direction in which they are aimed, from power and mechanism contained within themselves. They are wonderful pieces of mechanism and cost several thousand dollars each. They are virtually miniature submarine boats. The essential features of the automobile torpedo are the airflask, the warhead, the depth control, and steering and propelling machinery. The airflask forms the central section, which is a steel tank containing compressed air stored at high pressure; about twenty-five hundred pounds per square inch is the present practice. When the torpedo is expelled from the torpedo tube this air is automatically turned on to run the engines. It passes through reducing valves and heaters to drive either a multiple cylinder or a turbine engine, and revolves two propellers, running one clockwise and the other counterclockwise, set in tandem at the stern of the torpedo. The propellers, running in opposite directions, thus enable the torpedo to be more easily steered by the delicate automatic steering machinery. A diaphragm operated by the pressure of the water operates control mechanism which regulates the depth. An instrument called the "Obry gear" steers it in the horizontal plane. The essential feature of the "Obry gear" is a gyroscope which is started when the torpedo is ejected from the tube. It is instantly speeded up either by a powerful spring or an air turbine to about fifteen thousand revolutions per minute. The peculiarity of the gyroscope is that it has a tendency to hold the direction in which it is started. Hence, if the torpedo starts swerving either to the right or left from the direction in which it is aimed, the gyroscope causes certain valves to function which will automatically set the steering rudder to bring the torpedo back into its original course. The "Gyro" will continue this control until the torpedo has completed its course, which in some of the latest types is said to be about five miles.

The warhead is the forward portion of the torpedo and contains usually wet gun-cotton, which is a safe high explosive and can be exploded only by a detonating charge of the more sensitive explosives. This detonating charge is placed in a tube screwed into the forward end of the torpedo. Extending out from the forward end of the tube is a small propeller, the purpose of which is to set the firing mechanism after the torpedo has run a certain distance from the vessel from which it has been fired. This is a safety device to prevent the torpedo from being exploded near its own ship. The torpedo running through the water causes the propeller to revolve, which turns a shaft. After the shaft makes a certain number of revolutions it sets a firing pin, and then if it hits an object it will explode. Many modern torpedoes are loaded with trinitrotoluol. This is a much more powerful explosive. According to experts, the explosion of two hundred and fifty pounds of T-N-T, as it is called, will destroy any battleship ever built.

RAPID-FIRING GUNS

Courtesy of the Scientific American

Rapid-fire disappearing guns may be quickly elevated above armored turret when the submarine rises to the surface.

Divers' Compartment.—Some submarines are fitted with a divers' compartment, from which compartment mines may be planted, either when on the surface or when submerged. This compartment is fitted with a door which opens outwardly in the bottom of the boat. It is shut off from the living and machinery rooms of the vessel by an air lock and heavy pressure-resisting doors. The divers' door may be opened when the vessel is submerged and navigating on the bottom, and no water will come into the vessel when the door is opened. This is accomplished in the following manner: The members of the crew who wish to go outside the vessel first go into the diving compartment. They close the door which shuts them off from other parts of the vessel. They then turn compressed air gradually into the compartment until the air pressure in the compartment equals the water pressure outside. If the depth is one hundred feet the air pressure in the compartment would need to be 43.4 pounds per square inch; if the depth is two hundred feet, twice that, or 86.8 pounds per square inch, etc. When the air pressure in the compartment equals the water pressure outside, at any depth, the door in the bottom may be opened and the water will not rise up into the compartment, because the air pressure keeps it out. Tests have been made which show that it is safe for divers to go out from compartments of this kind in depths up to two hundred and seventy-five feet.

DIVING COMPARTMENT

This view shows the diving compartment being used for the purpose of grappling for the electric cables controlling fields of submarine mines. Operating in this manner, the diving compartment becomes a veritable travelling diving-bell, and when the air pressure in the diving chamber is made to balance with the water pressure outside the diving door may be opened and yet the water will not enter the working chamber.

Dangers.—Years of painstaking development work have eliminated most of the dangers connected with the operation of submarines in times of peace. The experienced designers have learned the importance of having great submerged stability, so that no modern craft is likely to make an unexpected headfirst dive into the mud, hard sand, or rocks on the bottom. This was a common occurrence not many years ago. Another danger to be avoided is that of asphyxiation by the escape of noxious gases from the engines. The blowing up of the vessel by the ignition of hydrogen fumes from the battery is another risk to be guarded against. In the latest vessels the noxious gases from the engine are not permitted to escape into the engine-room; gasolene is rapidly giving place to heavy-oil engines which do not use an explosive fuel, and the hydrogen gas given off during the charging of batteries is pumped overboard as rapidly as it is generated. Consequently modern submarines, when navigating on the surface, are as safe as any surface ship. In fact, they are safer, from the fact that they are so much more strongly built and that they are divided into compartments. Any one of these compartments could be filled by water in an accident and the remaining compartments would keep the ship afloat. In submerged peace-time navigation the dangers are those of collisions with surface vessels, uncharted rocks, or sunken ships. The danger of collisions with surface ships may be avoided by keeping below the depth of keel of the deepest draft surface ship, when long under-water runs are being made, and always stopping machinery to listen for the sound of surface ships before rising to the surface. If running near the surface where periscopic vision is possible, constant vigilance must be maintained, as there are no rules of the road or right of way which may be claimed by the submarine commander, owing to the fact that the lookout on the surface craft, in all probability, cannot see his little periscope in time to avoid collision.

