Required:
Overy, Russia's War, pp. 73-153.

Suggested:
.David Glantz, Barbarossa: Hitler's Invasion of Russia, 1941 (Charleston, SC:Tempus, 2001).

John Erickson and David Dilks, eds., Barbarossa: The Axis and the Allies (Edinburgh: Edinburgh University Press, 1994).

Alexander Werth, Russia at War, 1941-1945 (New York: Dutton, 1964; London: 1985).