stretched in length, and included an area of in excess of . Alongside the four dry docks it now had a total of six shipbuilding slips (equalling Deptford and outnumbering the other yards in this regard), albeit three of the six were under in length and suitable only for building smaller warships. The docks varied from to in length. The officers and men employed in the yard had also increased, and by 1798 they numbered 1,664, including 49 officers and clerks and 624 shipwrights. Additionally required were the blockmakers, caulkers, pitch-heaters, blacksmiths, joiners and carpenters, sail makers, riggers, and ropemakers (274), as well as bricklayers, labourers and others. Building works at Chatham did not compare with the substantial expansions underway at Portsmouth and Plymouth at this time; but the southern part of the yard was significantly redeveloped, with construction of two new storehouses on Anchor Wharf and a major reconfiguration of the ropery. Among the vessels built in this Dockyard which still exist are (launched in 1765 and now preserved at Portsmouth Historic Dockyard) and (a ), launched in 1824 and now preserved afloat at Dundee). Mechanisation Following the appointment of Robert Seppings as Master Shipwright in 1804, iron began to be introduced into the structure of ships being built at Chatham; the following year work began on a new, much larger smithery, commissioned by Samuel Bentham, designed by Edward Holl and fitted out by John Rennie. Among other things, the use of iron in ship construction enabled larger vessels to be built, and between 1836 and 1851 Chatham gained five new covered slipways, much larger in scale than the ones they replaced. (The covering of Chatham's slipways and dry docks, to protect the woodwork of ships as they were built or repaired, had begun with No 2 Slip and No 1 Dock in 1817). In 1811, Marc Brunel recommended the installation of steam-powered sawmills in the royal dockyards, to replace the manual labour of the saw pits. Money was only made available for one such installation, however, and Chatham (as the principal building yard at this time) was chosen as its location. Land was purchased to the northeast for its construction, and the new saw mill began operation in 1814. The following year, John Rennie was engaged to build an entirely new dry dock (following his own recommendations) which was the first in the dockyard to be built entirely