An increased build-up of Soviet forces opposite Army Group Centre was largely ignored by Busch. Despite some of his subordinate's efforts to reduce their frontage, he refused to let them do so and blindly reiterated Hitler's orders that there be no retreat. In particular, the towns of Vitebsk, Orsha, Mogilev, and Bobruisk were to be held in force. Busch had attempted to query this with Hitler but was rebuffed and ridiculed. This only strengthened Busch's resolve to follow Hitler's directives without question. By mid-June, the 700,000 troops of Army Group Centre were outnumbered by 2,500,000 Soviet soldiers. When the Soviet summer offensive of 1944, Operation Bagration, began on 22 June, Army Group Centre's 34 divisions were overwhelmed by nearly 120 Red Army divisions. His army commanders immediately sought permission to withdraw to the Dnieper River but this was denied by Busch, who insisted their positions be held. Within two days, most of his divisions were effectively destroyed. Having overseen the loss of 250,000-300,000 men (25 full divisions), the biggest defeat for Germany on the Eastern Front, Busch was relieved of his command by Hitler on 28 June. He was replaced by Field Marshal Walter Model who managed to stop the advance of the Red Army, but not until it reached the Vistula. In the meantime, Busch became depressed after his sacking which effectively came about because of his adherence to Hitler's orders.