Mr. Nordenfelt recognised that for the defence of open coasts and for operations where it might be necessary to keep the sea for days together without being able to seek the shelter of inlets or the mouths of rivers, other and larger proportions than those of his first 64 foot-boat would be desirable. He accordingly constructed a boat on such larger lines, the details of which are as follows:— Length 100 feet, beam 12 feet, displacement 160 tons, speed on measured mile 12 knots, distance travelled without re-coaling 900 miles, depth to which descent could safely be made, about 50 feet. Engines, surface condensing compound type, with two cylinders, and cranks at 90°, and at a pressure of 100 lbs. of steam indicating 250 h.p. Boiler, of the ordinary marine return tube type, having two furnaces; about 750 square feet of heating surface. Hot-water cistern, rhomboidal in body with spherical ends. Both boiler and cistern made for a working pressure of 150 lbs. per square inch. Armament, two fish torpedoes, 14 feet long, carried outside on the bow and discharged mechanically. Two Nordenfelt quick-firing machine guns consisting of 1–inch calibre. Sinking apparatus, two _vertical_ propellers, driven by two engines, each indicating 6 h.p.; these propellers were placed in the fore and aft line. This was an improvement on the earlier boat whose screws were fitted in side sponsons. The mere arrest of these propellers sufficed to bring the boat to the surface, as it had a reserve buoyancy. Bow fins, whose action was both automatic and controllable, maintained the boat in the horizontal position. The main propeller was placed abaft the rudder. Two main cold-water cisterns placed at each end, and containing 15 tons of water each, also one in centre of boat for regulating buoyancy containing 7 tons; coal bunkers on the side of boiler; 8 tons of coal carried at the side of hot-water cistern and in middle of boat. Crew, three men in a watch: two watches carried. With coal in the bunkers only, this boat could keep the sea for five days or more. No attempt was made to purify the air when submerged. When descending, the boat was perfectly horizontal, and was invariably kept so when moving under water by means of the bow rudders operated by a plumb weight. [Illustration: “NORDENFELT II.” RUNNING AWASH. ]