Nordenfelt II. had two distinct conditions of existence as a torpedo craft—that of a surface boat and a submarine one. The sinking operations were as follows: the furnaces were hermetically closed, upon which combustion was soon brought to an end. The piece of funnel connecting the boiler with the outward portion was then removed and the doors placed in position. Whilst these changes were being effected, water was allowed to run into the ballast tanks to reduce the buoyancy to its proper limit, and this arrived at, nothing remained but to close up the conning tower and to set in motion the vertically acting screws to place the boat quite out of sight. In a paper which he read before the Royal United Service Institution, on February 5, 1886, Major-General Sir Andrew Clarke in the chair, Mr. Nordenfelt after mentioning previous under-water vessels, gave his views as to the reason of their failure. First of all he said they were always built too small and too weak. The longest was 45 feet, and their small dimensions and weak plates made them useless in bad weather and dangerous for submersion; the small air space available forced the crew to use chemical means to obtain pure air. Secondly, they were never made for firing a fish torpedo; consequently they had to endeavour to fix a mine to the bottom of a vessel, a feat which Mr. Nordenfelt considered impracticable, owing to the risk of contact with the vessel, which, especially if it were pitching or moving, might easily destroy the boat. Thirdly, in all the early boats, the mines were charged with only black powder, the effect of which was less destructive than that of the gun-cotton or dynamite in the fish torpedoes. The effect of the explosion, again, against a wooden ship, was nothing like as serious as against the thin bottom plates of an ironclad. Fourthly, all the boats hitherto in use were propelled by hand power; this gave too much hard work to the crew, who could not take the boat any distance on the surface previous to the actual attack, and made it quite impossible for it to face any rough weather. In the Nordenfelt boat the use of steam diminished the number of men, and they had so little to do when below the surface that the temperature, lower than in modern stokeholes, was no detriment. Fifthly, all previous boats had most unreliable means of descending and ascending. The descent by steering downwards in the American boats of the Civil War period was quite as dangerous as the attempts before and after that time to lower and raise the boats and to keep them steady at any desired depth, by means of increasing and decreasing the weight of the boats by more or less water-ballast or by altering their displacement.