On 13 August 1940, during the Battle of Britain, Wilcke replaced "Hauptmann" Harro Harder as "Gruppenkommandeur" of the III. "Gruppe". Harder had been last seen at 1:35 pm on 12 August and was reported as missing in action following combat east of the Isle of Wight. The day of his appointment, Wilcke almost lost his life as well, when he was forced to bail out after engine failure over the English Channel. He was rescued that night by a Dornier Do 18 flying boat. III. "Gruppe" flew a bomber escort mission targeting London on 30 August. Wilcke destroyed a barrage balloon on the morning mission and claimed his fourth victory, a Supermarine Spitfire in the vicinity of Dover during his second mission of the day. On 1 September 1940, on another bomber escort mission that started at 11:20 am, Wilcke claimed his fifth victory, a Hawker Hurricane, south of London. He claimed his sixth victory, probably a Fairey Swordfish biplane, on 11 September over the Channel between Dover and Calais.