All three group flew as bomber formations against the Soviet summer offensive, Operation Bagration. "Luftflotte" 6, to which KG 55 was attached, deployed the unit on the central sector supporting Army Group Centre. It had 107 Heinkel He 111s on 26 June, with stab./KG 55 possessing a single bomber. I./KG 55 used 35 in night operations in support of Army Group North over Lithuania. It flew night attacks and some supply mission from 23 June–4 July. By 27 July it had retreated to Tonndorf, southwest of Bydgoszcz. It converted to H-20 models and flew missions against the Lvov–Sandomierz Offensive and bridges across the Vistula, near Warsaw and was based at Baranów Sandomierski, from 28 July–12 August 1944. In late August it left for Bavaria, Germany. There it had 31 He 111s (25 H-20s). It moved to Straubing, in September and was renamed I./KG(J) 55 and began converting to a fighter unit on 1 October.