Gunboat Yard boundary walls, watchtowers and gates

Gunboat Yard boundary walls, watchtowers, and gates were built in 1856. The design was by the Admiralty Works Department, under Colonel Greene, the Director of Works, and William Scamp, the Deputy Director of Engineering and Architectural Works. Construction of the brickwork was entrusted to Messrs Rigby of London.

The red brick walls, laid in Flemish bond, enclose the gunboat yard on the south-east and north-east sides, with a surviving section now forming part of the south-west elevation of No 1 Ship Tank, constructed in 1886 and extended in 1957 for the Admiralty Experiment Works. Three watchtowers are present: one at the junction of the walls, and further towers at the north and south extremities. The main gates are centrally located on the north-east wall; two inserted gateways are on the south-east wall, with a break in the walls allowing access to the engine house complex. The walls extend to form an entranceway to the former burial ground at the southern corner.

The walls are approximately 4 meters high and feature regularly recessed panels along their length. Ramps, in the form of curved steps to the coping, adjust the wall height to accommodate changes in the topography. A projecting brick course is topped with a canted brick coping.

The main gates are flanked by substantial pedimented sentry posts, hollow within and containing slit windows for guards. A round-arched opening is blocked on the north-west side, with recessed arches inside for sentries. Two secondary gates are blocked on the south-east elevation, featuring narrower piers with stone bands and overhanging stone pier caps; a 20th century entrance is set back from the wall line and has square piers with pyramidal stone caps. The burial ground entrance is built in a matching style, with curved walls and a blocked central opening.

The two-storey watchtowers are square, with outward-facing round-arched slit windows on each storey. They have a brick corbel table and pyramidal roofs. The inner walls of the towers include segmental arched openings to the ground floors, with flights of steps built along the walls leading to short sentry walks on the upper floor, creating arched shelters below.