Now, before I explain how the submarine is made to dive and how the ballast tanks work, or, rather, the other way about, I want to tell you a little about the why and the wherefore of these very interesting operations.
The Four States of the Submarine.—A submarine has four states, or conditions, in which it exists in the water. These are (1) the light, or surface cruising condition; (2) the awash, or partly submerged condition; (3) the submerged condition; and (4) the totally submerged condition—all of which is clearly shown in the diagram [Fig. 26].
FIG. 26. HOW THE SUBMARINE SUBMERGES OR THE FOUR STATES OF THE SUBMARINE.
The Light Condition.—The light, or cruising, condition is simply the position a submarine takes when she floats on the water, due to her own natural buoyancy, and it is exactly like that of any other ship.
While in this position the captain takes his observations from the deck, if there is no danger of being hit by the enemy; but if there is danger, he then makes his observations through the ports from the inside of the conning tower.
The Awash Condition.—This condition is not as natural as the one just described, and it has to be done by means of the ballast tanks. These are located fore and aft and they can be connected with, or disconnected from, each other at will.
Now, when the captain wants to bring his submarine to the awash condition an inlet valve, or Kingston valve as it is called, is opened and the sea-water then flows into these tanks, the amount and velocity of the inrushing water being, of course, under control at all times.
This extra weight destroys part of the buoyancy of the boat, and as she gets heavier she sinks until nothing but her conning tower remains above the water-line, the deck being awash. While in this condition observations are taken either from the ports in the conning tower or with the periscope, the object-glass of which has been lowered enough to become useful.