of stone; it was built on the site of the old smithery. Unlike the earlier timber docks, which were drained using gravity, this new dock (No 3 Dock) was pumped dry using a Boulton & Watt steam engine. After completion of the new dock in 1821, reconstruction of the other docks in stone followed (with the exception of the northernmost, which was converted into a slipway); they were likewise emptied using steam power, provided by the same engine and pumps (which were also linked to a network of pipes installed across the whole dockyard site for firefighting purposes). Another novel application of steam power was embarked on in 1817, with the building of a 'Lead and Paint Mill', in which a single beam engine powered a rolling mill and a series of devices for grinding pigment and mixing paint; the plant was operational from 1819. It was not until 1837, however, that steam power was first introduced into the ropery, and the smithery received its first engine (for blowing the forges and powering tilt hammers) in 1841. At the same time, moves were being made towards the application of steam power to ship propulsion. The first steam-powered ship to be laid down at Chatham was HMS Phoenix, one of four paddle steamers built concurrently across the royal dockyards in the early 1830s, each designed by a different leading shipwright. HMS Bee, launched at Chatham in 1842, was an experimental vessel fitted with both paddles and a propeller, each of which could be driven independently from the same engine for comparison. Following the success of such early trials with screw propulsion, several older sailing ships were taken into dry dock and retro-fitted with propellers, beginning with HMS Horatio. Another hint of changes to come was seen in the launch of HMS Aetna, the first armour-plated vessel to be built at Chatham, in 1856. All these developments were to come together with the construction of HMS Achilles, in a newly expanded No 2 Dock, between 1860 and 1864: the first true iron-hulled battleship to be launched in a royal dockyard. To meet the new demands of building in iron, metal mills were built alongside the smithery in 1845, containing rolling machinery and furnaces for reprocessing iron. Holl's smithery was itself enlarged with the addition of a foundry in the 1850s, and its courtyard was roofed over for a steam hammer shop in