As the Allies broke out of Normandy in June 1944 and pushed into France and the Low Countries they soon found that their supplies lines became more and more extended. They needed a proper working port on the Channel that would enable them to bring in more men and materiel to fight the Germans in Europe and alleviate their supply issues. 

Antwerp was the prize they were after but the Germans had it covered so other ports needed to be captured as a matter of urgency. 

This is the story of the capture of Dieppe, Le Havre, Boulogne and Calais and the Siege of Dunkirk that the Allies decided to do while they concentrated on capturing and bringing only the port of Antwerp. It was a siege that was to last until the end of the war.