1. American Bombe. 1940. HCC NR 4361. This file contains a comprehensive set of photographs of the U.S. Army’s “Madam X” bombe, but the date shown for it in the NARA catalog entry is clearly too early.
2. ASA Memoranda on GEQ Crypt System. 1943. HCC NR 4318. See memo titled “System GEQ (Orange)—The Problem,” discussing potential SSA operations on this system.
3. Batey, J. K., M. L. Batey, M. A. Rock, and P. F. G. Twinn. 1945. GC&CS secret service Sigint volume II: Cryptographic systems and their solution. I Machine cyphers. TNA, HW 43/7. GC&CS.
4. Dilly Knox—A Reminiscence of this Pioneer Enigma Cryptanalyst