One of the singular logistical achievements associated with the Normandy invasion was the gigantic artificial harbors, or "mulberries," that were designed, built, and transported to the landing beaches, which lacked the natural harbor facilities that would be vital to continued support of the invasion. Prefabricated in English ports, these "mulberries" and the artificial breakwaters (designed to prevent pounding by the sea) were laboriously towed across the Channel immediately after the invasion and assembled. They allowed deep-water Allied cargo ships to unload their cargoes quickly and efficiently. Also the LST's could do a quick turn around because they did not have to wait 12 hours for the tide to come in. A far larger amount of cargo moved ashore on artificial causeways.