After the armistice with France, Becker was transferred to the 2.(J) "Staffel" of "Nachtjagdgeschwader" 1 (NJG 1–1st Night Fighter Wing), initially based at Düsseldorf and Gütersloh, and then to Arnhem-Deelen airfield where he was appointed technical officer. Becker flew his first aerial combat mission on 30 August 1940. The mission resulted in the loss of the aircraft near Winterswijk, while he and his radio operator managed to save themselves with the parachute.