Such information enabled the Allies to build up an accurate picture of enemy plans and orders of battle, forming the basis of war plans both strategic and tactical. Ultra intercepts of signals helped the Royal Air Force to win the Battle of Britain in 1940-41. Resultant revelations of Japanese plans led to U.S. naval victories in the battles of the Coral Sea and Midway, crushing the offensive power of the Japanese fleet, and enabled American flyers to find and shoot down the plane carrying Admiral Yamamoto Isoroku, the Japanese commander in the Pacific. For 29 years after the war the existence of Ultra remained an official British secret. The ban was not lifted until 1974, the year that a key participant in the Ultra project, Frederick William Winterbotham , published The Ultra Secret.
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