Notes
- Bamford , James . 1983 . The Puzzle Palace 13 388 London
- Beesly , Patrick . 1984 . Room 40 262 273 – 4 . 304 Oxford
- Andrew , Christopher . 1985 . Secret Service London Chapter 9.
- Denniston , A.G. 1986 . ‘The Government Code and Cypher School between the Wars’ . Intelligence and National Security , I ( 1 ) : 49