that they had become possessed of types of submarines and submersibles upon which dependence could be placed in time of war for destroying an enemy’s vessels, the British Admiralty abandoned the attitude of scepticism and watchfulness combined it had maintained for so long, and ordered five boats from the Holland Company for experimental purposes. The experiments which were made with these boats resulted in the Government becoming possessors of what were known as the A class of submarine. [Illustration: BRITISH SUBMARINE A13. _Photograph by E. Sankey, Barrow._] [Illustration: BRITISH SUBMARINE C22. _Photograph by E. Sankey, Barrow._] Very little has been revealed of the details of modern submarines, for if there is one subject more than another upon which the admiralties of the world are agreed, it is that they should not let one another know the secrets of the mechanism of these under-water craft. That, at least, is the theory, but it is very questionable if all the governments are not quite well informed as to the constructional details of each other’s submarines, and probably know almost as much about them as they do about their own. The experiments at Barrow and elsewhere with the Holland boats and their successors have been responsible for the introduction of several classes of submarines, every one of which embodies improvements upon its predecessor. The five boats built for Great Britain at Barrow, in 1902, were 63 feet 4 inches in length by 11 feet 9 inches breadth, by 12 feet 1 inch depth, and had a surface speed of ten knots and a submerged speed of seven knots. The A class, which appeared in 1902, began with a vessel of 180 tons displacement, and 100 feet in length by 12 feet 8 inches beam. Larger vessels of this class were built from 1904 to 1907 of 204 tons displacement, but varying considerably in dimensions. The B class of 313 tons submerged displacement was introduced in 1903-4. These vessels were 135 feet by 13 feet 6 inches, and had a cruising speed of fourteen knots and a submerged speed of nine knots. The C class, which resembled the B class in many particulars, appeared in 1906-7, as did also the D class, but the latter were of 500 tons submerged displacement and of fifteen knots cruising speed. The five boats built on the Holland designs were each propelled by a 4-cylinder 190 h.p. petrol engine besides an electrical engine of 70 h.p. The armament was an 18-inch torpedo tube in the bow, and each carried five torpedoes. These vessels were divided into seven compartments. The deck was 31 feet 4 inches by 4 feet 5 inches. There were two diving rudders at the stern, and the conning tower, of 32 inches diameter, was formed of 4-inch armour. The A type, the first of which sank in March, 1904, off Spithead, had a 12-cylinder 600 h.p. gasolene engine. The B type had engines of 850 h.p., and could carry 15 tons of fuel structurally, and were provided with a forward superstructure. The D type have heavy oil