 On 19 September 1939, "Oberst" Osterkamp was appointed "Geschwaderkommodore" of Jagdgeschwader 51 (JG 51—51st Fighter Wing).During the Battle of France, he claimed four victories.During the "Kanalkampf" period of the Battle of Britain in July 1940, he claimed a further two victories, (a Bristol Blenheim on 1 June and a Spitfire on 13 July 1940) bringing his total to six.