The floor of the conning-tower took an angle of about sixty degrees, and Lennard gripped the holdfasts, of which there were two on each wall of the tower. He heard a rush of overwhelming waters--then came darkness. The _Ithuriel_ rushed forward at her highest speed. Then something hit the sea, and a quick succession of shocks sent a shudder through the vessel. "I thought so," said Erskine. "That's John Castellan's combined airship and submarine right enough, and that was an aerial torpedo. If it had hit us when we were above water, we should have been where those French chaps are now. You're quite right, this sort of naval warfare is getting rather exciting." CHAPTER X FIRST BLOWS FROM THE AIR The _Flying Fish_, the prototype of the extraordinary craft which played such a terrible part in the invasion of England, was a magnified reproduction, with improvements which suggested themselves during construction, of the model whose performances had so astonished the Kaiser at Potsdam. She was shaped exactly like her namesake of the deep, upon which, indeed, her inventor had modelled her. She was one hundred and fifty feet long and twenty feet broad by twenty-five feet deep in her widest part, which, as she was fish-shaped, was considerably forward of her centre. She was built of a newly-discovered compound, something like papier-mache, as hard and rigid as steel, with only about one-tenth the weight. Her engines were of the simplest description in spite of the fact that they developed enormous power. They consisted merely of cylinders into which, by an automatic mechanism, two drops of liquid were brought every second. These liquids when joined produced a gas of enormously expansive power, more than a hundred times that of steam, which actuated the pistons. There were sixteen of these cylinders, and the pistons all connected with a small engine invented by Castellan, which he called an accelerator. By means of this device he could regulate the speed of the propellers which drove the vessel under water and in the air from sixty up to two thousand revolutions a minute. The _Flying Fish_ was driven by nine propellers, three of these, four-bladed and six feet diameter, revolved a little forward amidships on either side under what might be called the fins. These fins collapsed close against the sides of the vessel when under water and expanded to a spread of twenty feet when she took the air. They worked on a pivot and could be inclined either way from the horizontal to an angle of thirty degrees. Midway between the end of these and the stern was a smaller pair with one driving screw. The eighth screw was an ordinary propeller at the stern, but the outside portion of the shaft worked on a ball and socket joint so that it could be used for both steering and driving purposes. It was in fact the tail of the _Flying Fish_. Steering in the air was effected by means of a vertical fin placed right aft.