Enigma: the Dropping of the Double Encipherment. - Gilbert Bloch; Ralph Erskine (Cryptologia, 1986)

Enigma before Ultra Polish Work and the French Contribution. - Gilbert Bloch; Cipher A. Deavours (Cryptologia, 1987)

Enigma Before Ultra - the Polish Success and Check (1933-1939). - Gilbert Bloch; Cipher A. Deavours (Cryptologia, 1987)

Enigma Avant ultra Enigma before ultra. - Gilbert Bloch; Cipher A. Deavours (Cryptologia, 1988)