This wheel turns on a vertical shaft, and its paddles are feathered by an eccentric cam in such a manner that at one part of their revolution they have a pushing and drawing action on the water, while at another part they present only their edges. In fact it is simply a feathering paddle wheel, turned horizontally instead of vertically. By suitably turning the cam wheel, which is done from the helm, the feathering of the paddles is caused to occur at different points; and in this way the vessel may be turned, or rather her stern twisted around, as if on a pivot. At the same time, by suitably adjusting the paddles, the ship goes ahead, or astern, the engine meanwhile running in the same direction. By the apparatus above described it is considered that the _Alarm_ is afforded not only a means of speed, but of being handled with the utmost readiness, which latter is absolutely essential in such a vessel, as she must always meet her antagonist bows on. 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. [Illustration: THE "ALARM" TORPEDO SHIP. PLATE XLV]