Just as a navy requires floating distilleries, floating coal stores and floating docks, so does it find very important uses for a floating workshop, which can accompany a fleet to sea and execute such repairs as might otherwise entail the return of a ship to port.

The British Navy has a valuable ally of this kind in the torpedo depÔt ship Vulcan, which contains so much machinery, in addition to the "auxiliaries" already described, that a short account of this vessel will be interesting.

The Vulcan, known as "The Nurse of the Navy," was launched in 1889. She measures 350 feet in length, 58 feet in beam, and has a displacement of 6,830 tons. Her bunkers, of which there are twenty-one, hold 1,000 tons of coal, independently of an extra 300 tons which can be stowed in other neighbouring compartments. When fully coaled she can cruise for 7,000 miles at a speed of 10 knots; or travel at first-class cruiser speed for shorter distances.

The most striking objects on the Vulcan are two huge hydraulic cranes, placed almost amidships abreast of one another. They have a total height of 65 feet, and "overhang" 35 feet, so as to be able to lift boats when the torpedo-nets are out and the sides of the vessel cannot be approached. The feet of the cranes sink 30 feet through the ship to secure rigidity, and the upper deck, which bears most of the strain, is strongly reinforced. Inside the pillar of each crane is the lifting machinery, an hydraulic ram 17 1 / 2 inches in diameter and of 10-foot stroke. By means of fourfold pulleys the lift is increased to 40 feet. When working under the full pressure of 1,000 lbs. to the square inch, the cranes have a hoisting power of twenty tons. In addition to the main ram there is a much smaller one, the function of which is to keep the "slings" (or cables by which the boat is hoisted) taut after a boat has been hooked until the actual moment of lifting comes. But for this arrangement there would be a danger of the slings slackening as the boat rises and falls in a seaway. The small ram controls the larger, and the latter cannot come into action until its auxiliary has tightened up the slings, so that no dangerous jerk can occur when the hoisting begins.

The cranes are revolved by two sets of hydraulic rams, which operate chains passing round drums at the feet of the cranes, and turn them through three-quarters of a circle.

On the Vulcan's deck lie six torpedo boats and three despatch boats. The former are 60 feet long, and can attain a speed of 16 knots an hour. When an enemy is sighted these would be sent off to worry the hostile vessels with their deadly torpedoes, and on their return would be quickly picked up and restored to their berths, ready for further use.

The cranes also serve to lift on board heavy pieces of machinery from other vessels for repair.

Down below decks is the workshop, wherein "jobs" are done on the high seas. It has quite a respectable equipment: five lathes, ranging from 15 feet to 3 1 / 2 feet in length; drilling, planing, slotting, shaping, punching machines; a carpenter's bench; fitters' benches; and a furnace for melting steel. There is also a blacksmith's shop with an hydraulic forging press and a forge blown by machinery; not to mention a large array of tools of all kinds. Special engines are installed to operate the repairs department.

The Vulcan also carries search-lights of 25,000 candle-power; bilge pumps which will deliver over 5,000 tons of water per hour; two sets of engines for supplying the hydraulic machinery; air-compressing engines to feed the Whitehead torpedoes; a distilling plant; and last, but by no means least, main engines of 12,000 h.p. drawing steam from four huge cylindrical boilers 17 feet long and 14 feet in diameter.

Altogether, the Vulcan is a very complete floating workshop, sufficiently speedy to keep up with a fleet, and even to do scouting work. Her guns and her torpedo craft would render her a very troublesome customer in a fight, though, being practically unarmoured, she would keep as clear of the conflict as possible, acting on the offensive through the proxy of her "hornets." She constitutes the first of a type of vessel which has been suggested by experts, viz. one of high speed and unarmoured, but capable of carrying a swarm of torpedo boats which could be launched in pursuit of the foe. Even if 50 per cent. of the craft were destroyed, the price would be small if a single torpedo were successfully fired at a battleship. The naval motor boat, to which reference has already been made, would just "fill the bill" for such a cruiser; and in the event of a score of them being dropped into the water at a critical moment, they might easily turn the scale in favour of their side.