Operation Barbarossa was a major German military operation executed from 22 June to 5 December 1941 when 3,000,000 German troops, 3,580 tanks, 7,184 artillery pieces, and 2,000 aircraft launched a massive invasion of the Soviet Union. The invasion had been planned out since 1940, with the German dictator Adolf Hitler seeking to destroy the Bolshevik USSR and exterminate the Slavs, Jews, communists, and "Asiatics" of the Soviet Union. The attack took the Soviets by surprise, as the Soviet dictator Joseph Stalin ignored British intelligence warnings about the German preparations for an invasion.
The Germans began the invasion by using their Luftwaffe air force to destroy the Soviet Air Force on the ground, destroying 25% of the air force (1,600 planes). The Soviets in Brest-Litovsk and Bialystok were encircled on 26 June 1941, and tens of thousands of troops were captured in "cauldron battles". The German Army Group Center's two panzer armies pushed on Minsk, and the German panzer spearheads covered 50 miles a day during the rapid advance into Russia. The Germans encircled Minsk and captured 324,000 Red Army troops at the end of June, and Army Group Center's panzer groups advanced across the Dnieper on 1 July before capturing 300,000 Red Army troops, 3,205 tanks, and 3,120 guns after encircling and capturing Smolensk on 16 July. However, heavy rains began to slow the German advance, and the Germans began to lose 1,000 horses (out of 750,000) every day. By mid-August 1941, there were 500,000 German casualties. Army Group Center had to halt to bring up supplies, as tank strength had fallen by half, and ammunition was running low.
On 21 August 1941, Adolf Hitler took command of the war effort in the east, and he issued a directive that shifted the emphasis to southern Russia and the Ukraine. He sent a panzer group to aid Army Group South in an encirclement in northern Ukraine, while another one assisted the advancing Army Group North in the Baltics; Army Group North had Riga on 1 July and began to encircle Leningrad on 1 September. Stalin orered his troops to stand still and fight, leading to 665,000 Red Army troops being taken prisoner in Kiev on 19 September 1941. Stalin blamed the defeat on his generals and became the new commander of the Stavka, the Soviet high command. Hitler decided to make the Siege of Leningrad the new priority, and the Germans and their allies from Finland would proceed to starve the city out; 300 people died every day in the city during October. Hitelr decided to again focus on the drive on Moscow, and he refused to halt the advance as Gerd von Rundstedt had advised. Army Group North's panzer spearhead joined Army Group Center for the push against Moscow, with Heinz Guderian commanding the push on Moscow. The Germans opened the drive on Moscow on 30 September 1941, and the Germans captured 600,000 German troops west of Vyazma and Bryansk a week later, some nine Soviet armies.
By October, snow had fallen during the rasputitsa heavy rains, and the Germans suffered from the pitiless climate. Few German troops had warm clothes, so they had to strip dead Soviet soldiers of their clothing to keep themselves warm. By the end of October, the Germans were 40 miles from Moscow, and Stalin appointed Georgy Zhukov as the new commander of the Soviet forces on the front. Fresh divisions were transferred to Moscow from Siberia after the Soviets discovered that Japan had no intention of joining Germany in the war, and the Soviets prepared to fight in the winter. By 27 November, the Germans had reached the Volga Canal, 20 miles from Moscow. On 5 December 1941, the German forward units were pulled back from the canal, and the two sides prepared for the upcoming Battle of Moscow.
The Germans acknowledged that the war would be long, and that there would not be an easy victory. The Germans had lost 743,000 men (not counting ill soldiers), while the Germans were short of 340,000 troops, 50% of the fighting strength of their infantry. Only 33,000 men could be called to replace those lost during the invasion, and only 50,000 German trucks remained out of the 500,000 that had started the campaign (150,000 had been written off and 300,000 were in need of repair). The Soviets, meanwhile, had lost nearly 3,000,000 killed in action, while 3,500,000 Soviet troops were captured during the bloody campaign. Despite heavy losses, the Soviets were still ready to fight against the Germans in the winter, and they would launch a major counterattack.