Johnson's old injury continued to trouble him and he found flying high performance aircraft like the Spitfire extremely painful. RAF medics gave him two options; he could have an operation that would correct the problem, but this meant he would miss the Battle of Britain, or becoming a training instructor flying the light Tiger Moth. Johnson opted for the operation. He had hoped for discreet treatment, but word soon reached the CO, and Johnson was taken off flying duties and sent to the RAF Hospital at Rauceby. He did not return to the squadron until 28 December 1940. CO Burton took Johnson up for a test flight on 31 December 1940 in Miles Magister L8151. After the 45-minute flight, Johnson's fitness to fly was approved.