- ployed by the confederates in the late war. These mines, once planted, are dangerous alike to friend and foe, as they explode on contact with any vessel. The electric light is employed to aid the forts in arresting operations attempt- ed under cover of the night. Where constant currents exist, as in rivers, use can sometimes be made of double drifting torpedoes, so ar- ranged as to foul with the connecting rope the hawsers of vessels at anchor. On the torpe- does being brought alongside by the force of the current, the same agency, acting on a sim- ple piece of mechanism, soon releases a ham- mer and causes an explosion. Offensive tor- pedoes are employed in the battles of vessels with vessels, and require technical naval skill. They are various in principle, and are receiv- ing the careful study of many naval officers of all nations. The American school for offen- sive torpedoes is at Newport, R. I. The prin- cipal types of this class are the following; spar torpedoes, automatic fish torpedoes, otter or Harvey torpedoes, submarine rockets, and submarine boats. Besides these, there is a mixed class, that of fish torpedoes, which may be directed and controlled through the agency of electricity. These last may be either offen- sive or defensive. The spar torpedo has given occasion for some of the most brilliant naval
