The Sigsaly Telephone

Cabinet War Rooms, London SW1

Museum and gallery staff put their favourite artefacts on display

This curiosity, a telephone without dial or buttons, was the deceptively simple piece of apparatus behind the most advanced scrambler of the Second World War.

Code-named “Sigsaly”, this device enabled Winston Churchill and President Roosevelt to talk to each other across the Atlantic without fear of being overheard. Developed by the Bell Telephone company in the USA, the system was shipped to Britain in 1943.

This telephone and an intermediate scrambler were installed in the Cabinet War Rooms, Churchill’s underground headquarters in Whitehall, but the bulk of the scrambling equipment was housed in a basement annexe of Selfridges department store in Oxford Street. The reason? The equipment consisted of over 850 separate items and there was simply no room for it in the Cabinet War Rooms.

As it was, the Sigsaly found itself shoe-horned into a rather small cupboard formerly used for storing cleaning materials. In this most spartan of conditions Churchill was able to chat to Roosevelt, and later Truman, in complete secrecy. However, Churchill had a habit of ringing them on impulse, without taking account of the time difference between the two countries. So, in an effort to curb the number of times the presidential slumbers were interrupted, a clock was installed with two sets of hands, showing both British and American time.

Few people knew what this little room was really used for. Knowledge was restricted on a strictly need-to-know basis. One popular explanation was that it was the only proper loo in the building (there being only chemical toilets within the complex), and was reserved, naturally, for the Prime Minister’s exclusive use.

Until the Sigsaly’s installation, all transatlantic telephone calls had taken place over an ordinary commercial line. Censors would listen in, brief the callers on maintaining vigilance in case of enemy interception, and cut people off should they be indiscreet. There was even a censor for all the calls of the Cabinet and Prime Minster - a young woman of 22, whose reminiscences are held on tape at the War Rooms and who appears to be completely unaware that the really serious conversations were going on beyond her reach on an entirely different line.

Samantha Heywood is the education officer at the Cabinet War Rooms, Clive Steps, King Charles Street, London SW1. Tel 0171 930 6961