But when men like Brunel, Scott Russell, and Laird of Birkenhead, were loudly advocating the adoption of steam-propelled war vessels, and the steamers were proving their superiority over the sailing ships in every respect, the Admiralty was compelled to pay attention. These men also urged the adoption of iron in place of wood for shipbuilding. The idea was ridiculed. It was in vain that it was pointed out that, though a piece of iron would sink and a piece of wood of the same size would float, the true test of buoyancy lay in the total weight of the material used in the construction of a hull, and that a hull of given external dimensions and built of iron would be more buoyant than a hull of the same dimensions and built of wood, and that the difference in favour of iron amounted to as much as 20 to 35 per cent. The mere fact that iron steamers were already in existence had little influence with the Admiralty. The first of these was the _Aaron Manby_, built at Horsely in 1821, for Captain (afterwards Sir) Charles Napier and the gentleman after whom she was named. Others were doing service in Ireland. In 1832, Messrs. McGregor, Laird and Co. had the _Elburkah_ constructed for employment on the Niger; she was 70 feet long, by 18 feet beam, and 6 feet 6 inches depth. Two years later Mr. Laird built at Birkenhead the _Garry Owen_, a little vessel only 125 feet long and fitted with two engines of a total of 90 nominal h.p. She went ashore during a gale on her maiden voyage, having as companions in misfortune several wooden vessels, and was the only one to be refloated, being little the worse for her misadventure. This proved the strength of an iron-built ship beyond doubt, and iron coasting steamers after this became comparatively numerous. The first iron warship, a frigate, was proposed by Laird in 1836, and built at his yard at Birkenhead in 1842; it was offered during construction to the Admiralty, which would have none of it, so it was sold to the Mexican Government, which christened it the _Guadeloupe_. This vessel was 175 feet in length, by 30 feet 1 inch beam, and had a depth of hold of 16 feet. The East India Company appreciated the value of iron steamers suitable for war purposes, and placed an order with Laird in 1839. One of those, the _Nemesis_, built under this order, went to India via the Cape, and took part in the China operations in 1840-2. She was struck several times by cannon balls and holed. Her commander, Captain Hull, reported in his evidence before the Royal Commission, in 1848, on the naval estimates, that the holes were made clean and without splinters, thus disposing of the theory that iron when struck by a shot would splinter worse than wood. Her armament consisted of two 32-pounder pivot guns so mounted as to give her a wide range of fire, and as she drew but five feet of water she may be regarded as the first of the shallow river-gunboats which have done such excellent service in so many parts of the world.