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 war. His selected intercepts provided early insights into the French collapse during the Battle of France and proved crucial in the Battle of Britain, North Africa, El Alamein, and the D-Day invasion. The Ultra intelligence was vital for informing Allied military decisions, with Winston Churchill receiving urgent messages directly via a secure phone line.

By 1944, the system was highly efficient, delivering time-sensitive information, such as the rapid intelligence on the German evacuation of the Casino line in Italy. Winterbotham also analyzed the surprise of the 1944-45 Ardennes Offensive, noting that the absence of German signals should have raised alarms.

Winterbotham’s first-hand account of the Enigma program offers an unmatched perspective on its strategic importance.