As we told you in the first chapter, there are two kinds of undersea boats. These are (1) the Holland, or submarine type, and (2) the Lake, or submersible type. Now, the Holland boat has a shape very much like a cat-fish—that is, it has a blunt round head—and hence it can dive easily; while the Lake is shaped more like an ordinary boat and has a large superstructure, as that part above the hull[16] is called, and this makes it easier for the Lake to submerge—that is, sink on an even keel.
As the art of undersea boat building moved on apace, the two kinds of craft began to lose their original distinctive features and were merged into a single type. This was done to get a boat that was as strong and as speedy as and could dive like the Holland, and to have at the same time a boat that was as fast and as seaworthy on the surface as the Lake.
This is the reason that most of the undersea craft of to-day are a cross between the two kinds. In the older boats, though, the difference is still marked; but the machinery of both is just about the same, and consequently what we shall tell you of one is just as true of the other, and from now on we shall call both kinds simply submarines.
The Parts of a Submarine.—To begin with, a submarine is formed of: (1) the hull; (2) the superstructure, which is built on the hull; (3) the steering apparatus, which includes the submerging and diving devices; (4) the power plant, which consists of the engines, the dynamo-motors, and the storage batteries, all of which drive the submarine when it is on the surface and under the water-line.
As the power plant is a most important part of the anatomy of a submarine, it will need a whole chapter to describe it the right way, and this will come next. Now I’ll start in and tell you about the other parts of the submarine.
How the Hull Is Made.—The hull is made of thin but very strong sheets of steel riveted together. As the pressure of the water on it amounts to 187 pounds to the square inch, at a depth of 300 feet, it must be well braced or else there would be the unpleasant possibility that it might be crushed in. As a rule, though, a submarine never travels at a depth much greater than 100 feet.
Now, there are really two classes of submarines: (a) those that are built for coast patrol cruising, and (b) those that are built for trans-oceanic going.
A submarine of the first kind seldom has rough weather to contend with, and so she need not be built as strong as one that is designed for ocean going. She also has a slightly different shape from the latter, in that she has a round cross-section, as shown in Fig. 23.
By looking at Fig. 24 you will see that the ocean-going submarine is more nearly half-round; this tends to prevent her from rolling unduly. She also has a double hull which is divided into watertight compartments to protect her from sinking should an enemy ship ram or fire on her. The compartments are used as stowage tanks for fuel, etc., and so the space between the inner and outer skins, as the hulls are called, is not wasted.
A large number of fittings are fixed to the hull, such as the diving and steering rudders (all of which will be described later), while the superstructure is built on top of it.
What the Superstructure Is.—The superstructure consists of (1) the deck and (2) the conning tower. In the Holland submarine the deck is only about one-third as long as the boat and this allows it to dive easily.
The Lake boat is decked over nearly the whole length of the hull. In it are fitted rapid-fire guns which disappear, and there are watertight ventilators which let in fresh air when the boat is traveling on the surface. Further there is a hatch—that is, an opening in the deck with a watertight door—through which the torpedoes can be lowered into the hold of the submarine.
The Outside of the Conning Tower.—From out of the center of the deck rises the conning tower. This is a heavily armored, shell-proof, circular structure, from which the captain makes his observations and sends his orders down into the engine-room and controlling compartments. On the bridge or upper deck of the conning tower is a hatch by which the crew can get into and out of the boat.
A steering wheel and compass are fixed to the outside of the conning tower, and the submarine can be steered by these when it is running on the surface. A stanchion for carrying the signal lights is also secured to the conning tower; while the periscope, or eye of the submarine, passes through the bridge and to one side of the hatch. Of this wonderful instrument we shall have much to say a little further on.
Wires, or stays, as they are called, fore and aft are used to brace and hold the periscope and signal stanchion firm against the force of the water which presses on them when the craft is submerged and under way. The tops of the signal stanchion and the periscope are also braced by a signal halyard, which is simply a wire, or cable, stretched taut between them.
On all modern submarines a wireless aerial is attached to a mast which can be folded down flat on the deck when the submarine is getting ready to make a dive.
A Look Inside of the Hull.—Now let’s take a look inside of the submarine. The whole hull is divided up into a number of watertight compartments, any one of which can be shut off from the others and so lessen the danger of sinking by ramming or by shell-fire, should the boat be afloat. In these compartments are placed all the machinery and the controls for operating the submarine.
