It was competitor to the Nikon F, came out in 1966, interchangeable viewfinders, screen, had motor drive, what DM stood for. Has a winder as well, and a bulk film back. Meter is built in, when using waist level finder still have meter access. The mount is Exkta which is why the shutter release is in the front rather than on top. Swiss Alpa, early Miranda and Petri also had front shutter release. The RE version was at the same price class the Nikkormate. The DM was the U.S Navy's 35mm until Topcon left the camera business in late 70s.