World War II in Europe began on Friday 1 September 1939 when German forces invaded Poland. Ehrler, who was still serving with the anti-aircraft artillery, requested transfer to the fighter force of the Luftwaffe on 3 January 1940.[Note 1] His transfer request was accepted and he underwent flight training from 1 February to 4 November 1940. During this training period he was promoted to Feldwebel (staff sergeant) on 1 July and to Leutnant (second lieutenant) on 1 January 1941.[3]