The capture of a fully functional five rotor Enigma machine off of U-110 in early May, 1941 allowed Bletchley Park to read the German Kriegsmarine operation’s orders within days, and sometimes hours after they were transmitted.
The first use of the newly available intelligence windfall were the locations of all of the German tankers and supply ships that U-boats used to replenish without going back to port. Between 2 and 5 June 1941, four Norwegian and Danish flagged tankers, and two freighters packed with torpedoes and food were sunk. The lost ships so upset the German rotation that the operation was the equivalent of sinking 30 U-boats. The British let slip to a known German double agent that the ships were identified due to the preponderance of search assets in the Atlantic because of the Bismarck, and a spy in the Kriegsmarine Headquarters.