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.
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.
So you see he can get into instant touch with all the vital parts of his boat. He also has full control over the trimming tanks and the storage batteries, both of which I shall tell you about in detail presently.
Right in the line of sight of his eyes is a depth meter by which he can see at a glance at just what depth his craft is moving, and he can also see at what angle[18] the diving rudder, or elevator, as it is called, is set.
A compartment tell-tale (a numbered chart showing each compartment of the boat) also hangs in sight, and if a compartment should begin to leak it is instantly indicated by the tell-tale, which in this case is a miniature electric lamp that lights up back of the number.
By pressing a button he can ring an electric bell in the leaking compartment and so warn the crew that he is about to close the electrically operated bulkhead door and so shut the compartment off from the rest of the boat if the damage done is so serious that it cannot be repaired.
Now the Navigating Compartment.—As you have read before, the conning tower is not a part of the hull but of the superstructure. Now, when the captain or any of his crew wants to get from the conning tower into the hull of the boat he must do so through a hatch in the lower deck which is exactly like the hatch in the top or bridge of the tower.
This arrangement makes it easy to shut off the conning tower into the rest of the boat if it should be seriously damaged by shell-fire or by collision. Should this happen, the boat is steered from another compartment called the navigating room, in which are all of the devices used in the conning tower. So you see there are two complete navigating rooms and an outside deck control by which the submarine can be steered and operated, no matter how badly damaged she may be.
Next, the Diving Control Compartment.—The compartment containing the diving control, by means of which the submarine can be made to dive and to come to the surface, is fitted with the following devices:
First, there is the diving wheel, which works the horizontal or diving rudders.
Next, there is the angle indicator, which is simply a quadrant—that is, a quarter of a circle—marked off into degrees and each degree into quarters. It has a needle which moves over the quadrant as the pilot turns the diving wheel and this indicates the number of degrees up or down the horizontal rudders have moved.
Another instrument is the depth indicator.
Then there is also an indicator which is merely a modified form of a carpenter’s spirit level. This little device shows when the craft is running on an even keel and when it is running with its keel inclined. For instance, should the diving rudder fail to respond to the touch of the man at the wheel, the level would indicate it, as would also the depth indicator.
Other fittings are the levers and the valve controls, by means of which water can be let into the ballast tanks.
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.
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.
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.
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.
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.
So when the order is given, the diving rudders are set at only ½ a degree from the horizontal, as shown in Fig. 28. The craft must move through the water at about 5 knots, which is the proper diving speed. When the conning tower is one-fourth submerged the angle of the rudders is increased to 1¼ degrees.
This angle is held until the conning tower is half submerged; and then the angle is changed to 2 degrees, and it is held there until the conning tower is three-quarters submerged. As soon as this takes place, the angle is decreased to 1¼ degrees again, and the rudders remain at this angle until the dive is completed.
Why a Shallow Dive Is Made.—The reason such a shallow dive must be made is the result of having to let water into the ballast tanks to bring the craft to the awash condition before diving.
If the angle of the dive were to be suddenly increased to 10 or 15 degrees the tilting of the boat would throw all the water forward in the tanks and this would seriously upset her balance, and might even make her settle nose downward to the bottom of the sea.
How the Boat Is Kept Submerged.—When a dive is to be made the diving rudders are set at the angles just mentioned, but water is not let into the ballast tanks at the same time, for this would also tend to destroy the balance of the boat.
But when the captain wants to keep his submarine at a certain depth below the surface of the water after the dive is made he has water admitted to the ballast tanks and this keeps her at that level. When he wants to return to the surface, or “break water,” the water is pumped out and then the diving rudders are set and the boat makes an upward glide.
The Time It Takes for a Dive.—The time needed for a submarine to get ready to dive is about 2 minutes; but this is often long enough for it to become a target if a submarine chaser is on the little war-dog’s trail. Should she be hard pressed she might dive at a steeper angle—say, 5 degrees, but never more, and under ordinary conditions she will never dive at more than 2 degrees’ inclination.
The reason it takes time for a submarine to get ready to dive is because the wireless masts have to be folded in, the machine guns disappeared, and the hatches fastened down. Finally, it must not be forgotten that a submarine can dive only when she is pushing ahead under power. If she is at rest and the captain wants her to sink he must either start her engines or else be content to simply submerge her on an even keel.
