Submarines, Mines and Torpedoes in the War

by Charles W. Domville-Fife

In the earlier types of submarine boats, a considerable time was required to open the valves and allow sufficient water to enter the ballast tanks to make them sink to the awash condition. Some of the now obsolete French naval boats took as long as fifteen to twenty minutes to carry out this simple operation. The main reason for this was, that they were designed with too much surface buoyancy, that is to say, they rode too high in the water when floating in the light condition compared with the inadequate means then employed for the inlet of water into the ballast tanks, and were thus forced to let in an enormous quantity of water at a very slow rate before they settled down sufficiently to enable total submergence to be accomplished by the use of the horizontal fins and rudders. This great drawback has now been completely overcome, and the modern submarine can sink below the surface in about three minutes.

When water is pumped into the ballast tanks in order to make the submarine settle down, the air which normally fills these tanks is compressed into a fraction of its proper space, and is therefore always exerting a downward pressure which increases as more water is pumped in. Therefore, when it is desired to bring the submarine to the surface again, all that is necessary is to open the valves and allow the compressed air to force the water out. It should, however, be remembered that there is really no need to “blow out” the ballast tanks in order to bring the submarine to the surface, for this can be much quicker accomplished by simply elevating the horizontal rudders; but in this case the submarine only rises just above the surface—to the awash condition—whereas if the tanks are emptied of water she rises to the light or cruising condition. This substantiates the assertion made at the beginning of this chapter—that it is far more difficult to make a submarine sink than it is to make her rise.

It has been said that a man walking from one end of a submarine to the other would, in all probability, cause her to plunge dangerously, so delicate is the state of equipoise when totally submerged. Whatever may have been the case in the early types it is certainly not so now. So steady are modern submarines when running below the surface, especially those of the British, Russian, French, and Japanese and German Navies, that the long up and down hill glides, which, with some boats, used to amount to yaws of from 20 to 30 feet, have now been reduced to a few feet in so many hundreds of yards. In fact, this switch-back motion is almost unnoticeable except when the submarine is being swung round at a sharp angle. In no case, however, is it sufficient materially to affect the firing of the torpedoes.

The reserve buoyancy of a submarine in the awash condition—or diving-trim, as it is called in the British flotillas—is necessarily very small, amounting to little more than two or three pounds in a thousand, which in a 300-ton vessel means a difference of only about 100 gallons of sea-water between the ability to float and the inevitability of sinking. Any material increase in the small margin of what is known as positive-buoyancy must be accompanied by a corresponding increase in the power of propulsion, otherwise it would be quite impossible to drive her under, or, in other words, to overcome the vessel’s natural tendency to float on the surface.

For these and other reasons, a submarine when running submerged is in such a delicate state of equipoise that any sudden increase or loss of weight would upset the balance and so cause the vessel to either dive or rise with dangerous rapidity.

This would be the effect produced when a torpedo was discharged were provision not made to counter-balance this sudden loss of weight by means of compensating-tanks, into which sufficient water is pumped to compensate for the loss of weight incurred by the discharge of each torpedo.

Many submarines are also fitted with bow and stern trimming-tanks, into which water can be pumped in such a manner as to correct any tendency of the vessel to float too high or low at either extremity.

Propulsion.

Of the many complicated problems surrounding submarine boat construction the motive power and propelling engines have been in the past, and are still, the most profound puzzles. Steam, compressed air, electricity, petrol, and heavy oil have all been used with varying results since first this type of vessel came into being; and many curious engines for using these prime movers in conjunction with each other and with chemical compounds have been evolved by ingenious inventors.

About steam and compressed air little need be said, for although given a good trial, especially by the French naval authorities, they were abandoned some years ago in favour of a combination of petrol and electric engines, which in turn have given place to more powerful machines using heavy oil and electricity. Steam is, however, again being used in conjunction with turbine engines for surface propulsion.