He was transferred to the Flying Training School at Penfold, Alberta in 1942, and then to the Mosquito Conversion Unit at Greenwood, Nova Scotia, 1943–1944.
He then joined 21 Squadron[2] of 140 Wing, RAF Hunsdon, flying Mosquitoes on night fighter intruder missions over Nazi Germany.
Horsley then was attached to the communications squadron of the 2nd Tactical Air Force in France, and was personal pilot to Major-General Miles Graham during the Normandy invasion.
[2] Horsley attended the Imperial Defence College, and was then appointed Deputy Commandant at the Joint Warfare Establishment at Old Sarum in Wiltshire in 1966.
[2] Horsley had a number of business interests after retirement from the RAF: Robson Lowe (stamp auction house), chair; Stanley Gibbons, managing director.
He wrote an autobiography, Sounds From Another Room (subtitled Memories of Planes, Princes and the Paranormal), published Leo Cooper in 1997, which described his interest in UFOs, which began when Equerry to His Royal Highness the Duke of Edinburgh, and a close encounter with an "alien" in London in 1954 [citation needed] .