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:
| British Naval Torpedoes of 1870 | |||||
| Length, Feet | Diameter, Inches | Charge, Pounds | Range, Yards | Speed, Knots | |
| Large | 14 | 16 | 67 guncotton | 600 | 7.5 |
| Small | 13 10.58 in. | 14 | 18 dynamite | 200 | 8.5 |
| British Naval Torpedoes of 1915 | |||||
| Large | 21 | 21 | 330 guncotton | 12,000 | 48 |
| Small | 18 | 18 | 200 guncotton | 16,000 | 36 |
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.