In order to be able to make an invasion in force upon Great Britain's cities extremely favourable weather must prevail, and the treacherous nature of the weather conditions of the North Sea are known fully well both to British and Teuton navigators. Seeing that the majority of the Zeppelin pilots are drawn from the Navy and mercantile marine, and thus are conversant with the peculiarities and characteristics of this stretch of salt water, it is only logical to suppose that their knowledge will exert a powerful influence in any such decision, the recommendations of the meteorological savants not withstanding. When the Zeppelin pride of the German Navy "L-1" was hurled to destruction by a typical North Sea squall, Captain Blew of the Victoria Luise, a Zeppelin with many great achievements to her credit, whose navigator was formerly in the Navy, and thus is familiar with the whole issue, explained that this atmospheric liveliness of the North Sea prevails for the most part in the latitude of Norway, but that it frequently extends as far south as the gate of the Channel. He related furthermore that the rain squalls are of tropical violence, while the vertical thrusts of air are such that no dirigible as yet constructed could ever hope to live in them. Under such conditions, he continued, the gas is certain to cool intensely, and the hull must then become waterlogged, not to mention the downward thrust of the rain. Under such conditions buoyancy must be imperilled to such a degree as to demand the jettisoning of every piece of ballast, fuel and other removable weight, including even the steadying and vertical planes. When this has been done, he pointed out, nothing is left with which to combat the upward vertical thrusts of the air. To attempt to run before the wind is to court positive disaster, as the wind is certain to gain the mastery. Once the airship loses steering way and is rendered uncontrollable it becomes the sport of the forces of Nature, with the result that destruction is merely a matter of minutes, or even seconds. Every navigator who knows the North Sea will support these conclusions. Squalls and blizzards in winter, and thunderstorms in summer, rise with startling suddenness and rage with terrific destructive fury. Such conditions must react against the attempt of an aerial invasion in force, unless it be made in the character of the last throw by a desperate gambler, with good fortune favouring the dash to a certain degree. But lesser and more insignificant Zeppelin raids are likely to be somewhat frequent, and to be made at every favourable climatic opportunity. CHAPTER VII. AEROPLANES OF WAR