This does not mean that she cannot make quite long voyages, since a ship of the dimensions we are contemplating could store quite a lot of air. But it does help to determine the strategy of space-warfare. It will be fundamentally a struggle for bases where more oxygen can be obtained. Not through going down into the atmosphere of Earth or the thin atmosphere of Mars or the questionable one of Venus. It means bases on the Moon and the asteroids. The Moon and asteroids are made of rocks, on the surface at least, and practically all rocks are loaded with oxygen--47% in the crust of the Earth for example. With the kind of power that will be available by time we get space-ships, it will be a comparatively simple matter to separate these rock materials from their oxygen electrolytically. Carbon dioxide is partly oxygen, of course, but so stubbornly bonded that no ordinary electrolytic process will break it and it has the unpleasant quality of being a gas under electrolytic conditions. Since the oxygen-producing machinery will be too heavy and bulky to carry aboard the space-ship the job will have to be done at air-refueling stations and these advanced bases will be the key of space-campaigns. Naturally, they will be powerfully fortified against attack from the enemy's space-fleet. Equally naturally they will be logical points of attack in the hope of limiting the enemy's operations by cutting his bases from under him. Thus the overall strategy of a space-campaign will somewhat resemble that of the Pacific War, with each party trying to destroy or neutralize the enemy's bases while extending his own. If both have bases on the Moon or Mars there may even be ground campaigns in support of those in the skies. And getting control of one of those erratic asteroids that come within the orbit of Mars will count for ten. What about armament? In stories of space-warfare that get away from those improbable rays there is usually some kind of hyper-super-duper torpedo, rocket-propelled. But this only demonstrates that the authors of the stories are thinking in Earth-terms instead of space-terms. It is perfectly plausible to include some torpedoes, probably with atomic warheads, in the armament of a space-ship--something that would knock out an enemy base or destroy a space-battleship at a single blow. But the torpedo will always be what military men call a weapon of opportunity. They can't be used at all angles--it would be fatally easy for one of them to make a near-miss on the enemy craft and atom-bomb your own Moon base or some part of the Earth you didn't want atom-bombed. Earth's gravitational attraction would pull such a torpedo in from quite a distance out.