In 1864, during the American civil war, a submarine boat succeeded in sinking the Federal frigate _Housatonic_. This boat, however, was hardly an unqualified success, as, running into the hole made by its torpedo, it went down with the ship; and three crews had previously been lost while carrying out its initial experiments. Since then, many methods of submersion have been tried; but it is only within recent years that naval powers have awakened to the fact that a submersible boat, though by no means so formidable for offensive purposes as its name at first leads one to believe, is a factor which might have to be taken into consideration in the next naval war.
Modern types of these boats are the Holland, Nordenfelt, Tuck, and Goubet. The Holland boat comes to us from over the Atlantic, and is peculiar in its weapon of offence. It is fifty feet long, eight feet in diameter, and is driven by a petroleum engine carrying sufficient fuel for two days' run. The diving is effected by means of two horizontal rudders, one on each side of the stern. This only allows of submersion when the boat is in motion; and the boat cannot be horizontal while submerged. It carries ten-inch gelatine blasting shells, fired from a pneumatic gun twenty feet long, whose radius of action is two hundred yards under water and one thousand yards above. The use of gelatine is also objectionable, as the confined space and the vibration of the boat prevent such explosives being carried without some risk of premature explosion. It is for this reason that gun-cotton is adopted in torpedo work, as it will not explode on concussion, and is little affected by change of temperature.
The principal features of the Nordenfelt boat are its method of submersion and its propulsion by steam. The boat is one hundred and twenty-five feet long, twelve feet beam, and displaces two hundred and fifty tons when entirely submerged, one hundred and sixty tons when running on the surface. Her propelling machinery consists of two double cylinder compound engines, with a horse-power of one thousand, and propelling the boat at fifteen knots on the surface. The submersion of the boat is effected by means of two horizontal propellers working in wells at each end. Two conning-towers project about two feet above the deck, of one-inch steel, surmounted by glass domes, protected with steel bars, for purposes of observation. The boat usually runs on the surface with these towers showing, unless the buoyancy, which is never less than half a ton, is overcome by the horizontal propellers, when the boat becomes partially or totally submerged according to their speed. To ascend to the surface it is only necessary to stop the horizontal propellers, which also stop automatically on reaching a set depth. In the forward tower are the firing keys, machinery and valves necessary for driving or steering the vessel, for controlling the horizontal propellers, and for discharging the Whitehead torpedoes. Four of these are carried, and they are discharged with powder from two tubes in the bows. In the conning-tower are also placed the instruments indicating the depth, level, and course. When the boat is awash, the funnels have to be unshipped and the boat closed up before submersion. The length of time, twenty-five minutes, required for this operation is an objection to this boat, though when submerged it does not get unpleasantly hot. The temperature after a three hours' submerged run was only ninety degrees Fahrenheit. The crew consists of a captain and eight men.