In June of 1941, Americans read about an extraordinary British mission into Nazi-occupied France. Newspapers, including the Baltimore Sun and New York Post, detailed how the British parachuted into an airfield with tommy guns and hand grenades, overpowered the guards and destroyed about 30 planes. All of the team members made it back to Britain alive via torpedo boats, along with 40 German prisoners in tow. It was an incredible story.

It was also completely made-up.

Unbeknownst to the United States, the British foreign intelligence service known as MI6 had planted the story in the press as part of a covert influence campaign to convince the country to enter World War II. With Hitler aggressively gaining ground across the continent and dropping bombs over London, British Prime Minister Winston Churchill had been anxiously lobbying Franklin D. Roosevelt for reinforcements against the Germans, but America firmly resisted being drawn into another bloody war on the European continent. In May 1940, after the Nazis invaded the Low Countries and France, a Gallup poll reported that only 7% of Americans thought the U.S. should declare war on Germany. In April 1941, the aviation hero Charles Lindbergh and the America First Committee led a massively popular campaign against U.S. entry into WWII, a conflict many Americans didn鈥檛 see as winnable.

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鈥淎mericans generally did not see Britain as some close, beloved ally at the start of the Second World War,鈥 says Henry Hemming, author of . 鈥淏ritain was instead one of the major economic rivals to the United States.鈥 In addition, the colonialist British Empire, which America had proudly detached itself from, 鈥渨as hugely unpopular, and understandably so.鈥

By November 1941, though, polls suggested that a majority of Americans now favored entering the war to help defeat Germany. Why the shift? Earlier that year, according to Hemming鈥檚 book,, a decorated WWI fighter pilot and source of inspiration for James Bond (Ian Fleming noted Stephenson鈥檚 martinis were 鈥渟haken, not stirred鈥), was installed as the head of MI6鈥檚 U.S. office. A personal friend of Churchill, Stephenson (code name: 鈥淚ntrepid鈥) began to employ new tactics to sway public opinion about the war鈥攁nd convince the U.S. to come off the sidelines.

READ MORE: 10 Things You May Not Know About Winston Churchill

The British worked to seed U.S. intelligence

Bettmann Archive/Getty Images
General William J. Donovan, wartime OSS chief, presenting the medal for merit to Canadian-born Sir William S. Stephenson, who was director of British Security Coordination in the Western hemisphere from 1940-45, circa 1946.

鈥淭here are three major strands to what he does,鈥 Hemming says. One was to persuade the U.S. to establish its first intelligence office and convince William 鈥淲ild Bill鈥 Donovan to run it. Both of these events unfolded in July 1941, when President Roosevelt created a new intelligence organization called the Office of the Coordinator of Information, or COI (a predecessor to the CIA), and appointed Donovan鈥攚hom Stephenson had been courting as a sympathetic ally鈥攖o lead it.

鈥淢ost of the material that [the COI is] passing on to the White House鈥riginates with MI6 and British sources, and that givens Stephenson enormous power in terms of what American government officials are reading about the stakes of the war,鈥 he says. 鈥淭hat plays a significant and sometimes overlooked part in helping to precipitate this shift towards the idea that the British are doing alright, that the war in winnable, that Nazi Germany should be taken on.鈥

READ MORE: World War II's 'Most Dangerous' Allied Spy Was a Woman with a Wooden Leg

MI6 quietly bolstered anti-isolationist groups

Another part of the covert campaign involved infiltrating U.S. pressure groups that were already trying to get the U.S. to enter the war. MI6 operatives influenced these organizations鈥 campaign strategies and made sure they had adequate funding.

In April 1941, MI6 operatives helped organize a protest of an America First rally in New York City. When a female protester approached the mostly male ralliers that day, one of the men charged at her and punched her in the face, sparking violent clashes between the groups, Hemming writes. MI6 operatives used the media attention to promote their messages about the war.

鈥淩eports in the next day鈥檚 papers focused on the violence, with most articles also listing the different interventionist groups involved in the march and what their spokespeople had to say about Lindbergh and America First,鈥 Hemming writes in his book. 鈥淎nyone reading these with a keen eye might have noticed that some of the activists used very similar language. It was almost as if they were reading from the same script: which, as it happened, some of them were.鈥

READ MORE: FDR, Churchill and Stalin: Inside Their Uneasy WWII Alliance

The South American map and other 鈥榝ake news鈥

Adolf Hitler, WWII
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Adolf Hitler with General Wilhelm Keitel (left) and General Walther von Brauchitsch viewing a map, circa 1941.

The third part of the campaign involved setting up an office for MI6 operatives to distribute fake news. These were stories like the one about the bogus British raid meant to convince the public that the war against Germany was winnable and the U.S. should join Britain in the fight.

At its peak, the office planted more than 20 stories a week. For one, Stephenson鈥檚 office drew a fake map purporting to show Adolf Hitler鈥檚 plans to invade South America, and made sure this map ended up on FDR鈥檚 desk at the White House.

It did. In October 1941, FDR declaring that the map 鈥渕akes clear the Nazi design not only against South America but against the United States as well.鈥

鈥淲hen Hitler hears about this, he鈥檚 furious, he鈥檚 outraged, because he knows that this map is a fake,鈥 Hemming says. 鈥淎nd when Hitler gives his next public speech, he can talk of almost nothing but this particular map.鈥

READ MORE: How South America Became a Nazi Haven

The map, Hemming argues, not only influenced America鈥檚 decision to go to war against Germany. It also influenced Hitler鈥檚 decision to declare war on the United States on December 11, four days after the Japanese attack on Pearl Harbor. This was something Germany had no obligation to do after the U.S. declared war on Japan.

A few hours after declaring war on the United States, Hitler explained his reasons for doing so in the Reichstag, Nazi Germany鈥檚 pseudo-parliament. 鈥淎 lot of the reasons are about Roosevelt,鈥 Hemming says.

鈥淔irst he incites war, then falsifies the causes,鈥 Hitler declared on December 11, 1941. 鈥淭hen odiously wraps himself in a cloak of Christian hypocrisy and slowly but surely leads mankind to war.鈥

Both the United States and Hitler鈥檚 Germany were now primed for the fight.