Axis foces invade USSR June 1941; Wikimedia Commons

Using the codename Operation Barbarossa, Axis forces totaling 3 million men from Germany, Italy, Romania, Hungary and Finland launched a surprise attack against the USSR along a 2000 mile front on June 22, 1942.

Although Britain and the United States were wary of Stalin, Britain began providing the USSR with intelligence on German activity and intensified the bombing of major German cities. Soon, both Britain and the USA shipped many aircraft, tanks, food and medical supplies to the USSR.