Ministry of Defence Buildings A201 and A202 at Tl 3768800948

MOD Buildings A201 and A202, formerly known as Royal Gunpowder House, are a Mixing House and Saltpetre Mill built between 1787 and 1800. The Mixing House was extended to the north by one bay before 1830 and is linked by a later 19th-century bay to the center. The buildings are constructed of reddish/brown Flemish bond brick, with a hipped roof to the right and ventilators on two pyramidal roofs to the left. They are single-storey structures.

The Saltpetre Mill on the left features gauged brick flat arches over two 20th-century windows and a concrete lintel above a late 18th-century heavy plank door on the right. The mid-19th-century entrance bay in the center has a red brick flat arch over a half-glazed mid-20th-century door. The Mixing House has a timber lintel over an early to mid-19th-century four-panelled door, flanked by segmental arches over 20th-century two-light windows. An early 19th-century extension to the right has a similar window and a timber lintel over a late 19th-century four-panel door with an overlight set in a beaded wood architrave. The buildings have stepped brick eaves.

Inside the Mixing House, there is a 3-bay king-post roof with soffit bolts, raking struts, and diagonal corner bracing to the wall plates; other roofs are not visible. The Mixing House was used for mixing saltpetre and sulphur with charcoal, which were then crushed in the incorporating mill. A set of drawings from 1830 provides detailed records of these buildings and the utensils used within them. This site is an important and unique survival associated with the late 18th-century gunpowder industry and groups with the contemporary Walton House, A200.