How best to float a charge of explosives against the hull of an enemy’s ship and there explode it is the great problem of torpedo warfare. The spar-torpedo, that did such effective work in the Civil War, was little more than a can of gunpowder on the end of a stick. This stick or spar was mounted usually on the bow of a steam-launch, either partially submerged, like the David, or boldly running on the surface over log-booms and through a hail of bullets and grapeshot, as when Lieutenant Cushing sank the Confederate ironclad Albemarle. Once alongside, the spar-torpedo was run out to its full length, raised, depressed, and finally fired by pulling different ropes. So small was the chance of success and so great the danger to the launch’s crew that naval officers and inventors all the world over sought constantly for some surer and safer way.

Early in the sixties, an Austrian artillery officer attached to the coast defenses conceived the idea of sending out the launch without a crew. He made some drawings of a big toy boat, to be driven by steam or hot air or even by clockwork, and steered from the shore by long ropes. As it would have no crew, this boat could carry the explosives in its hull, and the spars which were to project from it in all directions would carry no torpedoes themselves but would serve to explode the boat’s cargo of guncotton by firing a pistol into it, as soon as one of the spars came into contact with the target. Before he could carry out his ideas any further, this officer died and his plans were turned over to Captain Lupuis of the Austrian navy. Lupuis experimented diligently with surface torpedoes till 1864, but found that he would have to discover some better steering-device than ropes from the shore and some other motive-power than steam or clockwork. So he consulted with Mr. Whitehead, the English manager of a firm of engine manufacturers at the seaport of Fiume.

Whitehead gave the torpedo a fish-shaped hull, so that it could run beneath instead of on the surface. For motive-power he used compressed air, which proved much superior to either steam or clockwork. And by improving its rudders, he enabled the little craft to keep its course without the aid of guide-ropes from the shore. The chief defect of the first Whitehead torpedoes, which were finished and tried in 1866, was that they kept bobbing to the surface, or else they would dive too deep and pass harmlessly under the target. To correct this defect, Whitehead invented by 1868 what he called the “balance chamber.” Then, as now, each torpedo was divided into a number of separate compartments or chambers, and in one of these the inventor placed a most ingenious device for keeping the torpedo at a uniform depth. The contents of the balance-chamber was Whitehead’s great secret, and it was not revealed to the public for twenty years.

The automobile or, as it was then called, the “submarine locomotive” torpedo was now a practicable, though by no means perfected, weapon, and the Austrian naval authorities gave it a thorough trial at Fiume in 1868. Whitehead rigged up a crude ejecting tube on the bow of a gunboat, and successfully discharged two of his torpedoes at a yacht. The Austrian government promptly adopted the weapon, but could not obtain a monopoly of it, for Whitehead was a patriotic Englishman. The British admiralty invited him to England two years later, and after careful trials of its own, induced the English government to buy Whitehead’s secret and manufacturing rights for $45,000. Other nations soon added “Whiteheads” to their navies, and in 1873 there was built in Norway a large, fast steam launch for the express purpose of carrying torpedoes and discharging them at an enemy. Every one began to build larger and swifter launches, till they evolved the torpedo-boat and the destroyer of to-day.

The torpedo itself has undergone a similar development in size and efficiency. The difference between the Whiteheads of forty-five years ago and those of to-day is strikingly shown in the following table:

The length of a large modern torpedo, it will be observed, is only three inches less than that of Fulton’s famous submarine boat of 1801. A Whitehead torpedo is really a small automatic submarine, steered and controlled by the most ingenious and sensitive machinery, as surely as if it were manned by a crew of Lilliputian seamen.

Projecting from the head is the “striker,” a rod which, when the torpedo runs into anything hard, is driven back in against a detonator or “percussion-cap” of fulminate of mercury. Just as the hammer of a toy “cap-pistol” explodes a paper cap, so the sudden shock of the in-driven striker explodes the fulminate, which is instantly expanded to more than two thousand times its former size. This, in turn, gives a severe blow to the surrounding “primer” of dry guncotton. The primer is exploded, and by its own expansion sets off the main charge of several hundred pounds of wet guncotton.

The reason for this is that though wet guncotton is safe to handle because a very great shock is required to make it explode, dry guncotton is much less so, while a shell or torpedo filled with fulminate of mercury would be more dangerous to its owners than to their enemies, because the slightest jar might set it off prematurely. Every precaution is taken to prevent a torpedo’s exploding too soon and damaging the vessel from which it is fired.

