We like to think that secret agents, coded messages and undercover saboteurs only belong in cheesy movies, but spies are very real. In fact, these 10 celebrities all lived a double life as spies during the Second World War:

1. Marlene Dietrich

The glamorous German actress burned up the screens in the '30s and '40s, but when the war broke out both America and Germany questioned her allegiance. Dietrich publicly condemned the Nazis, and did USO tours for troops overseas. But she was also investigated by the FBI, and had family living in Germany during the war.

The organization later enlisted her, giving the actress a chance to prove her dedication to America by "collecting observations about subversive activities in Europe" during her tours. To this day, historians debate whether Dietrich was an American spy or a double agent.

2. Roald Dahl

The children's book author was actually a Royal Air Force pilot at the start of the war, when a painful crash forced him to take a desk job instead. He moved to Washington, D.C., where he wrote British propaganda for American newspapers.

Eventually Dahl was given a much livelier job: seducing the wives and female relatives of American VIPs to learn their secrets. This included Congresswoman Clare Booth Luce, who was married to the publisher of Time magazine and so smitten with Dahl that he asked to be reassigned somewhere else.

3. Julia Child

Before her success as a celebrity chef, Child rose through the ranks of the Office of Strategic Services, which would later become the CIA. Starting out as a clerk, she was eventually promoted to a research position, developing shark repellent for underwater missions.

Later, Child was assigned to listening posts in far-off locations like China and Sri Lanka, where she recorded secret messages intercepted by the government.

4. Moe Berg

In the '20s and '30s, Berg was nicknamed "the brainiest man in baseball." Along with being a star player for the Dodgers, Berg was a Princeton grad who spoke 12 languages and earned four degrees, including a law degree from Columbia that he earned while playing ball.

When he was traded to the Washington Senators, Berg was recruited to spy for the U.S. government on his trips overseas. He recorded footage of Japanese military installations, and was once caught trying to sneak onto an air base.

Berg's most dangerous mission was a fact-finding trip to Germany, where he would identify if the Nazis were close to making a working A-bomb. If they were, Berg was told to shoot the project's head physicist Werner Heisenberg. Thankfully, he realized they were years away from building the weapon.

Keep reading to learn about more celebrity spies, including Cary Grant and Ol' Blue Eyes himself...

5. Cary Grant

The charming British actor had a long list of secrets, and one of the most shocking was his role as a spy during World War 2. The government feared German spies were burrowing into the entertainment industry, and recruited actors and producers to root them out.

The most surprising discovery of Grant's spy career involved another actor: Errol Flynn. Allegedly, Grant discovered that Flynn was a Nazi sympathizer, who personally sent letters to Hitler. It's too bad Grant turned down the role of James Bond, he would have been a shoe-in.

6. Lucky Luciano

The famous mobster and head of the Genovese crime family was facing a 30-50 year sentence when the Government approached him in 1942. They suspected a French troop ship had been destroyed by sabotage at an American dock, but the mob-affiliated workers wouldn't say anything.

Luciano convinced them to talk, helping to catch eight German spies in the process. He continued feeding the government information from his shipping sources, as well as tips for the upcoming Italian invasion from his connections in the country.

For his help, Luciano's prison sentence was reduced to just 10 years, but he was exiled to Italy after his release and spent the rest of his days there.

7. Greta Garbo

Garbo, a Swedish immigrant, found success in America during the '20s and '30s, but suddenly retired in 1941. Researchers strongly suspect that Garbo began working with the British MI6 after her "retirement," keeping tabs on important Swedes like indutrialist Alex Wenner-Gren.

She's even alleged to have helped smuggle a physicist from Cophenhagen to Berlin. That man was Niels Bohr, the scientist who helped America create the a-bomb.

8. Frank Sinatra

Yes, even Ol' Blue Eyes had a hand in the spy game. For years rumors had swirled that Sinatra was associating with mobsters, and some think his work with the CIA helped Sinatra get off the hook. The singer's daughter Tina claims that he helped transport smuggled documents and people using his private jet.

After all, what kind of security guard is going to hassle the Chairman of the Board at customs?

9. Ian Fleming

You might know this British writer as the creator of the 007 series, but he was a spy in his own right. Fleming spent most of World War 2 as a "middle man" for British naval intelligence, bridging the gap between top brass and spies working behind enemy lines.

He also helped draw an organizational plan for the OSS, which became the CIA, and headed up a special team called the 30 Assault Unit. These commandos raided enemy buildings ahead of the advancing army, stealing secret documents.

10. Christopher Lee

The Lord of the Rings actor's work during the war is so hush-hush that most of it is still classified. We do know that he worked for a top secret sabotage group called the Special Operations Executive, and another called the Ministry for Ungentlemanly Warfare. Lee is also believed to have hunted escaped Nazi officers once the war ended.

We'll let Lee explain his work in his own words:

"I was attached to the Special Air Service from time to time but we are forbidden "” former, present, or future "” to discuss any specific operations. Let's just say I was in Special Forces and leave it at that. People can read in to that what they like." Nuff said!

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