The submarine boat, as well as most of the other boats of a like character that have been experimented with for nearly 300 years, should more properly be called a diving-boat. Its purpose is to duck under water and remain there as long as may be necessary when its own safety is in danger. When it engages in a fight, it will begin its work by a series of dives before discharging one of its five torpedoes from the bow. Much as a stone may be made to go skipping across the top of the water, so this boat may be made to skip along underneath the water, coming occasionally to the top. Although it will remain underneath the water only six hours without coming up when it is being worked at its full capacity, it will be able to remain under the water for several days if it is simply necessary to keep out of sight for a long time. As fast as fresh air is needed a float with a hose attached is released, and when it reaches the surface of the water the electric motors suck down enough air in a few minutes to fill the tanks again, and the stay may be prolonged until the supply of water and provisions gives out.
The boat is known as the Holland submarine boat, because it is the invention of Mr. John P. Holland, who has been studying this problem for more than twenty years. In his experiments he has gone under water, for a stay of from a few minutes to several hours, more than fifty times. In spite of discouragements that would have made many a man give up, Mr. Holland kept on, until he convinced the government that his boat was not only feasible, but an absolutely necessary article in the equipment of an up-to-date navy. Other countries have submarine boats, but none of the boats has been fully successful; and if this vessel will really accomplish what it is expected to do, the United States will again show the world that it excels in naval ship-building.
The use of electricity in propelling boats and the power to compress air in tanks makes navigation under water a comparatively simple matter. Remaining under water is the easiest part of the task required of a submarine torpedo-boat. The essential things are that the boat must be speedy in diving and in coming to the surface, that some means of steering accurately must be devised, that the boat must be kept at a certain level in the water, that it must have good speed under the water, and that it must be able to discharge torpedoes safely under vessels which it is attacking. If the vessel is successful it will solve the problem of harbor defence, for no fleet would dare venture into a harbor knowing that one of these submarine boats was on guard.
TAKING AN OBSERVATION OF THE ENEMY'S FLEET.
Every boat, no matter what its object, must have a certain amount of buoyancy to make it float. This vessel has the usual amount for one of its size. In its hold are a certain number of air-tanks, in which are stored 30 cubic feet of compressed air at a pressure of 2000 pounds to the square inch. There are also 620 electric storage batteries for propelling the ship when the steam is shut off under water. Let us take the little vessel under water. We have been running along under steam on the surface and have seen the enemy. All the hatches are closed water-tight, and the Captain goes into a little armored turret. He gives the word to run awash. At once the valves in the bottom of the boat are opened, and certain apartments are allowed to fill with water. This sinks the boat at once so that only the turret is visible. The enemy is near and has seen us. It is necessary to dive. Quickly the word is given, and the smoke-stack is dropped down into the ship and a thick plate is clamped over it. The fires are banked, and the engine is disconnected from the screw, and the electric power is attached. An indicator tells the depth we have reached, and then the mechanism is set at the required depth, and we are soon skimming along under the water in absolute safety. The air in the tanks is being released as fast as we need a fresh supply, and we are dry and comfortable.
DAVID STRIKING GOLIATH.
The Captain decides that he wants to look around. He steers the boat up to within four feet of the surface, and then he pokes up out of the water what looks like a stove-pipe. Its real name is a "camera lucida." It is an arrangement whereby those inside the turret can get a good look around by means of mirrors. The Captain decides to go under again, and makes for his target. He is soon passing under a ship. The darkened water tells us so. He makes a short turn, or stops, and then backs away and gives a signal to discharge a torpedo. It leaves the boat with a rush, and in a few seconds there is a muffled roar. A great war-ship has been struck. It lurches and staggers. Pandemonium reigns on it, the order is given for every man to save himself, and in less than five minutes after the torpedo has been discharged a five-million-dollar battle-ship, the most powerful engine of destruction man ever made, is lying at the bottom of the channel, and the enemy has received a mortal blow. We come up to look around again. David has struck Goliath with a stone in the forehead and killed him.
How is the diving done? If you will look at the boat you will see at the stern two horizontal rudders. They stick out behind like the feet of a swan as it swims about a lake. When it is necessary to dive, these flat rudders are tipped down in the rear, and the ship is forced under at the bow at an inclination. When the required depth is reached the rudders are flattened out, so to speak, or held at the inclination to keep the vessel on an even keel, the tanks having been filled to overcome all but a very small reserve buoyancy. An automatic arrangement allows the water to press on a rubber diaphragm, and keeps the boat at an even depth. It is a great problem, however, to steer absolutely straight. It has been found that under water the mariner's compass is not trustworthy. Mr. Holland devised an ingenious arrangement to overcome this. There is a triangular drag floating just above the diving-rudders. It is necessary, when the boat is running on the surface, to put it on the exact course it is to follow just before the dive is made. The rudders are tipped, and then this drag comes into play. If the boat veers to the right or left this drag sways to the opposite side. It is so arranged that it works a lever that at once swings the steering-rudder of the ship to the side that will bring the boat straight on its course again.