The Submerged Condition.—In this condition the periscope alone remains above the water. It is had by allowing more water to flow into the ballast tanks, thus destroying a little more of the craft’s buoyancy, which makes her sink down until the conning tower is completely submerged. It is in this condition that the captain makes his observations with the periscope.
The Totally Submerged Condition.—This is an exaggeration of the submerged condition, and it is had by letting still more water flow into the ballast tanks, thus sinking the submarine completely. The only way to steer the boat when it is in this condition is, of course, by means of the compass, for both the conning tower and the periscope are totally submerged.
But do not mistake the term totally submerged to mean that the buoyancy of the submarine is totally destroyed; for such is not the case during any stage of its submergence. You can easily see that if the buoyancy were completely destroyed the submarine would then become a dead weight and sink to the bottom of the sea, never more to rise.
Instead, when the submarine is totally submerged she can, by what is known as her reserve, or extra buoyancy, and about which you will read later on, come to the awash or the light condition in a few minutes by simply pumping the water out of the ballast tanks.
FIG. 27. FORE DIVING HORIZONTAL RUDDERS OR HYDROPLANES OF A SUBMARINE.
How a Submarine Dives.—Now let’s get back to the way a submarine dives. In the first place, let us suppose the boat is running in the light, or cruising, condition. An enemy ship is sighted and the captain of the undersea craft gives orders to clear the deck and close the hatches. Then he brings the boat from the cruising to the awash condition, which is done as we have just described.
FIG. 28. HOW THE SUBMARINE DIVES.
Next, he gives the order to the man at the diving wheel to make the dive. He does not need to do this by word of mouth but he can use an electric indicator which points out the angle at which he wants the horizontal rudders set (see [Fig. 27]). Contrary, now, to what you might expect, a submarine cannot dive at any angle, but it must make a very shallow dive.