All the ships were built of the light and tensile metal Firmium, which is lighter and much stronger than the metal called Steel, which was so much used by our ancestors. Most of them were cigar-shaped, but others were much flatter, and there were a few that were very long and thin. The largest were about 300 yards in length; the rest varied in proportion down to the torpedo-boats, which were only 15 yards long.
All the ships were built on the same principle. The outside of the hull was surrounded by a thick sheathing of Firmium, and there was a powerful ram at both ends. The inside was divided into a number of decks, according to the size of the vessel. These, again, were divided into compartments by air-tight doors, so that if the hull were pierced by a shot the air would only escape from one compartment, and thus the rest of the crew would not be harmed. Air in the liquid state was stored in reservoirs in the middle of
