One of the most dangerous and powerful of these deadly destroyers at the time of the breaking out of the Japanese war was the _Octopus_, launched at night, with great secrecy, near the naval station of Sasebo. Her length was eighty feet, diameter eleven feet, displacement (when submerged) one hundred and thirty-nine tons. When she was running light, or "awash," the twin-screws, operated by triple expansion engines worked by steam, gave a speed of fifteen knots, with a minimum endurance, at this speed, of twelve hours. To drive the craft when submerged a battery of storage cells supplied an electric current to operate motors sufficient to give a speed of eight knots for at least six hours. Her armament consisted of five automobile torpedoes and two expulsion tubes, which opened through her black prow like the nostrils of some hideous sea-monster. She was able to sink to a depth of twenty feet below the surface within one minute after the order to dive was given. When she was submerged three feet the pilot obtained a view over the water by means of a _camera lucida_ in a tube that projected above the surface. When Jules Verne wrote _Twenty Thousand Leagues under the Sea_, in 1873, his _Nautilus_ was deemed by the reader untaught in naval constructive history a wild creation of the author's fancy, like his passenger-car shot to the moon from an enormous cannon. To-day there is not a naval commander who would not look grave and consider an immediate withdrawal of his ship when told an enemy's submarine was cruising in his neighbourhood. In the face of open danger, visible to eye and ear, no officer of the navy blenches. The submarine is out of sight. It may be within a hundred yards of the ship when the report is brought. A man who will stand up against a wild beast or a band of savages without a tremor will turn white and shriek with terror if, when he is in the water, the cry of "Shark!" is raised. The shark betrays its presence by its black dorsal fin above the surface of the sea. When the fin disappears the danger increases, becomes terrible; the fear of the swimmer in the vicinity of that black, unseen peril overmasters him. The submarine sinks, like the shark, to attack. Its gleaming back, surmounted by the small, round conning tower, disappears amid a swirl of foam. A single staff at the stern betrays its presence for a moment; then that, too, glides beneath the surface. Not a man on the battle-ship but shudders at the thought of that hidden monster under the waves, driven by the skill and hatred of the human brain. Only tried and absolutely reliable men are chosen for the crew of the submarine. They must be ready to endure extreme discomfort and hardship and must hold their lives in their hands. A well-aimed shot from a war-ship, or a defect in the delicate machinery of the boat, and all is over. A submarine never is wrecked; it sinks, with all on board; it is obliterated.