By the spring of nineteen forty three, the Allies had cleared North Africa and everyone understood what came next. They would cross the Mediterranean into southern Europe, and the obvious place to land was Sicily.
It was so obvious that Churchill said anybody but a fool would know it was Sicily.
Which is a serious problem, because an island that is expecting you is an island covered in guns.
So a small group in London was given a question that sounds impossible: how do you persuade an enemy that the obvious thing is not going to happen?
The group was tiny and it worked in a basement under the Admiralty. The two who mattered most were Ewen Montagu, a barrister in naval uniform, and Charles Cholmondeley, an air force officer with poor eyesight and an unusually strange imagination.
They kept a list of ideas for deceiving the enemy. Most of them were terrible. One of them, number twenty-eight, was a suggestion that a dead body carrying false documents might be dropped where the enemy would find it.
The difficulty is that nobody believes a gift. If a body full of secret plans washes up, the natural conclusion is that somebody wanted it to.
So the operation was not really about the documents. It was about building a person convincing enough that the documents came along for free.
They needed a body, and here the story stops being clever and becomes sad.
The man they used is now generally accepted to have been Glyndwr Michael, a Welshman of thirty-four who had been living rough in London and who died after swallowing rat poison. He had no family anybody could find. He had done nothing, and had nothing, and the state took his body because nobody would ask for it.
They made him into Major William Martin of the Royal Marines.
Then they filled his pockets, and this is where the operation becomes a piece of craft. A wallet with a photograph of a fiancée called Pam, who was in fact a clerk in the office who agreed to lend her picture. Two love letters from her, one of them slightly cross about him going away. A letter from his father, stiff and disapproving. A bill from a shirtmaker. A receipt for an engagement ring, expensive enough to be worrying.
And a letter from his bank, in a tone of some irritation, about an overdraft of seventy-nine pounds.
Also two ticket stubs from a London theatre, dated a few days before, which quietly proved he had been alive and in London until very recently.
The actual documents were a private letter between two generals, written to sound casual, which mentioned in passing that the target was Greece, and made a small joke about sardines that was intended to hint at Sardinia.
He was carried to Scotland in a steel canister packed with dry ice, put aboard the submarine Seraph, and taken to the coast of Spain.
Spain was neutral and was also, in practice, cooperative with German intelligence, which is precisely why it was chosen. A body found by the Spanish would be examined and the contents would reach Berlin, while the British could publicly ask for the papers back and appear anxious, which made them look genuine.
He was put into the water off Huelva on the thirtieth of April, nineteen forty three, at a spot chosen because the tide there would carry him ashore. The submarine's crew, who had been told they were carrying a meteorological device, said a short service over him first.
It worked completely. Copies of the documents reached German intelligence within a fortnight. They were assessed as genuine. The German high command concluded that the Mediterranean landing would come in Greece.
Divisions were moved to Greece. Minefields were laid off Greek beaches. A general was sent to take command there. Reinforcements bound for Sicily were held back.
The Allies landed in Sicily on the tenth of July and got ashore against much lighter opposition than anyone had dared expect.
The same idea was then run again, on a scale that is hard to picture, before the landings in Normandy.
Everybody knew an invasion of France was coming. The question was where, and the shortest crossing, and therefore the obvious answer, was the Pas de Calais.
So the Allies built an army there. On the English coast opposite Calais they created the First United States Army Group, and it did not exist.
It had inflatable rubber tanks that two men could carry and one man could inflate. It had landing craft made of painted canvas over scaffolding, moored in harbours. It had dummy oil storage depots, built by film set designers, that were convincing from the air and about an inch thick. It had tracks driven into fields by a single vehicle going back and forth to look like a division.
Most importantly it had radio. A handful of operators generated the volume of chatter that a whole army group produces: routine orders, supply requests, complaints, unit call signs, all of it real-sounding and all of it invented.
And it was given a commander whose presence alone was evidence. General George Patton, whom the Germans regarded as the best they faced, was placed in charge of an army made of rubber.
The last piece was a man called Juan Pujol Garcia, a Spaniard who disliked fascism and decided, entirely on his own initiative, to become a spy against Germany.
He offered his services to the British, who turned him down. So he went to the Germans instead, was accepted as an agent, and was sent to Britain. He did not go to Britain. He went to Lisbon, and from there he invented reports about a country he had never visited, using a tourist guide, a railway timetable and a magazine about the cinema.
His reports were good enough that British intelligence, intercepting German traffic, began hunting for the dangerous spy who was producing them. When they finally worked out what was happening they took him on and moved him to London, where he was given the codename Garbo.
He then constructed an imaginary network of twenty-seven sub-agents across Britain, all of them fictitious, all with personalities and expenses, and Germany paid the salaries of every one of them.
His masterpiece came after D-Day had already begun. He sent a message insisting that Normandy was a diversion and the real blow would fall at Calais. It was believed. German armoured divisions that could have counter-attacked in Normandy were held in place for weeks waiting for an invasion that did not exist.
Pujol finished the war with a German Iron Cross and a British MBE, which is very likely a unique combination.
Glyndwr Michael's name was not on his grave for fifty-five years. He was buried in Huelva under the name of Major William Martin, and in nineteen ninety eight the British government added a line to the headstone recording that the man buried there was Glyndwr Michael and that he served as Major Martin.
It is worth pausing on that. A man nobody wanted, who died alone, was used without his knowledge or consent, and the use of him saved a large number of lives on a beach he had never heard of. There is no tidy way to feel about it, and it is better not to try.
The theatre tickets are the detail professionals still admire most. Everything else in the wallet proved who he was. The tickets proved when he was, which is a far harder thing to fake and the question nobody expected to be answered.
Here is something to think about tonight. Every one of these tricks worked by giving the enemy exactly what he already suspected. Nobody was persuaded of something surprising. They were confirmed in something comfortable. Which do you think is easier to sell somebody, a new idea or their own?