1. Carter, F. 2008. The first breaking of Enigma: Some of the pioneering techniques developed by the Polish Cipher Bureau. The Bletchley Park Trust Reports, New Edition, Report Number 2.
2. Carter, F. 1999. The first breaking of Enigma: Some of the pioneering techniques developed by the Polish Cipher Bureau. The Bletchley Park Trust Reports, Report Number 10.
3. Rejewski's Catalog
4. RECOVERING THE WIRING OF ENIGMA'S UMKEHRWALZE A