Then in late May the Allies also confirmed that BdU had cracked the British naval cypher, and had been intercepting communications with convoys at sea for months. This had enabled Doenitz and his men to intelligently guide the wolfpacks toward convoys. Realising the exposure, the US and British navies switched to a newer code, known as Naval Cypher No. 5–once again blinding Doenitz and the U-boats.
