The first of them is the shape of the ship. The torpedo-shape with brief wings, the type usually pictured, is very attractive. It is the only shape that could take off from earth and go out through the atmosphere. It keeps the machinery well away from the living spaces. For landing on the moon or an asteroid it is quite all right because it can be turned over and set down on its tail jets. But when space-warfare really gets going the torpedo-shape will take a back space before a vessel built in space (probably at a satellite station) to operate and fight in space. And the shape of that ship will be a sphere. It is the strongest, the most economical for the use of the contained cubic capacity, but these are not the main reasons for building space-warships round. The reasons are those of military efficiency, which take precedence over all others when it comes to designing fighting equipment. In the first place a sphere can be given more than one rocket exhaust. With more than one the spherical ship would have a maneuvering ability making immeasurably superior to the long, graceful torpedo. The latter would have to sweep around in curves of hundreds or thousands of miles, or change its course on gyros, which would take nearly as long. But the sphere, with a simple opposite-direction blast from its rockets, could halt, change course and be off. Probably only two exhausts are necessary, but those we have to have. I am aware that the engineering problems of building a space-ship that way are very severe but so are the engineering problems of building an atomic submarine or a carrier to carry jet planes. However, when there is urgent military necessity for something, neither expense nor the difficulty of the problem is ever really allowed to stand in the way. In the second place a sphere can be built with no blind angles of approach. The fighter airplane of today, with an enemy on his tail, is in trouble--and so will be a space-ship with an enemy on its exhaust. Of course, turrets can be mounted above or below the exhaust on a torpedo-shaped ship but they will never give quite the same protection as not having any blind angles at all. In the third place the sphere is the most convenient shape for landing on the Moon or asteroids and they are going to be important as bases. And in the fourth place the armor of the sphere can carry the main structural stresses, making the interior structure light. Using a spherical shape means size, of course, but so do several other necessary factors and it is impossible to avoid them all. This means that the warships of space will not be divided into classes of battleships, cruisers and destroyers like warships of the ocean. With an exception to be noted later all will be battleships. There is no reason for making them anything else.