IV
To attack the submersible is a matter of opportunity. It is only when one is caught operating on the surface, or is forced to the surface by becoming entangled in nets, that the patrol has the chance to fire upon it. Against this method of attack, modern submersibles have been improving their defenses. To-day, they are shielded with armor of some weight on the superstructure and over part of the hull. They are also equipped with guns up to five inches in diameter, and, affording, as they do, a fairly steady base, they can outmatch in gun-play any of the lighter patrol boats which they may encounter.
One of the important improvements which have been made has resulted in the increased speed with which they now submerge from the condition of surface trim. A submersible of a thousand tons displacement will carry about five hundred tons of water ballast. The problem of submerging is mainly that of being able rapidly to fill the tanks. On account of the necessity of dealing with large quantities of water in the ballast system, the European submersibles are equipped with pumps which can handle eight tons of water per minute.
Again, the speed which the electrical propulsion system gives the vessel on the surface greatly increases the pressure which the diving rudders can exert in forcing the submersible under water. This effect may be so marked that it becomes excessive, and Sueter emphasizes the point that vessels at high speed, when moving under water, may, on account of the momentum attained, submerge to excessive depths. To eliminate this tendency, there is a hydrostatic safety system which automatically causes the discharge of water from the ballast-tank when dangerous pressures are reached, thus bringing the submersible to a higher level where the pressure on the hull will not be so severe. From this it follows that the opportunity of ramming a submersible, or of sinking it by gunfire, is greatly minimized, since the vessel can disappear so rapidly.
Copyright by Underwood & Underwood, N.Y.
INTERIOR OF A SUBMARINE[ToList]
A great deal has been attempted with nets. Fixed nets extend across many of the bodies of water around the British Isles. Their positions, doubtless, are now very well known to the Germans. The problem of cutting through them is not a difficult one. Moreover, the hull of the submersible has been modified so that the propellers are almost entirely shielded and incased in such a way that they will not foul the lines of a net. There has also been a steel hawser strung from the bow across the highest point of the vessel to the stern, so that the submersible can underrun a net without entangling the superstructure. Some nets are towed by surface vessels. The process is necessarily slow, and to be effective the surface vessel must know the exact location of the submersible. Towing torpedoes or high explosive charges behind moving vessels has been developed by the Italian Navy, but the chances of hitting a submersible with such devices are not very great.
Bomb-dropping from aëroplanes can be practiced successfully under exceptional conditions only. In view of the fact that such bomb-dropping is exceedingly inaccurate, and that the charges carried are relatively small, this form of attack ordinarily would not be very dangerous for the submersible. Surface craft have also employed large charges of high explosives, which are caused to detonate by hydrostatic pistons upon reaching a certain depth. Patrol boats carry such charges in order to overrun the submersible, drop the charges in its vicinity, and by the pressure of the underwater explosion crush its hull. Since the pressure of an underwater explosion diminishes rapidly as the distance increases from the point of detonation, it would be necessary to place the explosive charge fairly close to the hull of the submersible to be certain of its destruction. To accomplish this, it would seem that the ideal combination would be the control of an explosive carrier by radio energy directly from an aëroplane. Thus we would have a large explosive charge under water where it can most effectively injure the submersible, controlled by the guidance of an observer in the position best suited to watch the movements of the submerged target.
The third method by which to frustrate the attack of the submersible is to give better protection to the merchant marine itself. While a great deal of ingenuity is being concentrated on the problem of thwarting the submersible, but little common sense has been used. While endeavoring to devise intricate and ingenious mechanisms to sink the submersible, we overlook the simplest safeguards for our merchant vessels. To-day, the construction of the average ship is designed to conform to the insurance requirements. This does not mean in any way that the ship is so constructed as to be truly safe. Thousands of vessels that are plying the seas to-day are equipped with bulkheads that are absolutely useless because they do not extend high enough to prevent the water from running from one part of the ship to another when the ship is partially submerged. Then again, the pumping system is so arranged as to reach the water in the lower part of the hull when the ship is up by the head. Should the ship be injured in the forward part and sink by the head, these pumps would be unable to reach the incoming water before her condition had become desperate. There is a vessel operating from New York to-day worth approximately a million dollars, and if she were equipped with suitable pumps, which would cost about a thousand dollars, her safety would be increased about forty per cent. Her owners, however, prefer running the risk of losing her to expending a thousand dollars! If the merchant vessels were made more torpedo-proof, it would be an important discouragement to the U-boat commander. During the past two years of the war, nineteen battleships have been torpedoed, and out of this number only three have been sunk, showing that it is possible by proper construction to improve the hull of a ship to such an extent that it is almost torpedo-proof. While it may not be practicable, on account of the cost, to build merchant vessels along the lines of armed ships, nevertheless much could be done to improve their structural strength and safety; and since speed is an essential factor in circumventing torpedo attack, new cargo-carriers should be constructed to be as fast as is feasible.
So radically have conditions changed that to-day we have a superabundance of useless dreadnaught power. The smaller guns of some of these vessels, and their gun crews, would be far more useful on the merchant vessels than awaiting the far-off day when the German fleet shall venture forth again. The submersible must be driven below the surface by a superiority of gunfire on the part of the merchant marine and its patrols. In this way the submersible would be dependent upon the torpedo alone, a weapon of distinct limitations. In order to use it effectively, the submersible must be not more than from eight hundred to two thousand yards from its target, and must run submerged at reduced speed, thus greatly lessening its potentiality for destruction. To-day, submersibles are actually running down and destroying merchant vessels by gunfire. If merchant vessels carried two high-speed patrol launches equipped with three-inch guns of the Davis non-recoil type, and these vessels were lowered in the danger zone as a convoy to the ship, such a scheme would greatly lessen the enormous task of the present patrol. In the event of gunfire attack by a submersible, three vessels would be on the alert to answer her fire instead of one: an important factor in discouraging submersibles from surface attack!
The future of the submarine campaign is of vital importance. The prospect is not very cheerful. Laubeuf states that at the beginning of the war Germany had not over thirty-eight submersibles. This statement may be taken with a grain of salt; the Germans do not advertise what they have. It is probable, however, that to-day they have not more than two hundred submersibles in operation. Over four thousand patrol boats are operating against this relatively small number, and yet sinkings continue at an alarming rate. It is estimated that Germany will be able to produce a thousand submersibles in the coming year and man these vessels with crews from her blockaded ships. This will be a tremendous addition to the number she has now in operation. The greater the number of submersibles she has in action, the greater the area the submarine campaign will cover. The number of patrol vessels will have to be increased in direct proportion to the area of the submarine zone. Since a large number of patrol boats has to operate against each submersible, it will be seen that a tremendous fleet will have to be placed in commission to offset a thousand submersibles. Thus the problem becomes increasingly difficult, and the protection of the trade route will be no more thoroughly effected than it is to-day—unless we overwhelm the enemy by a tremendous fleet of destroyers.