In the early months of 1940, He 111s conducted raids against British shipping and naval targets in the North Sea before supporting the invasions of Denmark and Norway. On May 10, Luftwaffe He 111s aided ground forces as they opened the campaign in the Low Countries and France. Taking part in the Rotterdam Blitz four days later, the type continued to strike both strategic and tactical targets as the Allies retreated. At the end of the month, He 111s mounted raids against the British as they conducted the Dunkirk Evacuation. With the fall of France, the Luftwaffe began preparing for the Battle of Britain. Concentrating along the English Channel, He 111 units were joined by those flying the Do 17 and Junkers Ju 88. Commencing in July, the assault on Britain saw the He 111 encounter fierce resistance from Royal Air Force Hawker Hurricanes and Supermarine Spitfires. The early phases of the battle showed a need for the bomber to have a fighter escort and revealed a vulnerability to head-on attacks due to the He 111’s glazed nose.