The submarine is essentially a torpedo vessel, launching its torpedoes when submerged and unseen. The size of the torpedo and number of discharge tubes have gradually in creased, the usual armament at present being the 21 inch torpedo, the largest conveniently manhandled, with four tubes at the bow and two at the stern. The tubes are horizontal and fore and aft, the breech ends being inside the pressure hull, loading and other operations being readily effected when submerged. Two torpedoes for each tube is the usual complement, one being stowed in the tube and the other in the torpedo room. Each tube has a water tight cover at either end, the inboard cover being opened and closed in the torpedo room, whilst that outboard—the cap—is operated by gearing from the room. The apertures for discharge in the bow are fitted with shutters which open and close with the caps, and when closed give a fair form to the bow to reduce resistance. The torpedoes are discharged by air pressure, either from the control room by the commander or at the tubes at his orders. The French are partial to revolving tubes fitted in the superstructure and trained by mechanism from the interior of the vessel. Such tubes are lighter than the ordinary tube, but have the disadvantage that they can only be loaded on the surface.
Previous to 1914 a few submarines carried a small gun of the disappearing type stowed in the superstructure. By the end of 1918 guns were fitted in all classes, the calibre having gradually increased, the limit being reached in the British "M" Class with one 12 inch. B.L. gun, the largest German submarine having two 15o mm. Against merchantmen the gun with a large number of rounds was more effectual than the relatively small number of torpedoes which could be carried. A 4 or 5 inch gun is now mounted in all classes, and although it is recognized that in a gun duel with an ordinary warship the submarine is at a great disad vantage, the gun may prove useful against weaker vessels or air craft. The guns are mounted on the superstructure in the open, reducing the submerged speed and endurance.
During the War the submarine was utilised for a purpose not previously suggested, but for which it proved particularly useful, viz.:—minelaying. Two types were developed by the Germans, the short range and the distant minelayer. The former were rela tively small—i70 to 500 tons—with six almost vertical tubes, open at top and bottom to the sea, passing through the pressure hull at the middle line forward of the conning tower. Three mines, one above the other, were stowed per tube, each held in position by stops which could be withdrawn, thus releasing the mines. The distant type were of 1,070 tons with a large compartment at the stern for stowing 42 mines. Two horizontal tubes with water-tight doors at both ends were used for discharging each tube taking three mines in line at a time, these being forced out of the tubes by two motors, one to each tube, which drove a number of spur wheels gearing with racks on the mine sinkers. Two apertures in the stern below the outer doors allowed the mines to fall into the sea abaft the propellers. In the short-range type of minelayer
the mines were inaccessible of ter insertion in the tubes and were always in sea water, whilst in the other type they were dry and accessible for examination and adjustment until loaded into the tubes. The two are also termed "wet" and "dry" types.
Bow torpedo tubes and guns were fitted in both types, but to provide for the space and weight of mines and tubes, the power of the engines and motors, and with it the surface and submerged speeds, were reduced as compared with the ordinary submarine. A few mine-laying submarines are attached to all navies, the largest being V-4 of the U.S. Navy, of 2,890 tons, carrying 6o mines and arranged with a mine room and tubes at the stern.
Up to 1914 submarines were divided into two main classes or types, the general service or patrol, and the coastal. The former was of 600 to Boo tons surface displacement with good speed and endurance, and capable of detached duties at some distance from its base, whilst the coastal submarine was of 250 to 400 tons, intended primarily for the defence of naval ports and bases. During the war other types were introduced, amongst which were the following :—Fleet submarine, with a surface speed of 24 knots, to accompany the fleets, and of which the British "K" class was the only example ; the cruiser submarine with good torpedo and a relatively powerful gun armament (2-15o mm.) of great endurance (18,000 miles at 8 knots), capable of detached service in distant seas, but too large and unhandy for ordinary duties, of which the German "U.14o" class of 1,93o tons was the first ; the minelayer submarine already referred to ; the monitor submarine, of which the British "M" Class was the only example, mounting a large calibre gun arranged for rapid fire when surfacing, and which at short range was sufficient to cripple unarmoured war ships; and the submarine-destroyer submarine with high sub merged speed (14 to 15 knots), which, sighting an enemy subma rine on the surface, would close with her at top speed submerged, and sink her before she could submerge, the only example being the British "R" Class. In addition to these, the Germans built the commercial submarine—the "Bremen" class—which was not a success. Several of these new types have disappeared or are not being repeated. A study of the submarines under construction by the naval powers indicates three distinct types. The most nu merous is the general service type with good surface and sub merged speeds, high endurance and excellent seagoing qualities, with strong torpedo armament, but mounting one gun of 4 or 5 inches calibre, and of displacement from 90o to 1,800 tons. Few cruiser submarines are being built, almost the only example being the British "X.1" with an average torpedo armament, but with a powerful gun armament of four 5.2 inch guns. The third type is the minelaying submarine, of which the number is small compared with the general service type. (W. J. B.)