The U.S. Army used the M-209 encryption device during WWII starting in 1942. It's a compact unit (the outer housing is only 7 x 3.5 x 5.5 inches) and quite rugged. Operating the unit is straightforward.
If you have other information/stories about the M-209, or possibly used one yourself, please contact me by clicking the "contact" link on the navigation bar to the left.