May 6, 2022 1:44 PM EDT

Operation Mincemeat—a historical drama chronicling an audacious World War II plot by the British intelligence services to dupe the Nazis—drops on Netflix May 11. Starring Colin Firth and Succession’s Matthew Macfadyen, the movie dramatizes a mission that played a crucial role in turning the tide in the Allied forces’ favor in the war’s later years.

What may come as a surprise to many viewers is that despite its far-fetched plot—which features a corpse with a fake identity, a briefcase stuffed with false documents, and James Bond creator Ian Fleming—the movie is largely faithful to the real historical events. Here’s the true story behind Operation Mincemeat.

What was Operation Mincemeat?

In 1943, Allied forces comprising Britain, France, Canada, the U.S., and Australia planned to launch an offensive on the Italian island, Sicily, to topple Benito Mussolini’s fascist regime, which supported the Nazis in the war.

To ensure the success of the invasion, two British intelligence officers came up with an elaborate plan to deceive the Nazis and draw their allied armies away from the Italian coast. Charles Cholmondeley (Matthew Macfadyen) and Captain Ewen Montagu (Colin Firth) decided to plant a dead body disguised as a member of the British royal marines off the coast of Spain. At the time, Spain was ruled by the dictator Francisco Franco, and although it was officially neutral in the war, the country shared intelligence with the Nazis. The corpse had a briefcase stuffed with what appeared to be top secret documents suggesting that the Allies next target would be Greece—which had been occupied by the Italians and Nazis since 1941—and a different Italian island, Sardinia.

But the dead marine, called Major William Martin, and the documents he held were entirely fabricated. The corpse was in fact Glyndwr Michael, a 34-year-old man who had become homeless after moving to London from Wales and died after ingesting rat poison. With the help of a London coroner, Cholmondeley and Montagu chose Michael as he had no known relatives looking for him—his identity wasn’t revealed publicly until the 1990s.

The briefcase also contained a photograph of Major Martin’s supposed fiancée, a receipt for an engagement ring, and a theater ticket stub—all planted to suggest authenticity. When the Spanish found the supposedly drowned marine, the British authorities scrambled to retrieve the briefcase he was found with to convince the Nazis of the enclosed documents’ validity.

Matthew Macfadyen and Colin Firth in 'Operation Mincemeat'
Giles Keyte/Courtesy See-Saw Films and Netflix, and Haversack Films Limited

Did Operation Mincemeat work?

The Nazis recovered the briefcase from the Spanish, and a copy of the fake documents reportedly went straight to Adolf Hitler himself. Fearful of the Allies’ supposed plan to take back Greece, he redirected Nazi troops to defend the territory. As a result of the false information, the Nazis were caught off guard when, in July 1943, 160,000 Allied troops invaded Sicily and took control of the island in just over a month. The British leader reportedly received a telegram informing him of the operation’s success, saying: “Mincemeat swallowed rod, line and sinker.”

The successful invasion was considered a turning point in the war, accelerating Mussolini’s downfall later that month and supporting the Allies in their eventual victory in Europe in September 1945.

What were the roles of Colin Firth and Matthew Macfadyen’s characters?

Cholmondeley (pronounced “Chumley”), played by Macfadyen, was an eccentric secondee to the intelligence unit from the Royal Air Force, despite having reportedly never flown. Montagu, played by Firth, had been a lawyer before signing up with naval intelligence during the war. Together, they led a team known as Section 17M based in a basement room of the British naval headquarters in London.

Cholmondeley and Montagu had worked for the secret XX Committee in the British secret service, where they were regularly confronted with double agents, counter-espionage, counter-intelligence, and misinformation.

Montagu and Cholmondeley both received military awards for their role in the operation.

What parts of the movie are made up?

In the movie, suspicions fall on Montagu as the British intelligence service believe that his brother Ivor, played by Mark Gatiss, is a Russian spy. Cholmondeley is enlisted to spy on Montagu during the operation to assess the threat his brother may pose.

In reality, Montagu’s brother Ivor was a committed communist and had once worked for the Russian secret service. While the British were suspicious of him and even tapped his phone, his impact on the operation was thought to be limited. There’s also no evidence to suggest that Cholmondeley was spying on his colleague.

Another embellished subplot of the movie is a love triangle between Cholmondeley, Montagu, and Jean Lesley, played by Kelly Macdonald. Lesley worked as a secretary for the British secret service, and her photograph was planted in the briefcase as the “fiancée” of the fabricated marine. Although Lesley knew the two men, there’s no evidence that they were vying for her affections.

For more of TIME’s culture coverage, subscribe to our entertainment newsletter, More to the Story, by clicking here.

How was James Bond author Ian Fleming involved?

The movie is narrated by Ian Fleming (Johnny Flynn), the James Bond author who worked for the British naval intelligence division during the war.

Around the time of Operation Mincemeat, Fleming was assistant to Admiral Godfrey, the head of naval intelligence. Fleming suggested the corpse plot to Godfrey as a clever way to trick the Nazis after reading a similar storyline in a novel. Cholmondeley and Montagu ran with the idea, expanding it to the fantastical scale depicted in the movie.

Inspired by his time in the intelligence unit, Fleming later went on to write 14 novels revolving around the fictional spy, James Bond. It’s been suggested that Admiral Godfrey was Fleming’s basis for Bond’s boss, “M”, while another agent involved in Operation Mincemeat, Charles Fraser-Smith, inspired Bond’s gadget-making colleague, “Q.” Fraser-Smith designed a special container to preserve the fake marine’s corpse during its time in the water, which was then released into the sea from a British submarine.

More Must-Read Stories From TIME

Contact us at letters@time.com.

Read More From TIME
You May Also Like
EDIT POST