 After obtaining his RAF wings, Pilot Officer Garrison was shipped to England, where after further training he was promoted to Flying Officer and made a gunnery instructor, posted to RAF Hawarden to train pilots flying North American Mustangs.On July 13, 1943, Garrison transferred from the RAF to the United States Army Air Forces, receiving a commission as a first lieutenant.On September 26, after transition training in the P-47 Thunderbolt at RAF Atcham, he was assigned to the 4th Fighter Group, based at RAF Debden, as a member of the 336th Fighter Squadron.