Adolf Galland
While recovering, Mertens was briefly appointed to command 1 Staffel of (Training Fighter Wing – East) in April 1944 until he assumed temporary command of I Gruppe Jagdgeschwader 3 and then joined the staff of Adolf Galland General of Fighter pilots. From November 1944 Mertens held posts within (Training Fighter Wing – East) and finally the operational training establishment of Jagdgeschwader 1.