During his summit with Churchill and Roosevelt In Tehran at the end of 1943, Stalin promised to launch a major offensive to coincide with the Allied invasion. Operation Overlord went forward on June 6, and Stalin launched his own attack, Operation Bagration (named after a czarist general), on the 22nd, the third anniversary of Hitler’s invasion of Russia. The invasion force consisted of 1,700,000 troops supported by 6,000 aircraft, nearly 3,000 tanks, and 24,000 artillery pieces. This attack destroyed Army Group Center and was the most disastrous defeat suffered by the Germans in the war, costing the Wehrmacht more men and material than the defeat at Stalingrad. Within a matter of weeks afterward, the Red Army reached Warsaw in what became an inexorable march toward Berlin.
Click to see Operation Bagration map.