Stencil Subtractor

The Stencil Subtractor frame was a ciphered text recyphering tool that was invented by British Army Intelligence Officer and cryptographer John Tiltman and was ready for trial by April 1941 but was not adopted officially by the British Forces until March 1942, and not brought into service until June 1943. It replaced the venerable and vulnerable Subtractor tables which had been previously used to encipher British military (Military communications) and civilian codes during World War II.