No attack seemed possible without warning, either by sea or above the clouds, for the hostile air-ships could not approach without being seen from a great distance through the clear, starlit sky, and without their lights, which would instantly betray their presence, it was impossible for the submarine vessels even to find the coast. Hour after hour passed, and still no hostile sign rewarded the vigilance of the defenders. No one of the present day could have guessed that all the preparations had been made for such a battle as had never been fought before on sea or land, or in the air. Nothing was visible but the snow-covered earth and the storm-swept sea, for the sentinel ships, floating far above the clouds, were beyond the reach of vision. And yet, if the combined fleets of the modern world had attacked Kerguelen that night, not a ship would have escaped to tell the tale of annihilation, so terrible were the engines of destruction which waited but the signal of battle to strike their swift and irresistible blows. It was about half-past six o’clock the next morning when Alexis, who was on watch in the conning-tower of the _Narwhal_, saw a faint beam of light illuminating the water a long way ahead. He instantly signalled to Alan--“Enemy in sight. Back. I am going to ram.” Alan, unwilling to leave the new crew, who were not yet perfectly acquainted with the working of the machinery, had taken command of the engine-room alternately with Alexis, who was now taking his four hours’ watch in the conning-tower, and to whom the fortune of war had given the honour of striking the first blow. The _Narwhal_ backed rapidly, and as she did so Alexis turned a small wheel in the side of the conning-tower, and the whole chamber sank into the hull of the vessel. As soon as it stopped he pulled a lever and a heavy steel sheet slid over the opening where the glass dome had been. In front of him as he stood at the steering-wheel was a long, very slender needle hung with extreme delicacy on a pivot, up which an electric current constantly passed. This needle was terrestrially insulated by a magnet which always swung opposite to the magnetic pole, and when acted upon only by the steel of the vessel’s fabric, swung indifferently as long as there was no other vessel within a thousand yards of the _Narwhal_. But the moment one came within that distance the needle pointed towards it with unerring accuracy, as it was doing at the present moment. Alexis allowed the vessel to back until he saw the needle begin to waver. Then he knew that the thousand-yard limit had been reached, and signalled-- “Full speed ahead.” The next moment the engines were reversed and the _Narwhal_ bore down on her invisible prey. The needle became rigid again. Alexis kept it pointing dead ahead as the _Narwhal_ gathered way and rushed silently but with irresistible force upon her victim.