After June 22, 1941 the Soviets would not have fought the war completely on their own, but allied with the British Empire. A British air squadron sent to Murmansk was essential to keeping the port open to receive US and UK aid shipments (https://en.wikipedia.org/wiki/No._151_Wing_RAF ). However, a delayed US entry into the war against Germany would have delayed, though not changed, the final outcome. Delaying this outcome might have made Germany instead of Japan an atomic weapons target.