After training, in August 1940, he was briefly posted to No. 19 Squadron as a probationary pilot officer. Due to equipment difficulties, 19 Squadron were unable to complete Johnson's training and he left the unit. On 6 September 1940 Johnson was posted to No. 616 Squadron at RAF Coltishall. Squadron Leader H.L "Billy" Burton took Johnson on a 50-minute training flight in X4055. After the flight Burton impressed upon Johnson the difficulties of deflection shooting and the technique of a killing shot from line-astern or near line-astern positions; the duty of the number two whose job was not to shoot down enemy aircraft but to ensure the leader's tail was safe. Burton also directed Johnson to some critical tactical essentials; the importance of keeping good battle formation and the tactical use of sun, cloud and height. Five days later, Johnson flew an X-Raid patrol in Spitfire X4330, qualifying for the Battle of Britain clasp.