Hitler had always wanted to declare war on the US first rather than have Roosevelt beat him to it

“one of the great secret agents of the last war”, and described his martinis as “the most powerful” in America. They were so good, in fact, that Fleming was inspired by Stephenson’s recipe: “Booth’s gin, high and dry, easy on the vermouth, shaken not stirred”.

Stephenson’s wartime British operation infiltrated American pressure groups, hacked into the private communications of US congressmen and senators, subsidised and directed political protest groups, manipulated opinion polls, operated wiretaps, organised protests, and harassed political opponents. They also produced what was called at the time, as it is today, “fake news”, which they fed into the American news cycle.

By late 1941 this undercover British campaign had two distinct objectives: to change American public opinion about going to war; and to provoke Hitler into a declaration of DAY OF DESTINY: Hitler’s declaration of war and, clockwise from main picture, Stephenson with a radio invention, Roosevelt giving his fateful speech and the Mayflower Hotel war on the United States. The fake Nazi documents served both ends. They could further shift American public opinion towards war, and at the same time infuriate the Nazi hierarchy in Berlin.

Once Stephenson had approved the plan, the job of producing these fakes was passed on to his specialist forgery unit in Toronto, called Station M after the unlikely Briton he had put in charge.

This was Eric Maschwitz, the lyricist behind the hit song A Nightingale Sang In Berkeley Square, who was also a first-class forger. With Maschwitz’s help and guidance, a team of forgers in Station M had produced the two fake Nazi documents.

From Toronto they were couriered to the MI6 station in New York. From here it was up to Stephenson to get them on to Roosevelt’s desk in the White House. But how?

This was where “Wild Bill” Donovan came in. By then Stephenson and Donovan had an exceptionally close working relationship. Unknown to most Washington insiders, Stephenson was feeding a stream of British intelligence to Donovan, who would pass it on as US work.

Usually the first person to see Donovan’s latest batch of intelligence was the president himself.

So the two fake Nazi documents were passed to “Wild Bill”, who gave them to Roosevelt. But was the president in on the ruse? Almost certainly.

Based on everything we know today, including memoirs, diaries and a number of recently declassified documents, there is little doubt that the president knew these were British fakes. But he went ahead with the speech anyway.

What was the effect? Not only did it help push American public opinion towards going to war, it also caused a storm in Berlin. In the febrile days that followed, the state-controlled Nazi media launched a volley of denials and accusations at the White House. There was even a formal complaint.

This speech riled many Nazi officials, especially Hitler himself. Less than a fortnight later, when the German leader next spoke in public he could talk of little else. Indeed this made such a deep impression on the Nazi leader that it appears to have influenced what has since been described as his costliest mistake – his decision one month later to declare war on the United States.

After the Japanese attack on Pearl Harbor on December 7, 1941, Germany did not immediately declare war on the United States.

Hitler had no obligation to do so, and almost none of his senior military officers were calling for it. Germany remained at peace with the US until four days later, December 11, 1941, when the German leader surprised the world by declaring war.

IN A speech given on the same day, Hitler tried to justify his decision. He accused Roosevelt of “intolerable provocations”, “baseless allegations” and “shameless misrepresentations of truth”.We will never know exactly what he was referring to here. But it is highly possible the two British fakes played a part.

Hitler had always wanted to declare war on the United States first, rather than have Roosevelt beat him to it.

Until reading about the president’s speech, Hitler imagined Roosevelt to be incapable of persuading Congress to go to war against Germany. But what happened in the Mayflower Hotel changed all that.

Suddenly, it was as if he was up against a different type of opponent, one capable of lying to his people in order to take his country to war. From that moment, it was no longer a question of if Hitler would declare war on the US, but simply when.

Put another way, an MI6-led operation appears to have played a part in provoking Hitler into declaring war on America.

Churchill may have revealed too much, several months later, when he said America’s entry into the war was, “dreamed of, aimed at, and worked for, and now it has come to pass”.

Soon after Hitler’s declaration of war, Stephenson flew back to London. No doubt a few glasses were raised. We may never know. Already the details of this enormous operation began to be covered up.

But we do know that in 1945, at Churchill’s request, Stephenson, who survived the war and finally died aged 92 in 1989, was knighted. At the time, very few people could work out why.