The CD55 and CD-57 devices look identical from the exterior but the difference is very simple - it lies with the keying mechanism. The CD-55 works in the same way as the C-38, M-209 and C-446, and features simple stepping (so that could be broken easily by the NSA at the time). The CD-57 has a much more advance keying mechanism, based on the same principle as the C-52 and CX-52 (which was VERY difficult to break).
Development of both machines was started in 1955 and was completed
in 1957. Both machines appeared on the marked in 1957. The differences
were never explained to potential customers. NATO and NATO-friendly countries
were allowed to buy the CD-57. Other countries (in particular the Arab
countries) were only offered the CD-55. One of the most prominent customers
of the CD-55 machine was the Vatican.
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| Top view with rotors |
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| Side view with rotors |
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| The rotors themselves |
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| Without rotors. |
| All photos in this table by Gerhard Sulger-Buel |