She was submerged as the _Ithuriel_ was, by pumping water into the lower part of her hull. When these chambers were empty she floated like a cork. The difference between swimming and flying was merely the difference between the revolutions of the screws and the inclination of the fins. A thousand raised her from the water: twelve hundred gave her twenty-five or thirty miles an hour through the air: fifteen hundred gave her fifty, and two thousand gave her eighty to a hundred, according to the state of the atmosphere. Her armament consisted of four torpedo tubes which swung at any angle from the horizontal to the vertical and so were capable of use both under water and in the air. They discharged a small, insignificant-looking torpedo containing twenty pounds of an explosive, discovered almost accidentally by Castellan and known only to himself, the German Emperor, the Chancellor, and the Commander-in-Chief. It was this which he had used in tiny quantities in the experiment at Potsdam. Its action was so terrific that it did not rend or crack metal or stone which it struck. It overcame the chemical forces by which the substance was held together and reduced them to gas and powder. And now, after this somewhat formal but necessary description of the most destructive fighting-machine ever created we can proceed with the story. There were twenty _Flying Fishes_ attached to the Allied Forces, all of them under the command of German engineers, with the exception of the original _Flying Fish_. Two of these were attached to the three squadrons which were attacking Hull, Newcastle and Dover: three had been detailed for the attack on Portsmouth: two more to Plymouth, two to Bristol and Liverpool respectively, on which combined cruiser and torpedo attacks were to be made, and two supported by a small swift cruiser and torpedo flotilla for an assault on Cardiff, in order if possible to terrorise that city into submission and so obtain what may be called the life-blood of a modern navy. The rest, in case of accidents to any of these, were reserved for the final attack on London. When the _Ithuriel_ disappeared and his torpedo struck a piece of floating wreckage and exploded with a terrific shock, John Castellan, standing in the conning-tower directing the movements of the _Flying Fish_, naturally concluded that he had destroyed a British submarine scout. He knew of the existence, but nothing of the real powers of the _Ithuriel_. The only foreigner who knew that was Captain Count Karl von Eckstein, and he was locked safely in a cabin on board her.