Vilnius Offensive

On June 22, 1944, the Soviets launched their main summer offensive (Operation Bagration) in Belarus. Involving 2.5 million soldiers and over 6,000 tanks, the offensive sought to destroy Army Group Center while also preventing the Germans from diverting troops to combat the Allied landings in France. In the ensuing battle, the Wehrmacht suffered one its worst defeats of the war as Army Group Center was shattered and Minsk liberated.

http://militaryhistory.about.com/od/worldwarii/...