(53) German WW 2 Feldpost cover from the Rechlin Luftwaffe air force base company postmarked December 5, 1940.

This was sent by a Feldwebel who was attending a type of K.O.N. course. 

Rechlin was THE test- and evaluation center of the German Luftwaffe = Air Force, from the end of WW1 to the end of WW2. From Fokker to Focke-Wulf may say, both Hitler and Goering were frequent visitors to see the latest in German aircraft being tested. (53)