The necessity of such features as bottom wheels and diving compartment is now being brought out in the present war. I believe the mining and countermining features must be incorporated in one type before the submarine reaches its full development. The impotency of the great combined English and French fleets of battleships, cruisers, destroyers, and submarines must be galling to the people who have paid for them by the sweat of their brows. These fleets are impotent because the Germans will not come out from behind their mines and forts and wage an unequal battle against superior numbers, but prudently are sending out their submarines to destroy gradually the enemy which is trying to blockade the German ports. [Illustration: A MINE AND NET EVADING SUBMARINE UNDER-RUNNING A NET Courtesy of the Scientific American A submarine fitted with a device of this kind can readily under-run any net; running slowly on the bottom the net may be seen through the aquascope or felt with its advanced feelers. Even if mines are attached, divers may cut them loose, or they may be exploded by counter mines to make a safe passage under the nets. Surface ships attempting to guard the nets may be sunk by torpedoes or heavy gun fire from disappearing guns on other submarines, giving the bottom-working submarines ample time to clear away nets and mines.] Winston Churchill, former First Lord of the British Admiralty, expressed the bitterness of this impotency when he said: "If they don't come out and fight, we will go in after them and dig them out like rats"; regrettably, the German mines and submarines stand in the way, and are themselves taking their toll of ships. The mine-evading submarine can enter with comparative safety through a mine field, like a shuttle passing through the woof of cloth during the weaving process, and I take the opportunity to explain this method of entering harbors. To comprehend thoroughly the safety with which this is accomplished, it is necessary to appreciate the almost insuperable difficulty of discovering an object like a submarine vessel when once sunk beneath the surface of the water. There are many sunken ships containing valuable treasures and cargoes that lie along our coast, and in most of the harbors of the world, that have been known to have sunk within a radius of less than a mile from some given point, but which have never been located. Some of these vessels have been searched for for years and never have been found. Dozens of vessels have been sunk in the waters of the North and East Rivers and never have been located. Some of the British and French submarines have been lost in localities well known, but it has been impossible to locate them.