The submarine torpedo-boat is to most people a complete mystery, and before describing the composition and strength of the submarine fleets at war it may therefore be of interest to say something of the principal features common to all types of submarine craft.
Method of Submergence
It may sound ridiculous, in face of the many accidents which have occurred, to say that one of the greatest difficulties is to make a submarine sink sufficiently quickly, and one of the easiest of operations to make her rise, and yet such is undeniably the case.[[1]]
It will be readily understood that any delay in disappearing beneath the surface when attacking would be a great danger to a submarine in action. For example, a number of hostile torpedo-boat destroyers are scouring the sea in advance of a fleet, and are discovered at daybreak by the submarines, which are waiting to attack the fleet behind, approaching at a speed of 30 knots an hour. A hurried dive beneath the surface is necessary if the waiting submarines would avoid detection, which would, in all probability, mean destruction by the quick-firing guns of the destroyers.
When a submarine is travelling on the surface she is in what is technically called the light condition, that is to say, with her water ballast tanks empty, but when it is required to sink her so that only the tiny platform, or deck, and conning-tower are above the surface, water is let into these ballast tanks, and the additional weight causes her to sink into the sea until her back is almost flush with the surface—this is known as the awash condition.
It is not difficult to perceive that when travelling awash, a wave might at any moment roll along the tiny unprotected deck of the submarine, break over the mouth of the conning-tower, and descend like a waterspout into the interior. Were this to happen a terrible disaster might result, for it must be remembered that when travelling awash, a very little additional weight would cause the submarine to plunge beneath the surface. In order to obviate this risk it has become a rule that when proceeding with this small margin of buoyancy, the hatch covering the mouth of the conning-tower should be screwed down and the submarine hermetically closed, ready to sink.
To many it may appear strange that total submergence is not accomplished by letting still more water into the ballast tanks, but entirely with the aid of the propellers and rudders. A submarine has two, and sometimes three, pairs of rudders; one pair of ordinary vertical ones to guide her to port or starboard, and a horizontal pair to cause her to dive and rise. Two additional fins are frequently placed on each side of the forepart of the vessel to assist the diving and rising.
In order to make the submarine dive beneath the surface, the horizontal rudders are deflected when the boat is proceeding at full speed. The action of the water against the rudders is such that the bows are forced down and the whole vessel slides under the surface. The principle is much the same as that of steering an ordinary surface vessel, where the force of the water against the rudder causes the vessel to swing to right or left.
From this it will be seen that a submarine is only held below the surface by the action of her rudders on the passing water; should the propellers driving her along cease to revolve and the vessel slow down, she automatically rises to the surface because the rudders have no longer any effect.
Although the steering both on the vertical and horizontal plane is controlled by hand, it would be quite beyond the strength of a man to move the various rudders as required, so electric motors are installed to perform the actual work. In fact, almost everything in a submarine is operated by electricity.