On 26 October 1939, Bertram was appointed Staffelkapitän of 1./JG 2. Now an oberleutnant, Bertram claimed his first aerial victory of World War II on 20 April 1940, when he downed a Morane 406 fighter over Saint-Avold, flown by future French ace Sgt.
Bertram led 1./JG 2 during the opening phases of the Battle of Britain.