Nazi Germany found itself at a logistical disadvantage, having failed to conquer the USSR with Operation Barbarossa (June-December 1941), the Siege of Leningrad (September 1941 - January 1944), Operation Nordlicht ("Northern Light", August-October 1942), and the Battle of Stalingrad (July 1942 - February 1943).
Overnight, Ph.D.s were liberated from KP duty, masters of science were recalled from orderly service, mathematicians were hauled out of bakeries, and precision mechanics ceased to be truck drivers.