By that time Nazi Germany had been defeated, but Japan was still fighting. Two more devices were prepared. After a warning, one was exploded over the Japanese city of Hiroshima on August 6, 1945, and the other over Nagasaki 2 days later. The Japanese government surrendered and World War II came to an end. It was with the blast over Hiroshima that the world came to know it was in the nuclear age and that the ferocious weapon of the nuclear bomb existed. (The popular name for it at the time was “atomic bomb” or “A-bomb”.) During the war, German scientists may have been trying to develop a nuclear bomb, but, if so, they had not yet succeeded at the time Germany met its final defeat. Soviet physicists, under Igor Vasilievich Kurchatov (1903-1960), were also working on the problem. The dislocation of the war, which inflicted much more damage on the Soviet Union than on the United States, kept the Soviet effort from succeeding while it was on. However, since the Soviets were among the victors, they were able to continue after the war. In 1949 the Soviets exploded their first nuclear bomb. In 1952 the British did the same; in 1960, the French; and in 1964, the Chinese. Although many nuclear bombs have been exploded for test purposes, the two over Hiroshima and Nagasaki have been the only ones used in time of war. Nor need nuclear bombs be considered as having destructive potential only. There is the possibility that, with proper precautions, they might be used to make excavations, blast out harbors or canals, break up underground rock formations to recover oil or other resources, and in other ways do the work of chemical explosives with far greater speed and economy. It has even been suggested that a series of nuclear bomb explosions might be used to hurl space vehicles forward in voyages away from earth. Nuclear Reactors The development of the nuclear chain reaction was not in the direction of bombs only. Nuclear reactors designed for the controlled production of useful energy multiplied in number and in efficiency since Fermi’s first “pile”. Many nations now possess them, and they are used for a variety of purposes.[2] [Illustration: _The USS_ Nautilus, _the world’s first nuclear powered submarine, in New York harbor_.] In 1954 the first nuclear submarine the USS _Nautilus_ was launched by the United States. Its power was obtained entirely from a nuclear reactor, and it was not necessary for it to rise to the surface at short intervals in order to recharge its batteries. Nuclear submarines have crossed the Arctic Ocean under the ice cover, and have circumnavigated the globe without surfacing. In 1959 both the Soviet Union and the United States launched nuclear-powered surface vessels. The Soviet ship was the icebreaker, _Lenin_, and the American ship was a merchant vessel, the NS _Savannah_.