When the torpedo is shot out of the tube, by compressed air, like a pea from a pea-shooter, the striker is held fast by the “jammer”: a small propellor-shaped collar, whose blades begin to revolve as soon as they strike the water, till the collar has unscrewed itself and dropped off after the torpedo has traveled about forty feet. A copper pin that runs through the striker-rod is not removed but must be broken short off by a blow of considerable violence, such as would be given by running into a ship’s hull. As a third safeguard, there is a strong safety-catch, that must be released by hand, just before the torpedo is placed in the tube.

The explosive charge of two or three hundred pounds of wet guncotton is called the “war-head.” In peace and for target-practice it is replaced by a dummy head of thick steel. The usual target is the space between two buoys moored a ship’s length or less apart. At the end of a practice run, the torpedo rises to the surface, where it can be recovered and used again. This is distinctly worth while, for a modern torpedo costs more than seven thousand dollars.

Back of the war-head is the air-chamber, that contains the motive-power of this miniature submarine. The air is either packed into it by powerful pumps, on shore or shipboard, or else drawn from one of the storage flasks of compressed air, a number of which are carried on every submarine. The air-chamber of a modern torpedo is charged at a pressure of from 2000 to 2500 pounds per square inch. As the torpedo leaves the tube, a lever on its back is struck and knocked over by a little projecting piece of metal, and the starting-valve of the air-chamber is opened. But if the compressed air were allowed to reach and start the engines at once, they would begin to revolve the propellors while they were still in the air inside the tube. This would cause the screws to “race,” or spin round too rapidly and perhaps break off. So there is a “delaying-valve,” which keeps the air away from the engines till another valve-lever is swung over by the impact of the water against a little metal flap.

As the compressed air rushes through the pipe from the chamber to the engine-room, it passes through a “reducing-valve,” which keeps it from spurting at the start and lagging at the finish. By supplying the air to the engines at a reduced but uniform pressure, this device enables the torpedo to maintain the same speed throughout the run. At the same time the compressed air is heated by a small jet of burning oil, with a consequent increase in pressure, power, and speed, estimated at 30 per cent. All these devices are kept not in the air-chamber itself but in the next compartment, the balance-chamber.

Here is the famous little machine, once a close-kept secret but now known to all the world, that holds the torpedo at any desired depth. Think of a push-button, working in a tube open to the sea, with the water pressure pushing the button in and a spiral spring inside shoving it out. This push-button—called a “hydrostatic valve”—is connected by a system of levers with the two diving-planes or horizontal rudders that steer the torpedo up or down. By turning a screw, the spring can be adjusted to exert a force equal to the pressure of the water at any given depth. If the torpedo dives too deep, the increased water-pressure forces in the valve, moves the levers, raises the diving-planes, and steers the torpedo towards the surface. As the water pressure grows less, the spring forces out the valve, depresses the diving-planes, and brings the miniature submarine down to its proper depth again. When his torpedoes grew too big to be controlled by the comparatively feeble force exerted by the hydrostatic valve, Whitehead invented the “servo-motor”: an auxiliary, compressed-air engine, less than five inches long, sensitive enough to respond to the slightest movement of the valve levers but strong enough to steer the largest torpedo, exactly as the steam steering-gear moves the huge rudder of an ocean liner.

There is also a heavy pendulum, swinging fore and aft and attached to the diving-planes, that checks any sudden up-or-down movement of the torpedo by inclining the planes and restoring the horizontal position.

Next comes the engine-room, with its three-cylinder motor, capable of developing from thirty-five to fifty-five horse-power. The exhaust air from the engine passes out through the stern in a constant stream of bubbles, leaving a broad white streak on the surface of the water as the torpedo speeds to its mark.

The aftermost compartment is called the buoyancy chamber. Besides adding to the floatability of the torpedo, this space also holds the engine shaft and the gear attaching it to the twin propellors. The first Whiteheads were single-screw boats. But the revolution of the propellor in one direction set up a reaction that caused the torpedo itself to partially revolve or heel over in the other, disturbing its rudders and swerving it from its course. This reaction is neutralized by using two propellers, one revolving to the right, the other to the left. Instead of being placed side by side, as on a steamer, they are mounted one behind the other, with the shaft of one revolving inside the hollow shaft of the other, and in the opposite direction.

