Operation Iron Ring

'Iron Ring' was a British submarine blockade of Brest on the western tip of Brittany in German-occupied northern France in an effort to intercept, attack and destroy German warship raiders, most notably the battle-cruisers Scharnhorst and Gneisenau, the pocket battleship Admiral Scheer and the heavy cruiser Admiral Hipper as these warships returned from commerce-raiding forays, such as 'Berlin' (i), into the Atlantic (March 1941).