When the Korean War broke out on 25 June 1950, No. 77 (Fighter) Squadron of the Royal Australian Air Force (RAAF) was based at Iwakuni, Japan. For the previous four years the squadron, equipped with North American P-51 Mustangs, had served with the British Commonwealth Occupation Force (BCOF). Personnel were preparing to return to Australia when they were placed on standby for action over Korea; the squadron began flying missions as part of United Nations (UN) forces a week later. Following the landing at Inchon and the consequent advance northward of UN troops, No. 77 Squadron relocated to Pohang, South Korea, on 12 October 1950. It left behind its main support elements at Iwakuni. No. 91 (Composite) Wing was established at the base on 20 October and given administrative responsibility for all RAAF units operating during the conflict. This included No. 77 Squadron and three newly formed components: No. 30 Communications Flight (renamed No. 30 Communications Unit the following month, No. 30 Transport Unit in November 1951 and No. 36 (Transport) Squadron in March 1953), No. 491 (Maintenance) Squadron, and No. 391 (Base) Squadron. Apart from No. 77 Squadron, the wing's units were all headquartered at Iwakuni.