Long after they could be depended on to keep a proper depth, the Whiteheads and other self-propelled torpedoes were liable to swing suddenly to port or starboard, or even turn completely round. During the war between Chile and Peru, in 1879, the Peruvian ironclad Huascar discharged an automobile torpedo that went halfway to the target, changed its mind, and was coming back to blow up its owners when an officer swam out to meet it and succeeded in turning it aside, for the torpedoes of that time were slow and small as well as erratic.

Nowadays a torpedo is kept on a straight course by a gyroscope placed in the buoyancy chamber. Nearly every boy knows the gyroscopic top, like a little flywheel, that you can spin on the edge of a tumbler. The upper part of this toy is a heavy little metal wheel, and if you try to push it over while it is spinning, it resists and pushes back, as if it were alive. A similar wheel, weighing about two pounds, is placed in the buoyancy chamber of a Whitehead. When the torpedo starts, it releases either a powerful spring or an auxiliary compressed air engine that sets the gyroscope to spinning at more than two thousand revolutions a minute. It revolves vertically, in the fore-and-aft line of the torpedo, and is mounted on a pivoted stand. If the torpedo deviates from its straight course, the gyroscope does not, and the consequent change in their relative positions brings the flywheel into contact with a lever running to the servo-motor that controls the two vertical rudders, which soon set the torpedo right again.

Thus guided and driven, a modern torpedo speeds swiftly and surely to its target, there to blow itself into a thousand pieces, with a force sufficient to sink a ship a thousand times its size.

The Whitehead is used by every navy in the world except the German, which has its own torpedo: the “Schwartzkopf.” This, however, is practically identical with the Whitehead, except that its hull is made of bronze instead of steel and its war-head is charged with trinitrotuluol, or T.N.T., a much more powerful explosive than guncotton.

After the Russo-Japanese War, when several Russian battleships kept afloat although they had been struck by Japanese torpedoes, many naval experts declared that an exploding war-head spent most of its energy in throwing a great column of water up into the air, instead of blowing in the side of the ship. So Commander Davis of the United States navy invented his “gun-torpedo.” This is like a Whitehead in every respect except that instead of a charge of guncotton it carries in its head a short eight-inch cannon loaded with an armor-piercing shell and a small charge of powder. In this type of torpedo, the impact of the striker against the target serves to fire the gun. The shell then passes easily through the thin side of the ship below the armor-belt and through any protecting coal-bunkers and bulkheads it may encounter, till it reaches the ship’s vitals, where it is exploded by the delayed action of an adjustable time-fuse. What would happen if it burst in a magazine or boiler-room is best left to the imagination. Several Davis gun-torpedoes have been built and used against targets with very satisfactory results, but they have not yet been used in actual warfare.

Mr. Edward F. Chandler, M.E., one of the foremost torpedo-experts in America, is dissatisfied with the compressed-air driven gyroscope, both because it does not begin to revolve till after the torpedo has been launched and perhaps deflected from its true course, and because it cannot be made to spin continuously throughout the long run of a modern torpedo. He proposes to remove the compressed-air servo-motors, both for this purpose and for controlling the horizontal rudders by the hydrostatic valve, and replace them with an electrical-driven gyroscope and depth-gear. The increased efficiency of the latter would enable him to get rid of the heavy, uncertain pendulum, thus allowing for the weight of the storage batteries. Mr. Chandler declares that his electrically-controlled torpedo can be lowered over the side of a small boat, headed in any desired direction, and started, without any launching-tube.9

Though the automobile torpedo has been brought to so high a state of perfection, the original idea of steering from the shore has not been abandoned. The Brennan and Sims-Edison controllable torpedoes were driven and steered by electricity, receiving the current through wires trailed astern and carrying little masts and flags above the surface to guide the operator on shore. But these also served as a warning to the enemy and gave him too good a chance either to avoid the torpedo or destroy it with machine-gun fire. Then, too, the trailing wires reduced its speed and were always liable to get tangled in the propellors. Controllable torpedoes of this type were abandoned before the outbreak of the present war and will probably never be used in action.

A new and more promising sort of controllable torpedo was immediately suggested by the invention of wireless telegraphy. Many inventors have been working to perfect such a weapon, and a young American engineer, Mr. John Hays Hammond, Jr., seems to have succeeded. From his wireless station on shore, Mr. Hammond can make a small, crewless electric launch run hither and yon as he pleases about the harbor of Gloucester, Massachusetts. The commander and many of the officers of the United States coast artillery corps have carefully inspected and tested this craft, which promises to be the forerunner of a new and most formidable species of coast defense torpedo.