Considering the very large number of twentieth century historians who participated in the Second World War, and had been indoctrinated into secret intelligence sources, it is astonishing that the true impact of intelligence on the successful prosecution of the conflict was not documented very much earlier. In fact the first mention of the contribution of Allied code-breaking in the Battle of the Atlantic and the defeat of the U-boats did not occur until 1968, and the vital role played by cryptoanalysts at Bletchley Park was not revealed for a further six years. Historians of the calibre of Sir Harry Hinsley, Hugh Trevor Roper and Ronald Lewin, who knew all too well about what has often been called ‘the missing dimension’ opted for discretion, and even David Kahn’s Codebreakers, released in 1966, omitted any reference to the German Enigma cipher machine. Understandably Winston Churchil’s magisterial account of The Second World War could not have been expected to disclose secrets, but the result was that, fed on a diet of sanitised biographies of Eisenhower and Montgomery, the public was given no clue about the wartime contributions made by Britain’s secret agencies.
Gradually, the truth began to emerge. After Fred Winterbotham received official permission in 1973 to write The Ultra Secret in an effort to stymie Anthony Cave Brown’s Bodyguard of Lies, and Sir John Masterman had released The Double Cross System in 1972, exposing the extent of MI5’s domination of its Abwehr adversary, the walls of secrecy in Whitehall began to crumble. The Foreign Secretary, David Owen, gave permission in 1977 for veterans of ULTRA to discuss the application of their special skills, but not to explain precisely how they had achieved technical mastery of the enemy’s cipher systems. Finally, the entire five volumes of the official history of British Intelligence in the Second World War were published, seven years after they had been commissioned in 1972, but the last volume, written by Sir Michael Howard, was held up for ten years before it was declassified in 1990.
Why the reluctance to impart the very significant influence of intelligence over the momentous events of the last century? Intelligence was crucial throughout the First World War, and Nigel de Grey’s breaking of the Zimmermann Telegram in 1917 has been widely regarded as a turning-point in the conduct of the war, and perhaps the one single event that propelled the United States into the conflict. Is it simply that espionage, cryptography and strategic deception have not been considered respectable subjects for study by bona fide historians, or is it that weapons of such potential should