The first successful torpedo was developed by Robert Whitehead (standing right in the picture above), a British engineer who demonstrated the new weapon in 1867. It was driven by compressed air and had a range of 700 meters at 7 knots, i.e. 13 kilometers per hour. (1 knot = 1.85 kilometers). By 1889, the range had been doubled and the speed quadrupled, but the accuracy was still unsatisfactory. This defect was overcome by the introduction of gyroscopic stabilizers. By World War II, most countries had developed variants of the original weapon. They were about 6 meters (20 feet) long arid 54 centimeters (21″) in diameter, had a speed of 45 knots, a maximum range of 4.5 kilometers and carried nearly 270 kilograms of high explosive. Millions of tons of shipping fell victim to this weapon.
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Yet there was a rub: Air contains 78% nitrogen, an inert gas that is insoluble in water, so it leaves a trail of bubbles behind a speeding torpedo. This streak of white foam could be readily recognized by the target ship and enabled it to take evasive action. It was after many years that this disadvantage was eliminated by the introduction of battery-driven electric motors to replace the compressed air propellant system.
Today, a torpedo consists of a warhead, battery, motor, propeller and rudder. Most have sophisticated wire-guided system or, alternatively, acoustic homing device. (See diagram above). They are launched by submarines as well as ships and can have a range of 50 kilometers or more.