"Operation Mincemeat," which is now available on Netflix, showcases one of the biggest stunts the British army pulled during World War II. In the film, Colin Firth dresses up as a corpse to fool the Germans. 

Here’s what really happened. 

In 1943, Ewen Montagu, who is played by Firth, and the British military misdirected the German military away from the Invasion of Sicily with a dead body for the German forces to find. On the dead body were documents for the Nazis to find, which suggested there was an invasion of Greece and Sardinia. 

Colin Firth attends the "Operation Mincemeat" UK premiere at The Curzon Mayfair on April 12, 2022 in London, England.

Colin Firth attends the "Operation Mincemeat" UK premiere at The Curzon Mayfair on April 12, 2022 in London, England. (Photo by Gareth Cattermole/Getty Images for Warner Bros)

Two British officers carried out this plan, Montagu and Charles Cholmondeley, who is played by Matthew Macfadyen. The two men obtained the body of a dead, homeless man and gave him a new identity, Captain William Martin. The homeless man had died of rat poisoning.

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The British army then released the body on the Southern coast of Spain, and it was discovered by fisherman. Before the men on the sea returned the body and documents to the British, they notified the Germans.

Later, decryptions of German messages proved that the British military’s plan worked. German forces went to Greece instead of Sicily, which led to a successful invasion.

Author Ben Macintyre wrote "Operation Mincemeat: The True Spy Story that Changed the Course of World War II," which the Netflix film is based on. Macintyre has been outspoken in the past about how this movie is a depiction of what really happened in World War II. 

(L-R) Thelma Adams, John Madden, Colin Firth, Michelle Ashford, and Thomas Newman speak onstage during Netflix's "Operation Mincemeat" special screening in Paris in May.

(L-R) Thelma Adams, John Madden, Colin Firth, Michelle Ashford, and Thomas Newman speak onstage during Netflix's "Operation Mincemeat" special screening in Paris in May. (Photo by Theo Wargo/Getty Images for Netflix)

"It wasn’t until MI5 began declassifying its files that you could really begin to tell true stories about a subject that’s been so heavily mystified and fictionalized," he said in the press notes interview. 

"And so I began to look into the MI5 files, and they really are the most extraordinary cornucopia of detail because they’re written by and for people who never expected them to be made public. They were always intended to be kept secret. And so they’re honest in a way that most official files are not. Most people who know that this material is going to come out one day try to shade it slightly. They try to slightly cover up or make themselves look better or other people look worse. Not in these files. They’re absolutely genuine accounts of what is going on."

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The homeless man who received a new identity is who some believe was Glyndwr Michael. It was never officially confirmed who the dead body was, and Montagu refused to identify the person his own book, "The Man Who Never Was: The Remarkable Story of Operation Mincemeat." 

Kelly Macdonald attends the UK Premiere of  "Operation Mincemeat" at The Curzon Mayfair in April.

Kelly Macdonald attends the UK Premiere of  "Operation Mincemeat" at The Curzon Mayfair in April. (Photo by Mike Marsland/WireImage)

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Alongside Firth, the Netflix film stars Kelly Macdonald, Lorne MacFadyen, Matthew Macfayden and Paul Ritter.