Vision When Submerged.
Perhaps the greatest difficulty which has beset both submarine construction and navigation is the puzzle how to see when submerged. This is now accomplished by means of periscopes, or tubes extending up from the roof of the submarine to a height of several feet above the surface—not unlike hollow masts. By a series of lenses and reflectors a picture of the surface is thrown down these tubes on to reflectors inside the submarine. A man with his eyes at the bottom of a periscope can see the surface clearly. Although it projects above the surface when the whole submarine is submerged, it is far too small an object to be easily seen moving through the water, and extremely difficult to hit by gun-fire.
The latest panoramic periscope—two of which are fitted in modern submarines—has a field of vision of about 60 degrees. The range of vision is, however, very short, owing to the periscopic tube projecting only a few feet above the surface. On a moderately smooth and fairly clear day steering by periscope is not altogether difficult, but at night or in fog this instrument is useless, and for this reason it would be almost impossible for a submarine to effect a submerged attack on an enemy at night. Hence the name given to this type of craft—daylight torpedo-boats—for in the brilliant light of day, when any attempt by ordinary torpedo craft to get sufficiently close to hostile warships to discharge a torpedo with reasonable hope of success would be foredoomed to failure, there is every possibility that submarines would effect a surprise attack.
Armament.
The chief armament of all naval submarines is the torpedo, which is expelled by a blast of compressed air from one of the tubes fitted in the bow and stern. Several torpedoes are usually carried by each boat, so that if one failed to strike the object of attack further attempts can be made.
About the efficiency of torpedoes nothing need be said here, for they now form an important weapon in every navy, and to this subject a future chapter is devoted.
The latest submarines built are also fitted with quick-firing guns for use when these vessels are cruising on the surface. The guns are arranged so that when it is desired to sink they can be made to disappear beneath the narrow deck of the submarine. The provision of guns has been made with the object of giving these vessels a means of defence should they be discovered by prowling hostile torpedo-boat destroyers, or by air-craft.
Habitability.
Many people imagine the interior of a submarine to resemble a stokehold, hot, stifling, and semi-dark, whereas the exact contrary is the truth. The temperature is but little above the normal for a ship’s engine-room, the air-supply is amply sufficient, and the whole interior is well illuminated by electric lamps.
The necessary supply of pure air is derived either from large steel cylinders containing the air in a highly compressed state or from flasks of oxylithe. The carbonic acid gas of the respired air being at the same time chemically absorbed.