In front of the desk and above the little steering-wheel there was a mahogany board studded with two sets of ivory buttons, disposed in two lines of six each. He touched one of these, and Lennard saw him disappear through the floor of the conning-tower. Within a few moments the portion of the floor upon which he had stood returned to its place, and Lennard said to himself: "If the rest of her works like that, she ought to be a lovely study in engineering." While Captain Erskine is communicating his instructions to his second in command, and arranging the details of the coming fight, there will be time to give a brief description of the craft on board of which Lennard so unexpectedly found himself, and which an invention of his own was destined to make even more formidable than it was. To put it as briefly as possible, the _Ithuriel_ was a combination of destroyer, cruiser, submarine and ram, and she had cost Erskine three years of hard work to think out. She was three hundred feet long, fifty feet broad, and thirty feet from her upper keel to her deck. This was of course an abnormal depth for a vessel of her length, but then the _Ithuriel_ was quite an abnormal warship. One-third of her depth consisted of a sinking-chamber, protected by twelve-inch armour, and this chamber could be filled in a few minutes with four thousand tons of water. This is of course the same thing as saying she had two waterlines. The normal cruising line gave her a freeboard of ten feet. Above the sinking-tanks her vitals were protected by ten-inch armour. In short, as regards armour, she was an entire reversal of the ordinary type of warship, and she had the advantage of being impervious to torpedo attack. Loaded torpedoes had been fired at her and had burst like eggs against a wall, with no more effect than to make her heel over a few degrees to the other side. Submarines had attacked her and got their noses badly bruised in the process. It was, indeed, admitted by the experts of the Admiralty that under water she was impregnable. Her propelling power consisted of four sets of engines, all well below the waterline. Three of these drove three propellers astern: the fourth drove a suction screw which revolved just underneath the ram. This was a mass of steel weighing fifty tons and curved upwards like the inverted beak of an eagle. Erskine had taken this idea from the Russian ice-breakers which had been designed by the Russian Admiral Makaroff and built at Elswick. The screw was protected by a steel grating of which the forward protecting girder completed the curve of the stem. Aft, there was a similar ram, weighing thirty tons and a like protection to the after-screws.