Signal (Flagstaff) Hill Battery was established in 1879 three 68-pdr SB 4.7 tons guns were mounted on Flagstaff Hill to protect the harbour and can still be seen although not in their original position. A decade later it was decided that these 68-pdr guns were inadequate and a plan were drawn up to mount an Armstrong 6-inch Mark V gun on a hydro pneumatic disappearing mount. The battery was built between 1890 and 1891 and was commissioned in 1892. The battery had underground magazines and access which has all be backfilled.
The New South Wales Government Heritage- The Environment, Energy and Science (EES) Group summarise the surviving positions as:
The fortification that can be seen today is the deep 1890 circular concrete pit – excavated into the hillside, that contained an Armstrong and Co Mark V 6-inch breech loading hydro pneumatic disappearing gun mounted in the pit. In the gun pit can be seen doorways to the tunnels that lead back into the hill to the underground cartridge and shell stores and the casemate. The gun emplacement was flanked by a depression range finder position and an observation station connected by underground passages to the Fort. There were also two machine gun posts on the southern side of the Fort. The entrance to the underground stores is through a brick wall, that has one doorway and two window openings, set into the hillside on the southern side of the emplacement. It can be seen from the car park that originally was the battery yard. The filled in gun pit was dug out in 1999-2000. No remains of the guns survive other than the embedded metal circular track on the floor of the gun pit on which the gun carriage rotated.
This battery was intended to operate in conjunction with the two guns at Smith’s Hill Fort.