John R.F. Jeffreys

Jeffreys was educated at Brentwood School, Essex, and Downing College, Cambridge, where he graduated as a Wrangler in Part II of the mathematics tripos in 1936.

[6] Jeffreys was put in charge of a small section manufacturing perforated sheets for use in the cryptanalysis of the Enigma, a task which took over three months, completed on 7 January 1940.

[7] Jeffreys's perforated sheets were used by Polish cryptologists in exile in France to make the first wartime decryption of an Enigma message on 17 January 1940.

[8] In early 1940, a section called "Hut 6" — named after the building in which it was initially housed — was created to work on solving German Army and Air Force Enigma messages.

[9] Jeffreys was in charge of "Sheet-Stacking and Machine Room activities", while Welchman handled "Registration, Intercept Control, Decoding, and relations with the intelligence people in Hut 3".

A demonstration of Zygalski sheets , a tool for breaking the Enigma machine . This Polish invention was shared with the British in 1939, and the enormous task of manufacturing two complete sets of the sheets was supervised by Jeffreys.