Those who had little faith in the future of under-water warfare declared that a torpedo could never be fired from a tube in a submerged vessel without disastrous effects. The Nordenfelt boats were certainly not successful in discharging torpedoes, for as a general rule they as nearly as possible stood up vertically on their tails and proceeded to plunge to the bottom stern first on these occasions.
However, since then, submarines have fired torpedoes quite satisfactorily under water.
The expulsion of a torpedo from a vessel totally submerged in the water, whether equal to or less than the weight to the water displaced, naturally reduces her weight and tends to send her up towards the surface. This tendency can best be counteracted by the admission of a certain quantity of water ballast into the boat.
The method now usually followed is to allow the surrounding water to enter the tube immediately after the launch of the torpedo, and as the weight of the volume of water admitted will be about equal to that of the missile ejected, the longitudinal stability of the submarine should not be disturbed. When the second torpedo comes to be placed in the tube, the volume of water already in it must of necessity be ejected, and a compensating reservoir may be used to receive it. As each torpedo is fired a certain amount of water, corresponding to the weight of the projectile, must be allowed to enter the compensating reservoir. This may be done automatically.
The Engineer in a leader on January 18, 1901, said: “The discharge of a bow torpedo (by a submarine) would be instantly followed by the rise of the bow; relieved of the weight the boat would tend to stand on end. If going ahead at the time she would immediately come to the surface to be destroyed. If going astern she would plunge downwards and the consequences might be equally serious.... Torpedoes must be fired when the submarine is at rest.”
In spite of this dogma submarines have fired torpedoes whilst in motion with success, and in modern submarines ample provision is made for the loss of weight occasioned by the discharge of the torpedo.
4. Reference has been made to the fact that when the Nordenfelt boat was moving along on an even keel, and a greaser walked forward a couple of feet in his engine room, her head would go down a little, the water would surge forward in the tanks, and she would plunge to the bottom, unless checked in time. It has been said that one man going forward in a submarine boat would cause her to dive to a depth of thirty-six feet in one minute. The movements of the crew may be compensated for by automatic arrangements, but the ideal method would be one in which every one remained immovable at his post during the submerged run.
Steering Below Water.
Quite early in the history of submarine navigation it was found that the compass was not so reliable when the boat was navigating under water as it was when she was on the surface. This is not to be wondered at, for the compass of a submarine is placed in the interior of a tightly-closed metallic shell and in close proximity to an electro-motor and powerful currents capable of influencing it considerably, if not of rendering it altogether useless.
The principal causes of the unreliability of the compass on a submerged boat are:—