The steam vessels first built for the Navy were hardly worth calling warships and were of little or no value for fighting purposes. The first steam-propelled vessel in the Navy was the _Monkey_, of 210 tons, built at Rotherhithe in 1820 and fitted with engines of 80 nominal horse-power by Boulton and Watt. She had two cylinders of about 35¹⁄₂ inches diameter and 3 feet 6 inches piston-stroke. The _Active_, of 80 nominal horse-power, was launched by the same firm two years later, and in 1823 Messrs. Maudslay began with the _Lightning_ that connection with the Royal Navy which was maintained as long as the firm was in existence. Up to 1840 about seventy steam vessels were added to the Government fleet, the majority of which were given side-lever engines and flue boilers with a steam-pressure of about 4 lb. to the square inch above the air-pressure. All these vessels were chiefly used for towage and general purposes, including mail carriage when necessary, and not as warships. There was a gradual improvement in the size of the vessels, and in 1832 the _Rhadamanthus_ was constructed by Maudslay, Sons, and Field with engines of 220 nominal horse-power and 400 indicated. Her machinery weighed 275 tons. The steamer _Salamander_ appeared in 1832, and thereafter several similarly propelled wooden-hulled steamers were added to the Navy. Between 1840 and 1850 tubular boilers were generally adopted, the boilers being lighter and more compact than those previously in use, enabling the working pressure of the steam to be increased to ten or fifteen pounds above that of the atmosphere. All these vessels had paddle-wheels. Warships similarly propelled were adopted by other nations also, but with the exception of skirmishes with the natives of uncivilised or semi-civilised countries, vessels of this type were not tested in serious warfare until the war in the Crimea. Even then many of the British and French warships were stately wooden three-deckers. Such vessels of the attacking fleets as were paddle-driven usually suffered badly about the wheels when they ventured within range of the Russian guns; while those, chiefly despatch vessels and gunboats, which had screws, were comparatively safe so far as their propellers were concerned, but were too weak to engage the Russian batteries. Floating armoured batteries were therefore decided upon, some of which had screw propellers, single or twin, but from the marine, apart from the military, point of view, they achieved no great success.