Initially flew with 254 Squadron - flying Blenheims – having completed his trained as an observer in 1940. Finding flying coastal and convoy patrols tedious he answered a request for volunteers for ‘special duties’. Was sent for training as a navigator on night fighters. In June 1942 joined 85 Squadron who were equipped with Havocs. During his time with 85 Squadron Cairns and his pilot downed a Dornier bomber. Cairns was then sent on a rest tour – became a founder member of the Blind Approach Development Unit at Watchfield. In November 1943 he joined 488 Squadron – the squadron’s Mosquitos had just been fitted with AI (airborne interception) radar – his pilot was John Hall. In late January (21st/22nd) 1944 Cairns brought Hall to within visual range of a Dornier 217 which Hall then downed. As the Dornier fell out of the sky a Junkers 88 was spotted coned in some searchlights. The Mosquito gave chase and forced the Junkers in to the sea. In March 1944 Hall/Cairns downed a Junkers bomber. In the lead up to the Normandy invasion, the Mosquitos of 488 squadron flew night intruder sorties over northern France. After shooting down their fifth aircraft in June 1944 both Hall and Cairns were awarded the DFC. In November 1944 488 Squadron moved to Amiens. By the end of their tour with 488 Squadron Hall/Cairns had shot down eight enemy machines. John Cairns visited New Zealand in the 1990s to attend a squadron reunion.