serious nuclear and radiation accidents have involved nuclear submarine mishaps. The reactor accident in 1961 resulted in 8 deaths and more than 30 other people were over-exposed to radiation. The reactor accident in 1968 resulted in 9 fatalities and 83 other injuries. The accident in 1985 resulted in 10 fatalities and 49 other radiation injuries. Alternative Oil-fired steam turbines powered the British K-class submarines, built during World War I and later, to give them the surface speed to keep up with the battle fleet. The K-class subs were not very successful, however. Toward the end of the 20th century, some submarines—such as the British Vanguard class—began to be fitted with pump-jet propulsors instead of propellers. Though these are heavier, more expensive, and less efficient than a propeller, they are significantly quieter, providing an important tactical advantage. Armament The success of the submarine is inextricably linked to the development of the torpedo, invented by Robert Whitehead in 1866. His invention is essentially the same now as it was 140 years ago. Only with self-propelled torpedoes could the submarine make the leap from novelty to a weapon of war. Until the perfection of the guided torpedo, multiple "straight-running" torpedoes were required to attack a target. With at most 20 to 25 torpedoes stored on board, the number of attacks was limited. To increase combat endurance most World War I submarines functioned as submersible gunboats, using their deck guns against unarmed targets, and diving to escape and engage enemy warships. The importance of guns encouraged the development of the unsuccessful Submarine Cruiser such as the French and the Royal Navy's and M-class submarines. With the arrival of anti-submarine warfare (ASW) aircraft, guns became more for defense than attack. A more practical method of increasing combat endurance was the external torpedo tube, loaded only in port. The ability of submarines to approach enemy harbours covertly led to their use as minelayers. Minelaying submarines of World War I and World War II were specially built for that purpose. Modern submarine-laid mines, such as the British Mark 5 Stonefish and Mark 6 Sea Urchin, can be deployed from a submarine's torpedo tubes. After World War II, both the US and the USSR experimented with submarine-launched cruise missiles such as the SSM-N-8 Regulus and P-5 Pyatyorka. Such missiles required the submarine to surface to fire its missiles. They were the forerunners of modern submarine-launched cruise missiles, which