The Ballast Pumps and What They Do.—The pumps which pump the water from the ballast tanks are driven by electric motors. They must be powerful pumps, for they not only have to pump the water out of the tanks quickly, but they have to force it out against the pressure of water in which the submarine is submerged; this pressure increases the deeper the boat sinks, and it is often 80 pounds or more to the square inch. The pumps are controlled from the conning tower, and also from the navigating compartment.
What the Buoyancy Tanks Are For.—We said previously that a submarine never loses its buoyancy completely. If she were built like an ordinary ship and simply fitted with ballast tanks, she would sink when these are filled with water and never come up again, for her natural buoyancy would be destroyed. As it is, a submarine has tanks filled with air which keeps her buoyant, and these will bring her to the surface the moment the ballast tanks are empty.
Make this experiment and you will quickly understand how these buoyancy air tanks work: Take an empty bottle and cork it up tight. It looks empty, but as a matter of fact it is filled with air. Push the bottle to the bottom of a bucket of water; let go of it and the instant you do so it will rise to the surface.
A large number of steel air tanks, or buoyancy tanks, or high pressure air-flasks, as they are called, are placed both fore and aft in a submarine, and these are filled with compressed air at a pressure of 2,000 pounds to the square inch. These air-flasks have a tremendous supporting power—which is only another way of saying that they are extremely buoyant.
It must be clear now that even though the submarine is resting on the floor of the ocean it can always rise to the surface by the reserve buoyancy provided by these air-flasks.
Compressed Air and Air-Compressor Pumps.—The air-flasks are filled with compressed air by air-compressor pumps which are driven by the engines when the submarine is running light or awash.
The air compressor is formed of several air pumps coupled together; each air pump is made very much like a water pump, but it sucks the air in from the outside and then forces it into the air-flasks until it is under a pressure of 2,000 pounds to the square inch. To overcome this back pressure, as it is called, the pumps must be extra powerful.
These pumps also supply compressed air for the torpedo tubes, the trimming tanks, and to help blow out the water from the ballast tanks.
Inside the Torpedo Compartment.—The torpedo compartment contains the extra torpedoes in their cradles. Near the tubes from which the torpedoes are shot is the compressed air which furnishes the propulsive power needed to make the torpedoes leave their tubes.
Why Trimming Tanks Are Used.—As a torpedo weighs nearly 1,000 pounds, it is plain that whenever one is shot from the craft it will very greatly disturb the balance of the boat unless some means is used to add weight to it which is exactly equal to the weight of the torpedo.
This is done by what is called the trimming tanks. These are usually placed fore and aft and in or near the torpedo and mine compartments. As soon as a torpedo is shot, or a mine is laid, the trimming tanks are filled with water which makes up for the weight lost and keeps the craft on an even keel.
If, on the other hand, any extra weight is taken aboard the submarine, enough water to equal it is blown out by compressed air.
In the Mine Compartment.—The mine, as the stationary bombs that are to be laid in a harbor or some other strategic point are called, are kept in the mine compartment.
This compartment has a trap door in it through which a mine-layer, that is a man dressed in a diving-suit, can get out of and back into the submarine again, or through which the mines can be lowered.
And Last of All, the Sea Anchor.—A submarine must have an anchor as well as a merchantman. The anchor is of the mushroom type, so called from its appearance; and as you will see from the accompanying picture (Fig. 29), it is very different from the two armed and fluked kind that so resembles an Irishman’s anchor i.e., a pickax.
Where the Crew of a Submarine Lives.—Proper quarters for the officers and crew in the earlier submarines were sadly neglected; but conditions have greatly changed since then—though of course they are not quite so good as living in a luxurious hotel ashore.
Great improvements have been made in behalf of the undersea navigators and sailors, until in the more recent submarines the crew have quarters that compare favorably with those on board a battleship.
There are oxygen tanks that supply pure air, while electric fans set up a forced draft and keep the air cool and make it circulate freely. Then there are electric heaters which keep the temperature just right under all conditions.
It goes without saying that the modern submarine has its galley—that is, its cook room. But, very different from the galley on the old windjammers that used to sail the seas, the sea-cook does not use a cook-stove, which was also called a galley, but electricity.