There are several other good resources on the M-209.<p>Short cryptanalysis of M-209: <a href="http://www.jfbouch.fr/crypto/m209/cryptanalysis.html" rel="nofollow">http://www.jfbouch.fr/crypto/m209/cryptanalysis.html</a><p>Series on how to use the machine: <a href="https://www.nf6x.net/2013/03/practical-use-of-the-m-209-cipher-machine-chapter-1/" rel="nofollow">https://www.nf6x.net/2013/03/practical-use-of-the-m-209-ciph...</a><p>Paper by James Reeds, Robert Morris and Dennis Ritchie analyzing its security from 1978: <a href="https://cryptome.org/2015/12/ReedsTheHagelinCipherBellLabs1978.pdf" rel="nofollow">https://cryptome.org/2015/12/ReedsTheHagelinCipherBellLabs19...</a><p>Apparently the paper by Morris and Ritchie was not supposed to be published; it was instead a technical note. See Ritchie's account: <a href="https://www.bell-labs.com/usr/dmr/www/crypt.html" rel="nofollow">https://www.bell-labs.com/usr/dmr/www/crypt.html</a>