New Bastion, including part of the counterscarp wall

New Bastion, built in the 1850s and 1860s, is a military bastion that includes the main bastion wall and part of the counterscarp wall. The listing does not include the mid-20th century stone steps leading from the top of the bastion down the east wall to the ditch below, the mid-20th century metal vehicular entrance gates in the counterscarp, or the 20th century brick buildings within the bastion ditch. The southern part of the counterscarp wall, which is truncated and partially rebuilt, is also excluded from the listing.

The bastion features a Plymouth-limestone ashlar scarp wall with a rubble-limestone counterscarp wall. It has an angular plan, facing east and south, with a parallel counterscarp wall. The ashlar-faced scarp wall is topped by a rolled cordon and is abutted and overlain to the north-west by the rubble-stone wall of the new lines. The southern side of the rampart includes musket loops that overlook the approaches to the Old Gun Wharf. The rampart is topped by an earth bank, which is partially lined on the interior by a low stone rampart.

A rectangular expense magazine projects from the centre of the eastern bastion wall to the south-west. It features a brick-arched entrance on the north side, leading into a brick-vaulted chamber. The bastion has been incorporated into the gardens of Admiralty House, resulting in minor adaptations to the internal bastion wall. The exterior of the bastion retains part of the counterscarp wall, which is constructed of rubble stone and survives around the south-east corner. Its western flank has been truncated and largely rebuilt due to the construction of the mid-20th century Maritime Headquarters Bunker.