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.
Cross-section of a Whitehead Torpedo.
Redrawn from the Illustrated London News.
A, Striker which, when driven in, fires the charge; B, Safety pin, which is removed just before the torpedo is discharged; C, Detonating charge; D, Explosive-head, or war-head; filled with guncotton; E, Primer charge of dry guncotton in cylinder; F, Balance chamber; G, Starting pin; H, Buoyancy chamber; I, Propellor shaft; J, Vertical rudder; K, Twin screws; L, Horizontal rudder; M, Gyroscope controlling torpedo’s course; N, Engines propelling machinery; O, Pendulum acting on the horizontal rudder which controls the depth of submergence; P, Hydrostatic valve; Q, Air-chamber, filled with compressed air; provides motive-power for the engines; R, “Jammer” or release propellor.