repeated failures; but neither he, nor any of his fellow countrymen, advanced the common cause by the suggestion of a single idea of value. Finally, when the German Admiralty, after the failure of their own Howaldt boat, decided to borrow the Holland type from America, it was no German, but the Franco-Spanish engineer d’Equevilley, who designed for them the first five U-boats, of which all the later ones are modifications. The English Admiralty were in no such straits. They were only one year before the Germans in adopting the Holland type; but the native genius at their disposal has enabled them to keep ahead of their rivals from that day to this, in the design, efficiency, size, and number of their submarine vessels. And this result is exactly what might have been expected from the history of submarine invention. The construction of a workable submarine depends upon the discovery and solution of a number of problems, the first five of which may be said to be the problems of-- 1. Submersion. 2. Stability. 3. Habitability. 4. Propulsion and Speed. 5. Offensive Action. If we take these in order, and trace the steps by which the final solution was approached, we shall be able to confirm what has been said about the work contributed by successive inventors. 1. _Submersion._--We have seen that for submersion and return to the surface, Bourne had at the very beginning devised the side-tank to which water could be admitted, and from which it could be ‘blown out’ at will. Bushnell, a remarkable inventor of British-American birth, substituted a hand-pump in his boat of 1771, for the mechanism proposed by Bourne. In 1795, Armand-Maizière, a Frenchman, designed a steam submarine vessel to be worked by ‘a number of oars vibrating on the principle of a bird’s wing.’ Of these ‘wings,’ one lot were intended to make the boat submerge. Nothing came of this proposal, and for more than a century tanks and pumps remained the sole means of submersion. In 1893 Haydon, an American, invented a submarine for the peaceful purpose of exploring the ocean bed. Its most important feature was the method of submersion. This was accomplished by means of an interior cylindrical tank, with direct access to the sea, and fitted with two powerfully geared pistons. By simply drawing the pistons in, or pushing them out, the amount of water ballast could be nicely regulated, and the necessity for compressed air or other expellants was avoided. This device would have given great satisfaction to William Bourne, the Elizabethan gunner, whose original idea, after more than two centuries, it carried out successfully. Finally, in 1900, the American inventor, Simon Lake, in his _Argonaut II._, introduced a new method of diving. For the reduction of the vessel’s floatability he employed the usual tanks; but for ‘travelling’ between the surface and the bottom, he made use of ‘four big hydroplanes, two on each side, that steer the