A submarine of the mine-planting and mine-evading type may, by means of its periscope, range finders and direction indicators, ascertain the exact distance and bearing of vessels at their anchorage. On securing this exact knowledge the submarine may then be submerged to the bottom and creep up under the anchored craft and plant a mine under her which may be exploded by electricity after the submarine has backed a safe distance away, or a mine might be fitted with a powerful magnet and allowed to ascend (by the diver) until it attaches itself to the bottom of the ship.] The diagrammatic sketches illustrate the "Lake" method of operation in cutting cables, evading mines, planting countermines, clearing away mines, or passing under chains, cables, and nets that may be stretched across the entrances of the harbors to effectively stop the progress of surface vessels and submarines not fitted with bottom wheels. [Illustration: SUBMARINE SUPPLY STATION (Drawing by Robt. G. Skerrett.) Illustrating the use of the submarine supply station, which may be anchored on the bottom in positions known only to the commanders of submarines, who may visit such station and renew their supplies of fuel, foodstuffs and torpedoes. The submarine boat approaches alongside of the supply boat, then, by utilizing the air lock, divers may pass out of the submarine and enter into the supply boat through its air lock compartment. A hose may be led from the fuel tanks of the submarine to the fuel supply tanks in the submerged station, compressed air admitted to the tanks and fuel driven from the submarine station to the military submarine. The author's experimental cargo-carrying submarine as tested out in 1900, proved the practicability of transferring cargo from one submerged vessel to another submarine, all the operations being performed under water.] The diving compartment is another feature of submarine construction which has been neglected by the majority of the world's naval authorities. This device is of value not only to vessels of the type just described, but is of general usefulness to all submarines of whatever size or speed. A submarine crew is able by this means to go outside the vessel while submerged and make repairs on the propellers, periscopes, and other exterior parts without the necessity of rising to the surface or of returning to their base. Further, it is capable of use in such a way as to add immensely to the cruising radius of submarines. The method by which this may be accomplished I will briefly outline.