In June 1941 three million Germans stormed into Russia, the largest military invasion in history. The Russians lost 4,500 aircraft – half their air force – and 20,000 tanks in the first nine days. The Germans marched to within 15 miles of Moscow. Stalin was screaming at Churchill for aid. The Allies agreed to send aid to Russia by means of convoys every ten days from USA and UK by the shortest route - via the ferocious freezing North Sea to Murmansk in North Russia. The first few convoys sailed through without much damage - until the Germans decided to attack.