In WWII Graemsay Battery was armed with a twin six-pounder gun. Mounted at the Point of Oxan, it provided anti-MTB (Motor Torpedo Boat) defence for Hoy Sound.
The gun had been emplaced at Northfield on the north end of Burray, but was moved to Graemsay in 1943 after the construction of the Churchill Barriers made the presence of anti-ship defences unnecessary there. The gun was mounted at the Point of Oxan before the end of 1943, but was not fully operational until March 1944. The twin-six pounder could fire 72 rounds per minute and was designed to take on fast moving craft such as MTBs.
The nearby searchlight emplacements housed four 15kW Fortress Mk VI projectors which emitted dispersed searchlight beams, overlapping to form a wide illuminated area. There were further lights along the shore near Stromness to the north and at Skerry Battery on Hoy to the southwest, and between them they would have been capable of turning night into day should any hostile vessel try an attack.
With another twin-six at Links Battery near Point of Ness, the two six-inch guns nearby at Ness Battery and the pair of 12-pounders at Skerry Battery on Hoy, a vessel trying to enter through the mouth of Hoy Sound would come under a combined fire of up to 190 shells per minute.