THE SIEMENS CIPHER TELETYPE IN THE HISTORY OF TELECOMMUNICATIONS
Wolfgang W. Mache · Cryptologia · 1989
This paper spans a period from early pioneers in electrical telegraphy and telephony to the roots of the Geheimschreiber: the (electric) Siemens Schnelltelegraphy and the development of the first electrical teletypewriter “T25” by Wernerwerk 1, Berlin, in 1928. The paper expresses the opinion that the Geheimschreiber: T52d/e was not cracked by Bletchley Park's deciphering machines during WWII.