These various compartments are: (1) the conning tower; (2) the navigating compartment; (3) the engine and dynamo room; (4) the fore and aft storage battery rooms; (5) the fuel tanks; (6) the diving control compartment; (7) the fore and aft ballast tanks; (8) the water pumps; (9) the fore and aft high pressure air flasks; (10) the high pressure air compressor; (11) the torpedo compartment; (12) the mine compartment; (13) the trimming tanks; (14) the quarters of the crew; and (15) the quarters of the officers. All of these are clearly shown in Fig. 25.
The watertight doors of these compartments are worked by _worm_ gears, driven by electric motors, as shown in Fig. 25, and any of the doors can be opened or shut by merely throwing a switch.
=A Peep into the Conning Tower.=—The free space inside of the conning tower is not more than 8 feet in height and 10 feet in diameter.
Sticking down through the deck for about 2½ feet is the periscope, or two of them, for all submarines now built are fitted with a pair of them so that should one of them be hit and put out of business the other will be available.
[Illustration: FIG. 25. THE MAIN PARTS OF A SUBMARINE.]
This instrument is formed of a long tube with a hood at the upper end, which is outside of the conning tower, and an elbow at the lower end, inside of the tower. An eye-piece is fixed to the lower end, so that the captain can scan the horizon at all times. How a periscope is made and used will be described in a later chapter.
Just below the eye-piece of the periscope is the underwater steering wheel, and close to and to one side of the latter is the underwater compass. In the more recent submarines a _gyroscopic compass_[17] is used as well as the regular magnetic compass because the gyroscopic compass is not affected by stray magnetic lines of force. Besides, a _gyro_ compass, as it is called for short, points to the true north instead of to the magnetic north pole, and a true compass is of the greatest importance in guiding the submarine at night or when it is submerged, for it is then as blind as the fish in Mammoth Cave.
Around the inside of the tower near the bridge are placed _ports_ through which the captain makes and takes his observation when the boat is afloat. Within easy reach of his mouth are _speaking tubes_ which lead to the engine, diving, and torpedo compartments. The captain also has at his finger-ends an electric signal system of lights and bells, which he operates by push buttons and switches.