D-Day, 6 June 1944, the turning point of the Second World War, was a victory of arms, a heroic feat of military strategy and raw courage. But it was also a triumph for a different kind of skill: it was an astonishing feat of paperwork.
Operation Fortitude, which protected and enabled the invasion, and the Double Cross system, which specialized in turning German spies into double agents, deceived the Nazis into believing that the Allies would attack at Calais and Norway rather than Normandy. It was the most sophisticated and successful deception operation ever carried out, ensuring that Hitler kept an entire army awaiting a fake invasion, saving thousands of lives, and securing an Allied victory at the most critical juncture in the war.
The Double Cross system depended on a filing and archive system that was vast, complex and meticulous. It is not too much to say that without the extraordinary record-keeping system devised by the spy-runners, the great D-Day deception might have failed, and the history of the 20th century would have been very different.
The great British talent for keeping and maintaining records played a vital, but largely unacknowledged role in winning the Second World War. Most of the wartime files relating to the Double Cross deception, once top secret, have now been released to The National Archives. That material has formed the evidential basis for my last three books: Agent Zigzag, Operation Mincemeat and Double Cross. Each of these books tells a story extracted from the wartime files. Indeed, without this huge trove of documents, these books could not have been written.