In preparation for Operation Marita, the German invasion of Greece, III. Gruppe of JG 77 was moved to Deta in western Romania on 4 April 1941. Ubben claimed a No. 33 Squadron Hawker Hurricane fighter near Larissa on 19 April, although his Bf 109 E-7 (Werknummer 5198—factory number) was badly damaged in the engagement and Ubben forced-landed behind Allied lines near Doblatan. He was rescued by a Fieseler Fi 156 Storch and flown back to his unit. No. 33 Squadron claimed four Bf 109s during the battle, though only three were brought down. Among the claimants was RAF ace Marmaduke Pattle, who claimed two Bf 109s shot down. Ubben may have been one of his victims. III. Gruppe followed the German advance and relocated to Almyros on 22 April and to Tanagra on 27 April. The conquest of Greece was completed on 30 April and JG 77, starting a brief period of rest and maintenance for JG 77.
