On 12 September 1939 Commander-in-Chief of the "Luftwaffe" Hermann Göring visited the unit. I./KG 55 flew against target in the Dubno area on 15 September as operations wound down. On this date KG 55 flew 363 individual sorties. By the 20 September the number of sorties flown stood at 670. On the night of the 16/17 September "Luftflotte" 4 was ordered to stand down and cease operations as part of the Nazi-Soviet Pact. The Red Army invaded Poland the following morning. II./KG 55 was moved back to Giessen on 22 September. During the campaign KG 55 suffered one complete loss of aircraft and crew, in which an "Oberleutnant" Walter Fritz and his crew from 1./KG 55 were killed in action south west of L'vov.