A Banbury sheet, c. early 1940s. Used to break German naval Enigma messages in a process invented by Alan Turing, called…

cipherface:

A Banbury sheet, c. early 1940s. Used to break German naval Enigma messages in a process invented by Alan Turing, called Banburismus. The only surviving examples of these sheets were found inside the walls of Hut 6 at Bletchley Park in 2013.