When Mr. Nordenfelt built his boats electric accumulators were very much inferior to those of to-day; no designer of an under-water vessel would think nowadays of using the steam given off by heated water for under-water propulsion. As to his theory that a submarine boat must always descend on an even keel, this has since proved to be entirely erroneous; the modern diving torpedo boat goes down at an angle and is brought to the horizontal position at the required depth either automatically or by hand-worked mechanism. [Illustration: “NORDENFELT II.” AT CONSTANTINOPLE. ] During her trials _Nordenfelt I._ hardly did herself justice, but nevertheless in the beginning of 1886, she was bought by the Greek Government, and in April, 1886, trials took place in the Bay of Salamis, when Mr. Nordenfelt’s agent carried out the various conditions imposed. Shortly after the first boat had been bought by Greece, Turkey ordered two submarine boats (_Nordenfelt II._ and _III._) from the inventor. Both boats were sent to Turkey in sections, but only one was assembled and tested. In 1887 it underwent trials at Constantinople, which were witnessed by the Sultan himself, who expressed himself highly satisfied with the performance of the boat. [Sidenote: Nordenfelt IV.] Mr. Nordenfelt’s fourth vessel was built by the Barrow Ship Building Company, the machinery being supplied by Messrs. Plenty & Sons, Newbury. The principal dimensions were: Length, 125 feet; diameter, 12 feet; displacement fully immersed, 245 tons; in light surface condition, 160 tons. The engines turning the main propeller were especially designed for using steam at varying pressures, and indicated 1,000 h.p. when working with steam at a pressure of 150 lbs. At that power her estimated speed was 15 knots. Submerged, her speed was 5 knots. Fourteen auxiliary engines were carried for driving air circulating and feed pumps for steering and sinking. In the middle was the entrance to the stokehole through a scuttle 4 feet in diameter. Fore and aft of this scuttle were two funnels, and about 30 feet from the stem and stern of the boat were the conning towers, 2 feet high and of the same diameter. They were of 1–inch steel and were considered perfectly impervious to any shot which in warfare would ever be directed against them. In the forward tower were placed at the hands of a commander means of controlling every motion of the vessel. The boat was divided into five compartments: (1) The torpedo chamber containing two tubes; (2) Quarters for four officers; (3) The boiler room; (4) The engine room; (5) The men’s quarters, cooking galley, stoves, &c. The crew consisted of nine men all told; 35 tons of cold water were carried in the tanks; and 27 tons of hot water in the boilers. These latter were expected to store sufficient heat for a run of 20 knots under water. The coal bunkers held stores of coal