It is frequently said: there is no such thing as a friendly intelligence service, only an intelligence service of a friendly country. That was certainly the case with British intelligence and the United States in the early stages of the World War II.
As Britain fought alone, waiting for America to enter the conflict, Churchill instructed his intelligence chiefs to instigate a wide variety of influence operations on US soil to influence American public opinion and help pull the United States into the war. They were undertaken by a British intelligence outfit in New York, known under the deliberately bland title, British Security Coordination (BSC).
BSC’s activities involved smearing “isolationist” politicians and groups in the United States, like the “America First” movement. BSC operatives fabricated documents, which they then leaked to Roosevelt’s administration, including a map purporting to be Hitler’s plans for conquest in North and South America. Roosevelt used the map in one of his fire-side radio broadcasts as evidence of Hitler’s plans.
BSC also leaked pro-British stories to American newspapers. It secretly bankrolled an apparently independent radio station to disseminate British propaganda. BSC even recruited an agent, or spy, who worked for Gallup Poll in New York and betrayed some of its polling data. Doing so helped the British tailor their propaganda according to that polling. This has echoes with Russian meddling in the US presidential election seven decades later, in 2016. READ MORE from Calder Walton about British wartime meddling in the US.