Arromanches — Mulberry Harbour

With no captured port available, the Allies built their own: two vast prefabricated 'Mulberry' harbours were towed in sections across the English Channel and assembled off the Normandy coast within days of D-Day. Mulberry 'B' at Arromanches, protected by sunken blockships and concrete caissons called Phoenixes, unloaded some 2.5 million men, half a million vehicles and 4 million tonnes of supplies before winter. A June storm wrecked the American harbour at Omaha, but Arromanches endured for months. At low tide the rusting caissons still loom offshore—a colossal feat of engineering that kept the liberation of Europe supplied.