Because the Allies knew the Germans would heavily defend or destroy major French ports, they brought their own. The Mulberry Harbours were two massive, pre-fabricated portable ports towed across the English Channel and sunk into place off the beaches of Normandy. They consisted of 'Gooseberries' (sunken old ships acting as breakwaters) and 'Whales' (floating roadways). They allowed the Allies to offload heavy tanks and thousands of tons of supplies every day directly onto the beaches. One was destroyed by a storm shortly after D-Day, but 'Mulberry B' at Arromanches operated for 10 months.