From the Register of Scheduled Monuments: Circular armoured turret containing pair of 80 ton RML Armstrong guns, built on the 'Frazer' system. Constructed in 1873. Originally steam driven. Machinery space below turret remains but steam engine and boilers are missing. Apart from the turret itself, the rest of the installation is massively constructed of stone, brick and concrete. These are the second largest armstrong guns ever made and the last in the UK still on their original carriages and in their original setting.