Which is OK. Late production Mk.Ia in the R6###, R7### & X4### serial number range (completed between May 1940 and April 1941) and AR2## (from July 1941 to January 1942) saw the introduction of constant speed DeHavilland propellers and armour plates behind the pilot’s seat & headrest (which were retrofitted to earlier production aircraft) as well as engine driven undercarriage retraction.
