Former Detention Centre (Building Number 1/2)

The former detention centre, built between 1882 and 1883, is located at HM Naval Base and is constructed from red brick in English bond with a concealed roof. This long, narrow building has two storeys and consists of nine bays. The first-floor features segmental-arched openings with small-pane metal windows and stone sills. A stepped eaves band sits below a cyma-moulded ashlar cornice, and iron tie-rods are visible at the ends of the building.

On the south-east side, the ground floor is part of the 1704-11 dockyard wall, which includes a segmental-arched entrance leading into the right end of the detention centre. The first floor has pilasters rising beside the two-light bays. The north-west side's ground floor is obscured by the HMS Warrior display tent. The south-west end of the building has three windows on each floor.

Inside, there is a passage along the north-west side with entrances to six cells, which are brick vaulted and feature thick doors with spy-holes. Iron urinals remain on the first floor at the south-west end. This building was part of the security within the late 19th-century yard and served as the formal entrance with the Victory Gate.