The M209 cipher machine: a war of words

The author describes the construction and operation of the M209 cipher machine as used by the US Army in the Second World War. It was one of several versions of the Hagelin machine, named after its inventor, Boris Hagelin, which was produced in Sweden. The author discusses the internal configuration, encipherment, overlapping, security, and cracking the code. The M209 remained in use until the mid-1970s when digital computers replaced them