Through all the subsequent changes of armament up to the Crimean War, from solid shot to shell-fire, the truck carriage maintained its place of favour. In 1811 Colonel (afterwards Sir William) Congreve had published a treatise demonstrating the defects of the truck carriage and proposing in its place a far more scientific and ingenious form of mounting. It lacked, however, some of the characteristics which, as we have seen, gave value to the old truck carriage. Except where special conditions gave additional value to its rival, the truck carriage kept its place. In 1820 an iron carriage was tried officially, for 24-pounders, but gave unsatisfactory results. In 1829 the Marshall carriage was tried, offering important advantages over the standard pattern. Its main feature was a narrow fore-carriage separate from the recoiling rear portion, this fore-carriage being pivoted to a socket in the centre of the gun-port. But still the truck carriage survived the very favourable reports given on its latest rival. As concentration of fire became developed new fittings such as directing bars, breast chocks and training racers made their appearance and were embodied in its design. As the power of guns and the energy requiring to be absorbed on recoil increased, the rear trucks disappeared and gave place, in the two-truck Marsilly carriage, to flat chocks which by the friction of their broad surfaces against the deck helped more than trucks to deaden the motion of the carriage. The quoin, perfected by the addition of a graduated scale marked to show the elevation corresponding to each of its positions, gave place at length to various mechanical forms of elevating gear. The elm body was replaced by iron plates bolted and riveted together. And then at length, with the continuous growth of gun-energy, the forces of recoil became so great that the ordinary carriage constrained by rope breechings could no longer cope with them. The friction of wood rear-chocks against the deck was replaced by the friction of vertical iron plates, attached to the carriage, against similar plates attached to a slide interposed between carriage and deck, and automatically compressed: the invention, it is said, of Admiral Sir Thomas Hardy. The truck carriage, as it had been known for centuries, had at last been left behind in the evolution of naval artillery. * * * * *