At about 0100 hours, the Red Army was ordered to assume defensive posture, but it was too late to improve defenses significantly as Germany tore up the non-aggression pact and launched Operation Barbarossa. At 0325 hours, Georgy Zhukov woke Joseph Stalin by phone to inform him of the news of the invasion; initially, Stalin refused to give Zhukov the permission to strike back at the Germans, believing it to be a German provocation. At 0630 hours, Stalin finally realized it was a full scale invasion and gave his authorization for the Red Army to fire back. At a strength of 3.5 million men, Operation Barbarossa was the largest military operation in history, overwhelming Soviet defenses which were further disadvantaged by poor communications. In support, German aircraft destroyed 2,000 aircraft, many on the ground, allowing the Germans to gain air superiority across the entire front
