The American M-209 cipher machine

There are several other good resources on the M-209.

Short cryptanalysis of M-209: http://www.jfbouch.fr/crypto/m209/cryptanalysis.html

Series on how to use the machine: https://www.nf6x.net/2013/03/practical-use-of-the-m-209-ciph...

Paper by James Reeds, Robert Morris and Dennis Ritchie analyzing its security from 1978: https://cryptome.org/2015/12/ReedsTheHagelinCipherBellLabs19...

Apparently the paper by Morris and Ritchie was not supposed to be published; it was instead a technical note. See Ritchie's account: https://www.bell-labs.com/usr/dmr/www/crypt.html