How much water then must we take in? The answer to this question is a matter of instinct, education, and experience and we must also depend on the cleverly devised apparatus made for this purpose.
The submarine like the airplane must be always maintained at the proper level. The weight of the boat varies continually during a prolonged voyage. Food is devoured and the diving material of the machinery is consumed. The water in which the boat swims continually changes weight and the boat is imperceptibly raised or lowered in a way very difficult to ascertain. The officer responsible for the flooding of the submarine must painstakingly keep its weight under control during the entire navigation. The weight of a meal eaten by each man of the crew, the remains of the food and the boxes in which it was contained, which have been thrown overboard, must be calculated as well as the weight of the water, and the officer employs delicate apparatus for these measurements.
On the open seas these alterations in weight do not occur very rapidly; but whenever a boat approaches the mouth of a river, then the transition from salt to fresh water happens very suddenly and may provoke the undesirable disturbances to which we have already alluded. Also warm and cold currents at different depths produce thermotic conditions, which surprisingly change the weight of the water.
Peculiar as it may appear, a submarine must be lightened to descend to a very great depth, whereas, in steering to a higher level, more water must be admitted into the tanks to prevent our emerging to the surface with too great suddenness. This demands careful attention, skill, and experience.
The principal condition for the success of a submarine attack is to steer to the exact depth required. The periscope must not rise too far above water, for it might easily be observed by the enemy; but if, by clumsy steering, the top of the periscope descends below the waves, then it becomes impossible to take aim to fire the torpedo. The commander therefore must be able to depend on the two men who control the vertical and horizontal rudders, whom another officer constantly directs and supervises.
When the boat has reached the prescribed depth a close examination is made of all the outward-leading pipes, to see if they can properly resist the water pressure; if any tiny leak has been sprung, every cap must be tightly screwed down; for it is evident it would be very undesirable if any leak should occur and increase the heaviness of the submarine. Absolute silence must prevail so that any dripping or greater influx in the tanks can be observed.
Quietly and silently the boat advances against the enemy; the only audible sounds are the purring of the electric motors and the unavoidable noise made by the manipulation of the vertical and horizontal rudders. Alert and speechless, every man on board awaits a sign from the commander, who is watching in the turret; but some time may elapse—now that the periscope is lowered and nearly on the level of the waters—before the adversary becomes visible again. The ship may have changed her course and have taken an opposite direction to the one she was following at the moment we submerged. In that case she would be out of reach and all our preparations prove useless.
At various intervals, the commander presses an electric button and raises and lowers the periscope as quickly as possible, so as to take his own observation without, if possible, being observed himself; for he knows that any injury to the periscope—his most priceless jewel—would, as it were, render the boat blind and rob him of the much coveted laurel leaves. During these short glimpses the commander only perceives a little sky and the wide, round plate of the reflected sea with its dancing waves, while the nervous tension of the expectant crew increases every minute.
At last is heard a joyous outcry from the commander, "The fellows are coming!"—and after one quick glance, to locate the enemy exactly, the periscope is lowered. Now every heart beats with happy anticipation and every nerve quivers with excitement. The captain quickly issues his orders for the course to be steered and for the necessary navigation. The officer in charge of the torpedoes receives the command to clear the loaded torpedo for firing, while the captain quietly calculates, first, the relative position of his boat to the enemy's ship, according to the course she has taken; secondly, at which point he must aim the torpedo to take surest effect, and—in the same way as in hunting a hare—he withholds the shot to correspond to his victim's gait.
Many thoughts fly through his brain. Here, among his companions, the annihilation of the enemy will cause joyful enthusiasm, while among them their downfall will cause overwhelming sorrow. But without doubt they must vanish from the seas, and only a man, who has experienced these sensations, knows how many secondary matters occur to him at such a time.