Of the 689 vessels of all kinds constituting the British navy in 1897, there are only about twenty-two wooden ones, and these are nearly all used either as store ships or training ships, seldom, if ever, to leave their anchorage. And so entirely has the paddle-wheel been superseded by the screw-propeller, there are not left a dozen paddle-steamers in the entire fleet, including the Queen’s yachts and a few light-draught river boats. As already mentioned the compound engine was introduced into the navy in 1863. The twin screw was first applied to the _Penelope_ in 1868, and has since become universal in vessels of war, the result of these improvements being a marvellous increase of power and speed, with a great saving of fuel. Roughly speaking, a pound of coal is to-day made to produce four or five times the amount of power that it did in 1837. Experiments had been made with steam power in the navy as early as 1841. In 1845 as many as nineteen sets of screw engines had been ordered for the Admiralty, but it was not until some years later that it came into general use. About 1851 the _Duke of Wellington_,[30] the _Duke of Marlborough_, the _Prince of Wales_, etc., all full-rigged ships, each armed with 131 “great guns,” were fitted with auxiliary steam-engines of from 450 to 2,500 horse-power. The introduction of iron armour-plating—first practised by the French towards the close of the Crimean war—presaged the beginning of the end of “the wooden walls of Old England,” and the disappearance forever of the beautiful white wings that had spread themselves out over every sea. [Illustration: TORPEDO DESTROYER “HORNET,” 1896.]