American Codebreakers Made a Secret WWII Visit to Bletchley Park

Did you know that not all of the codebreakers at Britain’s Bletchely Park were British? In February 1941, America’s secretive 'Sinkov Mission' made a secret journey by ship across the Atlantic to exchange cryptanalytic information with Britain’s Bletchley Park.

"The Ys are coming!" Commander Alastair Denniston, then head of GCHQ's predecessor the Government Code & Cypher School, wrote in his diary. He was referring to the 'Yanks' arriving on the Top Secret Sinkov Mission.

Abraham Sinkov, the Philadelphia-born son of Russian immigrants, led the WWII team of American codebreakers who were disguised as 'Canadian diplomats' - a cover Sinkov thought no one would believe.

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American spies at Bletchley

The US team faced the challenge of gaining British trust amid inter-agency suspicions. Despite initial secrecy, the mission proved pivotal when the US shared the Purple cipher machine, ultimately leading to access to Bletchley's Bombe decryption machine. The success set the stage for future intelligence exchanges, strengthening the enduring US-UK alliance in codebreaking, later formalized in the post-war 'Five Eyes' intelligence alliance.

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