 Quiberon Bay is a large anchorage, between Lorient and Saint-Nazaire on the southwest coast of the Brittany Peninsula, sheltered by the Quiberon peninsula and a line of small islands and containing four small ports.The Auray river drains into the bay near one of the ports, Locmariaquer, and has scoured a 3000-yard-long -deep pool just offshore, between 30 and 300 yards wide with nearly vertical sides.Operation Chastity would have seen the construction of floating piers in the pool, allowing large ships to tie up alongside, with bridges to carry the cargo and troops to the shore.