Who spilt the beans? How the Enigma secret was revealed

Although the secret was kept for nearly 30 years after the end of WW2, it’s now nearly 50 years since the public was told that the Allies had broken literally millions of Enigma-encrypted messages during the war, providing a wealth of authentic Intelligence about German military plans, reactions, state of readiness, and so on. Miraculously, the eleven thousand women and men who worked at Bletchley Park and in its outstations had understood the need for total silence, and had told no-one, not even close family.

Looking back, we can actually detect tiny fragments of the story creeping into books published as early as the late 1950s, but none of these told of the scale or importance of Bletchley’s successes. It was in 1974 that Weidenfeld & Nicolson published The Ultra Secret by Frederick Winterbotham. He had not been a codebreaker, but had headed up the RAF’s Intelligence section since 1930, and was well aware of the significance of what the codebreakers had achieved. He also devised the technique whereby the Intelligence generated by the codebreakers could be delivered totally securely to Allied commanders in the field. The book, published simultaneously in UK and USA, caused a sensation, was much reprinted, and sales soon passed the million mark. Journalists loved it, but historians were more cautious.

Winterbotham had requested, and received, official permission to write his book, but was given no access to the several hundred thousand relevant documents, which were, at that time, tightly locked away in GCHQ. He had, it appears, no diaries, so relied on memory alone, and made no reference to any sources, archival or published. The style of the book clearly reveals that it is not a scholarly work, and it must therefore not be taken as reliable. Its broad theme – that at Bletchley vast numbers of German wireless messages were broken, providing invaluable Intelligence which shaped Allied strategy – is indisputably correct, but the book contains, not surprisingly, serious errors, distortions, and omissions. One reviewer noted sadly that Winterbotham ‘has let out a big secret, but has failed to write a good book’.

Certain historians, noting that the book had been scrutinised by the D-notice committee, MI6, GCHQ, the Foreign Office, and even the Prime Minister, Harold Wilson, made the erroneous assumption that this scrutiny implied official endorsement of its contents. In this they were wrong; the official scrutiny was to ensure that nothing too sensitive was being revealed. It was not an official stamp of approval to say that everything in the book was correct.

One of the most pervasive errors is Winterbotham’s assertion that the city of Coventry was deliberately left undefended on 14 Nov 1940, because Churchill feared that defending it against a coming German bombing raid might have led the Germans to deduce that we were breaking Enigma-enciphered messages. Detailed analysis of surviving documents (not made available to Winterbotham) shows this to be completely untrue. It is, however, such a gripping idea that it has taken hold most tenaciously in the public mind. One American edition of the book even headlines in red on its rear cover ‘The secret that was worth sacrificing a whole city for’. When the truth is less exciting than the lie, the truth struggles to be heard.

The Ultra Secret is an important book because it was the first to prise open the door into the secret world of Bletchley Park and Enigma. It broke new ground, and forced a re-assessment of many WW2 events. It is a great read, so enjoy it, but if you want the true history, turn instead to the books that followed Winterbotham’s enterprising lead.