Barbarossa was the codename used by the Germans for the invasion of the USSR that began on 22 June 1941. Hitler had made his intentions towards the USSR clear in Mein Kampf; the vast plains of the USSR were to be conquered to provide Germans lebensraum (living space), and to ensure that Germany could never again be starved into submission as she had been in WWI. The strategy behind Operation Barbarossa was an extension of the blitzkrieg concept used to great effect in the Low Countries and France the previous spring – a quick strike at the heart of the USSR, in order to force surrender before the Russian winter set in.

At the beginning of the invasion of the USSR, German forces on the Eastern Front totaled more than 3.5 million men, 3600 tanks and 2700 aircraft, organized into three Army Groups – North, which struck towards Leningrad, Centre – which struck towards Minsk and Smolensk, and South – which struck towards Kyiv. The German forces were opposed by the Red Army, which totaled 2.9 million men, more than 10000 tanks, and about 8000 aircraft. However, Stalin had ignored repeated warnings from both his intelligence services and British sources that an attack by Germany was imminent. As a result, the Red Army, ill prepared, was routed in the first weeks of the invasion. Almost all her air force was destroyed, and through the summer the Wehrmacht swept through the Western regions of the USSR.

It was only at the gates of Moscow in December 1941 that the Wehrmacht suffered its first serious setback of the War. Having advanced to within a few dozen miles of the Soviet capital, the Wehrmacht, overextended and ill supplied for fighting in the extremely cold conditions, was repelled by a massive Soviet counteroffensive. Although the Front was eventually stabilized, Operation Barbarossa and the attempt to force a Soviet surrender before winter, had failed. After December 1941 time worked against the German forces, as the combined economic might of the USSR and the USA, which had entered the War on 7 December 1941, far outweighed the German ability to produce materiel for the war effort. In 1942, Germany switched strategies; instead of attempting to quickly capture Moscow they focused their spring and summer offensives to the south, in an attempt to capture the vast oil reserves of the Caucuses.