Mr. Lake declares that one of his up-to-date wheeled submarines could enter a harbor-mouth defended by booms and nettings that would keep out either surface torpedo boats or ordinary submarines. The smooth-backed bottom-worker of this special type would slip under the netting like a cat under a bead portière. If the netting were fastened down, a diver would step out through the door in the bottom of the submarine and either cut the netting from its moorings or attach a bomb to blow a hole for the bottom-worker to go in through. An ordinary submarine, entering a hostile harbor, would be in constant danger of running aground in shallow water and either sticking there or rebounding to the surface, to be seen and fired at by the enemy. Even if its commander succeeded in keeping to the deep channel by dead reckoning--a process akin to flying blindfolded in an aeroplane up a crooked ravine and remembering just when and where to turn--even if he dodged the rocks and sand bars, he would be liable to bump the nose of his boat against an anchored contact mine (see Chapter XI). But the Lake bottom-worker would trundle steadily along, sampling the bottom to find where it was, and passing safely under the mines floating far above it. The divers would make short work of cutting the mine cables, or they might plant mines of their own under the ships in the harbor and blow them up as Bushnell tried to. Using electric motors and storage air-flasks, with no pipe masts or other “surface-indications” to betray its presence, one of these boats could remain snugly hid at the bottom of an enemy’s harbor as long as its supplies held out. [Illustration: Courtesy of Mr. Simon Lake. Cross-section of Diving-compartment on a Lake Submarine.] As yet, however, we have not heard of any such exploits in the present war, though they seem perfectly feasible. Mr. Lake sold a boat designed for this sort of work and called the _Protector_ to Russia in 1906.