During the summer of 1940, the German high command was putting Operation Sea Lion, the plan to invade Great Britain, into action. Ariel battles were fought over the Channel as the Luftwaffe fought for superiority in the air. Boulogne, Calais and many other areas along the north-east coast were subject to heavy bombardments. Huge artillery cannons, including the 420mm Big Bertha were used along the north coast before being moved to Sevastopol, where the German army required them in their struggle to hold the Eastern Front (the war against Russia). Throughout the summer, heavy artillery and munitions passed through Rue.