It was propelled by a 15 h.p. petroleum engine of the Brayton type; as armament a submarine cannon, 11 feet long and 9 inches in diameter, was carried, and the projectile was expelled by means of a charge of compressed air. “She was the first submarine since Bushnell’s time,” writes Admiral Hichborn, “employing water ballast and always retaining buoyancy, in which provision was made to ensure a fixed centre of gravity and a fixed absolute weight. Moreover, she was the first buoyant submarine to be steered down and up inclines in the vertical plane by horizontal rudder action, as she was pushed forward by her motor, instead of being pushed up and down by vertically acting mechanism. Her petroleum engine, provided for motive power and for charging her compressed air flasks, was inefficient, and the boat therefore failed as a practical craft; but in her were demonstrated all the chief principles of successful brain-directed submarine navigation. After the completion of the boat, Holland led the world far and away in the solution of submarine problems, and for a couple of years demonstrated that he could perfectly control his craft in the vertical plane. Eventually, through financial complications, she was taken to New Haven, where she now is.” In 1896 her air-compressor was removed to work a forge, and she is now nothing but an empty hull. _Holland No. 4_ was constructed in the yard of Gammon and Cooper, of Jersey City. It was simply meant as a model, being only 16 ft. 4 in. long, 28 in. in diameter, and displacing a ton. The motor was an explosive engine, which was to serve for propulsion above and below the surface. The life of this model was unfortunately short, for on one occasion she was submerged with her cupola open, with the result that the water entered and she sank. _Holland No. 5_, commonly known under the name of the “Zalinsky Boat,” owing to its dynamite guns, was built at Fort Lafayette. It was— 30 feet long, 7 feet beam, 7 feet in diameter, and was armed with two Zalinsky pneumatic dynamite guns. Owing to an error in construction, she was shipwrecked on the rocks, but was afterwards rescued and used for some experiments in the docks. _Holland No. 6_ never got further than the design stage; it was not a true submarine, not being capable of total submergence. _Holland No. 7_ was known as the _Plunger_. [Illustration: BOW VIEW OF THE “HOLLAND.” ]