Appendix 11

U. S. Army Cryptanalytic Bombe

The following description is from a 'Tentative TOP SECRET Memorandum for OP-20' dated 12 February 1945.1

'Subj: Op-20-G and S.S.A.2 Bombes, Comparison of.

1. In accordance with your request, the following comparison of the Op-20-G and the S.S.A. Bombes is submitted.

2. The Op-20-G Bombes were constructed at the U.S. Naval Computing Machine Laboratory. A total of 121 Bombes were assembled at a cost of about six million dollars. The mechanical portion of the unit consists of 16 Enigma equivalents consisting of a set of 4 spindles and brush holders on which cross-wired wheels are loaded by hand. Automatic electronic detection is supplied on each Bombe of such a nature that only correct 'stories' that satisfy all the restrictions of the 'menu' are printed. A three wheel run takes 50 seconds and a 4-wheel run takes 20 minutes. Each Bombe is 8 feet long, 7 feet high and 2 feet wide.

3. The S.S.A. Bombe was constructed by the Bell Laboratories at a cost of from one to one and one-half million dollars. It consists of a telephone exchange type of installation with a total of 144 relay equivalents of the Enigma and 12 control stations. Each Enigma equivalent is mounted on a rack approximately 7 feet long, 8 feet high and one-half foot wide. The 144 Enigma equivalents can be allocated in any desired manner to the control stations by plugboards. Wheel order changes are done by push buttons at the remote stations and can be changed in about 30 seconds. The other setup data must be placed individually on the Enigma banks on the floor. Normally, about 10 stations are running simultaneously and about 10 minutes is required for each station to run through a