The distance of vision varies somewhat under water, as we look out from the side windows cut into the steel armor of the commander's conning tower. We can naturally see farther in the clear water of the deep ocean than in the turbid, dirty water at the mouth of a river, and the surface of the water-bottom has a direct influence on the sight, which is far more distinct over a light sand than over dark seaweed or black rocks, and at an upper level the sunshine is noticeable many meters under water. But in any case, the vision underseas is of the shortest, and does not extend beyond a few meters; light objects and even the stem and stern of our own boat are invisible from the turret. We are unaware, therefore, of advancing ships, derelicts, or projecting rocks, and no lookout can preserve us from these dangers.
The crew is entirely ignorant of their surroundings. Only the commander in his turret surveys through the periscope now and then a small sector of the horizon; and in turning round the periscope he gradually perceives the entire horizon. But this survey demands great physical exertion, which on a long cruise is most fatiguing. The periscopes erected through the upper cover of the turret must not be too easily turned in their sockets, and the latter are very tightly screwed in, for otherwise they would not be able to resist the water pressure at a great depth. The effort of simply turning the periscope is so exhausting that casual observations of the horizon are made by the officer of the watch; but during naval maneuvers or in time of war, the commander alone manipulates the periscope. It is essential in this case that the periscope should not arise needlessly above water and betray the presence of the U-boat.
The commander must possess the absolute confidence of his crew, for their lives are in his hands. In this small and carefully selected company, each man, from the commanding officer down to the sailor boy and down to the stoker, knows that each one is serving in his own appointed place, and they perform their duties serenely and efficiently.
I have always allowed every man on board once, in turn, to have a look through the periscope; it is their highest ambition, and the result is excellent, for it reassures them and they feel more confident as to their own safety after the granting of this small favor.
As we advance underseas, unless passing through a school of fish, we seldom see any fish, for the noise of the propellers frightens them away; but when we lie at rest on the bottom of the ocean, the electric lights allure them, and they come and stare at us with goggling eyes close to the windows in the turret.
The life, therefore, in our "cylinder" as we call it, offers a good deal of variety. The term "cylinder" is exact, for the inner conformation of a submarine is necessarily rounded, so that relatively thin partitions can successfully resist the greatest pressure of water.