Hydrogen-2, therefore, is the one to pin hopes on especially in conjunction with hydrogen-3. Only 1 atom out of every 6000 hydrogen atoms is hydrogen-2, but that is enough. There exists a vast ocean on earth that is made up almost entirely of water molecules and in each water molecule 2 hydrogen atoms are present. Even if only 1 in 6000 of these hydrogen atoms is deuterium that still means there are about 35,000 billion tons of deuterium in the ocean. What’s more, it isn’t necessary to dig for that deuterium or to drill for it. If ocean water is allowed to run through separation plants, the deuterium can be extracted without very much trouble. In fact, for the energy you could get out of it, deuterium from the oceans, extracted by present methods and without allowing for future improvement, would be only one-hundredth as expensive as coal. The deuterium in the world’s ocean, if allowed to undergo fusion little by little, would supply mankind with enough energy to keep us going at the present rate for 500,000,000,000 years. To be sure, to make deuterium fusion practical, it may be necessary to make use of rarer substances such as the light metal lithium. This will place a sharper limit on the energy supply but even if we are careful, fusion would probably supply mankind with energy for as long as mankind will exist. Then, too, there would seem to be no danger of hydrogen fusion plants running out of control. Only small quantities of deuterium would be in the process of fusion at any one time. If anything at all went wrong, the deuterium supply could be automatically cut off and the fusion process, with so little involved, would then stop instantly. Moreover, there would be less reason to worry about atomic wastes, for the most dangerous products—hydrogen-3 and neutrons—could be easily taken care of. It seems ideal, but there is a catch. However clear the theory, before a fusion power station can be established some practical method must be found to start the fusion process, which means finding some way for attaining temperatures in the millions of degrees. One method for obtaining the necessary temperature was known by 1945. An exploding fission bomb would do it. If, somehow, the necessary hydrogen-2 was combined with a fission bomb, the explosion would set off a fusion reaction that would greatly multiply the energy released. You would have in effect a “thermonuclear bomb”. (To the general public, this was commonly known as a “hydrogen bomb” or an “H-bomb”.) In 1952 the first fusion device was exploded by the United States in the Marshall Islands. Within months, the Soviet Union had exploded one of its own and in time thermonuclear bombs thousands of times as powerful as the first fission bomb over Hiroshima were built and exploded.