A MODERN SUBMARINE CRUISER, OR FLEET SUBMARINE (LAKE TYPE)

The parts indicated by numbers in this illustration are as follows: 1, main ballast tanks; 2, fuel tanks; 3, keel; 4, safety drop keel; 5, habitable superstructure; 6, escape and safety chambers; 7, disappearing anti-aircraft guns; 8, rapid-fire gun; 9, torpedo tubes; 10 torpedoes; 11, twin deck torpedo tubes; 12, torpedo firing tank; 13, anchor; 14, periscopes; 15, wireless; 16, crew's quarters; 17, officers' quarters; 18, warhead stowage; 19, torpedo hatch; 20, diving chamber; 21, electric storage battery; 22, galley; 23, steering gear; 24, binnacle; 25, searchlight; 26, conning tower; 27, diving station; 28, control tank; 29, compressed-air flasks; 30, forward engine room and engines; 31, after engine room and engines; 32, central control compartment; 33, torpedo room; 34, electric motor room; 35, switchboard; 36, ballast pump; 37, auxiliary machinery room; 38, hydroplane; 39, vertical rudders; 40, signal masts.

How the Submarine Works.—Reference to the diagrammatic view of a modern submarine will probably make clear the following explanation of the operation of a submarine. We will assume that our submarine leaves her own harbor with fuel, stores, and torpedoes on board, wireless and signal masts erected. She is bound to a station farther down the coast, but receives word by wireless that an enemy fleet has been seen approaching the coast in such a direction as to indicate an attack on New York. She receives instructions to return and take up a station fifteen miles off Sandy Hook, the entrance to New York Harbor, and also that she is to coöperate with the smaller harbor-defense submarines that are permanently located in New York. She therefore puts back to the station designated. All deck fittings and lines are stowed except the ventilators and the deck wireless outfit; the latter is left standing so as to keep in touch with the scout ships and destroyers which are reporting the approach of the enemy. Shortly after arriving at her station, the commander notes smoke on the horizon and orders are given to "prepare to submerge." Each member of the crew then proceeds to his particular task; the wireless masts and ventilators are quickly housed, and all hatches are closed and secured. The quartermaster and submerged-control man who controls the steering and hydroplane operating gear take their stations in the control department. The engines are uncoupled by means of the rapid operating clutch, the electric motor is coupled, the hydroplanes are unfolded, the valves are opened, and the word is passed to the commander, "All ready for submergence!" All this is done in a modern vessel in less than two minutes.

The command is then given: "Fill main ballast!" Quick-opening valves are opened and the water rushes into the ballast tanks and superstructure at the rate of fifty or sixty tons per minute. The order is then given: "Trim for submergence!" Sufficient water is then admitted into the final adjustment and trim tank to give the desired buoyancy and trim, and the vessel is now ready to submerge on signal from the commander, who now takes his station at the periscope. The gunners have also taken their stations at the torpedo tubes to prepare to load the tubes as soon as the torpedoes already in the tubes are discharged. The whole time consumed from the time word to "prepare to submerge" until the vessel is running under water has probably not been over two or three minutes. In the meantime the enemy has been rapidly approaching and her superstructure is already above the horizon. The commander of the submarine notes that if the enemy holds its course it will be advantageous to change his position to intercept the oncoming fleet. He therefore gives word to submerge to the desired depth and gives the quartermaster the course, and the vessel proceeds, entirely submerged, to get nearer the enemy's line of approach. The commander then brings his submarine to rest before extending his periscope above the surface. As soon as the enemy is found to be coming within range he manœuvres his ship so that his torpedoes will bear the proper distance in advance of the ship he selects to destroy. To make a hit it is necessary to fire in advance of the oncoming ship to allow for the time the torpedo takes to reach the point where the enemy will be. Range finders, torpedo directors, and rapid calculators enable the commander to calculate this to a nicety. If the distance is only a thousand or fifteen hundred yards, a hit is pretty certain to be made, but the greater the distance the less the chance of success and the greater the opportunity for error.