Zeppelin L1 was 525 feet in length, with a diameter of 50 feet. Some idea of the size may be obtained through the knowledge that she was longer than a modern Dreadnought. The framework was made of specially light metal, aluminium alloy, and wood. This framework, which was stayed with steel wire, maintained the shape and rigidity of her gas-bags; hence vessels of this type are known as RIGID air-ships. Externally the hull was covered with a waterproof fabric. Though, from outside, a rigid air-ship looks to be all in one piece, within it is divided into numerous compartments. In Zeppelin L1 there were eighteen separate compartments, each of which contained a balloon filled with hydrogen gas. The object of providing the vessel with these small balloons, or ballonets, all separate from one another, was to prevent the gas collecting all at one end of the ship as the vessel travelled through the air. Outside the ballonets there was a ring-shaped, double bottom, containing non-inflammable gas, and the whole was enclosed in rubber-coated fabric. The crew and motors were carried in cars slung fore and aft. The ship was propelled by three engines, each of 170 horse-power. One engine was placed in the forward car, and the two others in the after car. To steer her to right or left, she had six vertical planes somewhat resembling box-kites, while eight horizontal planes enabled her to ascend or descend. In Zeppelin L2, which was a later type of craft, there were four motors capable of developing 820 horse-power. These drove four propellers, which gave the craft a speed of about 45 miles an hour. The cars were connected by a gangway built within the framework. On the top of the gas-chambers was a platform of aluminium alloy, carrying a 1-pounder gun, and used also as an observation station. It is thought that L1 was also provided with four machine-guns in her cars. Later types of Zeppelins were fitted with a "wireless" installation of sufficient range to transmit and receive messages up to 350 miles. L1 could rise to the height of a mile in favourable weather, and carry about 7 tons over and above her own weight. Even when on ground the unwieldy craft cause many anxious moments to the officers and mechanics who handle them. Two of the line have broken loose from their anchorage in a storm and have been totally destroyed. Great difficulty is also experienced in getting them in and out of their sheds. Here, indeed, is a contrast with the ease and rapidity with which an aeroplane is removed from its hangar.