In February 1941 four US officers were landed from a British warship at Sheerness, bundled into vehicles and driven to Bletchley Park, Buckinghamshire, a large redbrick house amid wartime huts. They were greeted at midnight by the head of Bletchley with sherry, whisky being in short supply.

They carried with them a secret device called the Purple Machine, which deciphered previously impregnable Japanese communications.