Johnson grew up and was educated in the East Midlands, where he qualified as an engineer. A sportsman, Johnson broke his collarbone while playing rugby, an injury that later complicated his ambitions of becoming a fighter pilot. Johnson had been interested in aviation since his youth and applied to join the RAF. He was initially rejected, first on social, and then on medical grounds; he was eventually accepted in August 1939. The injury problems, however, returned during his early training and flying career, resulting in him missing the Battle of France and the Battle of Britain between May and October 1940.