Frederick W. Winterbotham, 92, a group captain who played a key role in exploiting broken German codes in World War II and wrote the best-selling memoir “The Ultra Secret.” Winterbotham was a pilot in World War I, and in 1929 was made head of aerial intelligence in MI-6, the British intelligence agency. In the 1930s, he managed to befriend senior Nazi figures in Germany and gleaned information about the Luftwaffe. In 1939, he helped devise a vital new method of aerial reconnaissance photography. But his most important work was with “Enigma,” the top-secret German code system that the British had managed to penetrate. Winterbotham’s job was to get the information about “Enigma” to commanders in the field without revealing to the Germans that their code had been cracked. He worked out a system that was successful throughout the war and did not become public knowledge until the 1970s. His work made him a confidant of Prime Minister Winston Churchill. But he remained an unsung war hero, because the cracking of “Enigma” was considered so secret it was not revealed for 30 years after the war, when Winterbotham published “The Ultra Secret.” In London on Sunday.