I have just seen a replica of Johnsons first spitfire on tv, JE J (EN398) and I photographed his third last year at Duxford.

Quote: As is widely known, Johnson scored the bulk of his victories flying two Spitfires Mk. IX. The first one was EN398, JE-J, (mk IX) the subject of this article, in which he shot down 12 aircraft and shared five plus six damaged while commanding the Kenley Wing. His second mount, MK392, was an LF Mk. IX, in which his tally increased by another 12 aircraft plus one shared destroyed on the ground. His last victory of the war in September 1944 was scored in the latter aircraft. He ended the war flying yet another Spitfire, Mk XIVe, MV268. As a Wing Leader Johnson was entitled to personal code letters and his aircraft were always marked JE-J. Unquote.

http://spitfiresite.com/2010/04/johnnie-johnsons-spitfire-revisited.html