This Battery was named after Lieutenant General Charles O'Hara, Governor of Gibraltar 1787 - 1799. He believed that if only the Rock could be a little higher, his lookouts would be able to see the Spanish ships as they left Cadiz. For this reason he had a tower built on top of the highest point of the Rock where O'Hara's Battery stands today. It proved to be a failure and was later known as "O'Hara's Folly". It was demolished in 1888 and in 1890 a 6 inch BL gun on a Vavasseur centre pivot mounting was installed only to be replaced in 1901 by the current 9.2 inch gun.
The gun was originally open to the elements until 1934 when a the steel shield was added to give protection against splinters and small arms fire. The photo below shows the Mark of the shield.
A narrow channel descends to the entrance door of the underground magazine. The turntable which supports and rotates the gun is surrounded by concrete. Access to this area is via the large black steel doors seen behind and below the gun. The turntable enclosure also contains the upper parts of the shell hoist, you can view these as well as the turntable in item C in the map above.
The pathway leading downhill from the gun turns uphill to Lord Airey's Battery which can be seen at the top left of the photo above. The tops of the air vents above the underground engine room can be seen in the top centre of the photo. The entrance to the engine room is via steel doors adjacent to the point where the downhill slope turns uphill towards Lord Airey's battery.
The spare barrel sits along the path leading to Lord Airey's Battery.