Before the D-day invasion,The invading Allies realized that the harbors would be either extremely heavily guarded, or would be destroyed by the retreating German army. Since harbors are necessary for large-scale import of war materials, the Allies brought their own. Concrete sections, called "mulberries", were constructed in England, floated into position and sunk to form an artificial harbor. This allowed the off-loading of materials before Cherbourg was accessible to the Allies. What remains of the harbor is shown here.