In April 1940, when British cryptographers at Bletchley Park decrypted some German air force messages, Group Captain Frederick Winterbotham recognized the potential of such intelligence and established a secure system to handle it. He created Special Liaison Units, small teams of RAF officers and enlisted men, to receive and securely distribute decrypted Ultra messages to relevant commanders. These messages, transmitted through encrypted radio signals, were kept highly classified, with recipients unaware of their origins. Winterbotham's units played a critical role in key moments during the...