Operation Barbarossa was the code name for Nazi Germany's invasion of the Soviet Union, launched on June 22, 1941. It was the largest military operation in history, involving over 3 million German troops along a 1,800-mile front. Initially spectacularly successful, the operation ultimately failed to achieve its objectives and became the turning point of WW2 in Europe.
The invasion caught the Soviets largely by surprise despite numerous warnings. German forces conquered vast territories and captured hundreds of thousands of prisoners. However, tenacious Soviet defense, the vast distances, and the onset of the Russian winter prevented the capture of Moscow by year's end.