The Admiralty relented towards iron for shipbuilding in 1840, when it had the paddle-steamer _Dover_ built at Birkenhead, and three small iron gunboats followed from the same establishment before the end of the year. The demonstration afforded by the _Garry Owen_ has been alluded to. The _Great Britain_, that magnificent pioneer of the iron screw steamship, launched at Bristol, in December, 1844, ran on the rocks at Dundrum Bay on the coast of Ireland, in 1846, and was successfully refloated after being ashore for nearly eleven months, during which she withstood several severe gales. After this it was no longer possible either to ignore the superiority of iron over wood for constructional purposes, or to doubt the immense strength with which an iron ship could be built. The enterprise and daring of Brunel in designing this ship without any data to go upon stamp this vessel as an evidence of his extraordinary genius. She was in a sense the forerunner of the _Great Eastern_, for she demonstrated what could be done with iron; and the _Great Eastern_, constructed on the longitudinal system, though a commercial failure, proved the advantages of that system for vessels of such remarkable length, as to a large extent her design solved the problem of overcoming the sagging and hogging strains and showed the Admiralty what could be achieved in contending with this difficulty. This success helped in no slight degree to the introduction of the iron-clad citadel system some years later. The success of the _Archimedes_ and the _Great Britain_ demonstrated the power of the screw, and in the latter that iron must be the material for future ship construction, whether in the navy or the mercantile marine. The Government clung to wood for all its fighting ships as long as it could, but it decided to try the screw propeller, without, however, abandoning the paddle-wheel, and many fine vessels were launched.