The steering is accomplished from the wheel house located aft on the deck, or below deck, as all the appliances in the wheel house for steering, &c., are duplicated below. By means of a hand lever beneath the wheel, steam is admitted to a small auxiliary engine which works the cam that adjusts the paddles. Then by turning the horizontal hand wheel in either direction, the helmsman controls the movement of the cam, as desired. Just above the wheel is a dial with a pointer, which enables him to note the position of the paddles, and so adjust them as ordered. Inside the wheel house there are also devices for communicating with the men working the bow gun, and with those managing the torpedoes.
Her Armament—Engines.—At [Fig. 146] is shown the spar and mode of working it. It consists of a long hollow iron cylinder lying on its supports between decks. Its outboard end rests in a kind of trough, and to this extremity the torpedo is fixed. The spar is controlled by means of tackles and a steam winch. The side spars are 18 feet, and the bow spar 32 feet in length. If the hostile vessel is defended by torpedo guards, by means of a mechanical contrivance the torpedo signals the fact, and is not exploded until the vessel has forced the obstructions. The engines of the Alarm are compound, with four cylinders, the condenser being placed between them. There are four cylindrical tubular boilers with an aggregate heating surface of 4,600 square feet. Her speed is about 16 knots. Her upper deck is only 3 feet above the water. She is fitted with an electric light, and also with machine guns on her broadside.[N]
This is undoubtedly a most formidable vessel, both as a ram and a torpedo ship, and if capable of performing all that is expected of her, will prove a valuable addition to the United States Navy.
THE "ALARM" TORPEDO SHIP.
Captain Ericsson's Torpedo Vessel "Destroyer."—This torpedo vessel was devised and built by Captain John Ericsson. The Destroyer is 130 feet long, 11 feet deep, and 12 feet beam, extreme; both ends of her hull are precisely alike, and terminate with very fine wedges. The rudder is attached to a vertical wrought iron post welded to a prolongation of the keel, just abaft the propeller, as shown at [Fig. 147]. The tillers consist of thin plates of iron riveted on opposite sides of the rudder, a few inches from its bottom. These tillers are operated by straight rods connected to the pistons of horizontal hydraulic cylinders of 5 inches diameter, which are attached to the sides of the keel. The steering gear by the above arrangement is placed 10 feet below the water line, while the top of the rudder is 6 feet below the same, and thus perfect security is afforded to this most important feature of a torpedo vessel. The intention of the designer in constructing this vessel is to render her so far impregnable, that in attacking bow on she can defy the opponent's fire, at the same time offering absolute protection to her commander and steersman, and also protecting the base of her funnel. The leading feature of the construction of the hull of the Destroyer is its being provided with an intermediate curved deck, which extends from stem to stern, and which is composed of plate iron strongly ribbed, and perfectly water-tight. This intermediate deck supports a heavy solid armour plate, fixed transversely to the line of keel, and 32 feet from the bow, inclined at an angle of 45°, and supported on its after side by a wood backing 4 feet 6 inches in thickness. Behind this formidable shield the steering wheel is manipulated, a wire rope extending from its barrel to a four-way cock placed near the stern, by means of which water pressure is admitted alternately to the hydraulic cylinders, previously mentioned, the motion of whose pistons actuate the rudder. The lower division of the vessel is ventilated by powerful blowers, and contains the machinery; it also affords a safe retreat for the crew during the attack. The upper division is filled with blocks of cork, excepting a small part near the bow, occupied by the aforesaid armour plate and wood backing.
The deck house is 70 feet long, and composed of plate iron, riveted water-tight to the upper part of the hull. As there are no openings in the sides of this deck house, the vessel may be run with her upper deck under water.
Armament of the "Destroyer."—The Destroyer is to be armed with torpedoes somewhat similar to the projectile torpedo, drawings of which were submitted by Captain Ericsson, the inventor, to Emperor Napoleon III. in 1854. The present weapon is composed of a solid block of light wood, the explosive charge being contained in a metallic vessel inserted at its forward end. Instead of being circular, as was the case with the original torpedo, its transverse section is square, with parallel top and bottom and vertical sides, forming very sharp wedges at both ends, cased with steel plates. The extreme length of the Destroyer torpedo is 23 feet. Ignition is effected by means of a percussion fuze placed in the head of the weapon.
Operating the Torpedo.—The method of operating the torpedo is that of inserting it into a horizontal tube near the bottom of the vessel, provided with valves for keeping out the sea during the process of insertion, as shown at [Fig. 148]. When near the hostile vessel, this valve is opened, and the torpedo expelled by a piston actuated by steam power, the expulsion being effected without recourse to gunpowder or other explosive agent. The area of the actuating piston of the Destroyer is 314 square inches, while the sectional area of the projectile is only 196 square inches; this difference in size of the two areas is a special and important feature of the invention, as will be understood from the following: the tension of the acting medium in the Destroyer exceeds 200 lbs. per square inch, therefore the torpedo will be pushed out by a force of (314 × 200) / 196 = 320 lbs. per square inch, and as the distance passed by the piston while impelling the torpedo is 30 feet, an energy of nearly 2,000,000 foot-pounds will be imparted to the projectile.