A sardine fisherman working the water off Huelva on the morning of 30 April 1943 pulled in the body of a British officer. Battledress, life jacket, briefcase chained to his coat, several days at sea in him. Everything about the man added up: his name, his rank, his unit, his fiancée, his unpaid bills. Not one detail was true.

He was Glyndwr Michael, a homeless Welshman from Aberbargoed who had drifted to London and died there in January after ingesting rat poison. In its account of the operation, the Commonwealth War Graves Commission records that his father had taken his own life, his mother was dead, and nobody came looking for him. That last part was the whole point.

Item 28 on a list of dirty tricks

It began as a memo, and not a very serious one. In September 1939, Ian Fleming, a naval intelligence aide two decades away from inventing James Bond, helped compile fifty-one suggestions for planting ideas in German heads. Number 28 arrived flagged as unpleasant by its own authors: float a corpse dressed as an airman towards a hostile coast, pockets stuffed with dispatches, and let the enemy assume a parachute had failed. Writing in The Times of Israel, Robert Philpot notes the memo also claimed, quite wrongly, that corpses were easy to come by at the naval hospital.

Nobody touched the idea for three years.

Charles Cholmondeley, a 25-year-old RAF officer seconded to MI5, dug it out in 1942 and took it to Ewen Montagu, a barrister turned naval intelligence officer. By early 1943 they had a use for it. Sicily was the next Allied target and everybody could see it, Churchill included, which is the trouble with obvious plans. The Germans would pack the island with troops and wait.

Getting hold of a body was the hard part

Fleming had been optimistic about the supply. When Montagu asked Bentley Purchase, a coroner friend in north London, for a corpse to use in a warlike operation, Purchase told him flatly that you cannot get dead bodies just for the asking. Every one had to be accounted for. Once Purchase learned Churchill had personally approved the plan he grew more accommodating, and Michael duly arrived on his slab. Rat poison, he predicted, would leave little trace to contradict a story about a plane going down.

A man assembled from receipts

Michael became Captain, acting Major, William Martin of the Royal Marines, and the next few weeks went into giving him a life. Martin belonged to a club on Pall Mall. He bought his shirts from Gieves and smoked Player’s Navy Cut. His bank manager had written about an overdraft and his father had written to fret about the same overdraft, marking him a decent chap living slightly beyond his means.

He also had a fiancée. Pam existed as a photograph of a young woman from the naval intelligence office, two rather gushing love letters, and a bill for an engagement ring. The Imperial War Museums, which holds Montagu’s papers, lists the pocket clutter plainly enough: the ring receipt, a theatre ticket stub, the small paperwork that gives a man a personality.

Real cargo went into the briefcase. A private letter to General Sir Harold Alexander in North Africa hinted that the coming assaults would fall on Greece and Sardinia, with Sicily a feint. Lieutenant General Sir Archibald Nye drafted it himself so the tone would ring true. An eyelash was tucked into one of the folds. If the letter came back with the eyelash gone, somebody had opened it.

Huelva was picked with care: strong local currents, a pro-German fishing port, and a diligent Abwehr agent named Adolf Clauss who could be relied on to chase any rumour of a drowned British courier. Thirteen days before the drop, as the body was driven from London to a submarine base in Scotland, Montagu and Cholmondeley had to thaw Michael’s frozen feet with an electric fire to get his boots on, as reported in a later Times of Israel retelling.

What Berlin did with it

Spanish doctors put the death down to immersion in the sea, buried Martin with military honours, and let the Germans have an hour alone with the briefcase. Berlin’s assessment came back without a word of caution. Colonel Alexis von Roenne, the officer who signed it off, was privately an anti-Nazi with a habit of passing on intelligence he knew to be false.

The forgery cleared its final hurdle partly because a German colonel wanted it to.

Hitler ordered Greece, Sardinia and Corsica held at all costs. A Panzer division moved from France towards Thessaloniki. Torpedo boats left Sicily for the Greek islands, and by the end of June the garrison on Sardinia had doubled. Bletchley Park was reading the traffic throughout, and on 14 May London told Churchill the bait had been taken whole.

Sicily was invaded on 9 July. Four hours in, twenty-one German aircraft left the island to reinforce Sardinia. Planners had allowed three months for the campaign. It took thirty-eight days.

How much credit a dead man deserves

Historians have argued the arithmetic ever since. Michael Howard, writing the official history of British wartime intelligence, rated Mincemeat the most successful single deception of the war. Others note that Hitler was already convinced the Balkans were his soft flank and already distrusted his Italian allies, so the forged letters may have shoved a door that was ajar. One operation’s effect cannot be cleanly separated from everything else moving at once.

What happened to the man in the water is not in dispute. His name stayed classified for fifty years until a researcher turned it up in a declassified file, then went onto the headstone at Huelva in the late 1990s, as documented by Britannica. He had held down no job, left no family and gone unmissed in life. In death he was issued a club, a tailor, a girl who wrote him letters and an entire fictional war, and the Wehrmacht took him more seriously than anyone ever had.