Gun Island is one of the larger islands in the Pelsaert Group of the Houtman Abrolhos, in the Indian Ocean off the west coast of Australia. It is nominally located at (28°53′10″S113°51′35″E), about 4 km north and east of Half Moon Reef and is a flat limestone outcrop of about 800 metres (2,600 ft) by 420 metres (1,380 ft) in size.