Back to Zenit cameras. Particularly the early years. The original KMZ Zenit SLR was based on the company's Zorki camera line. The viewfinder and rangefinder were removed, and the mirror mechanism and pentamirror or pentaprism was added. This was pure Soviet innovation.
The prototype and pre-production/low production units were made from 1951 to 1953. Production in quantities began with the "regular logo" Zenit in 1953. Flash syncronization was added in 1955 resulting in the Zenit S model. Which puts the Soviet SLRs right up there with the Japanese on being near the birth of the 35mm SLR (Asahi in production in 1952 evolving into the Pentax in 1957). The Germans beat both with small production runs in the mid 1930s but WWII interrupted things.
This particular example was made in 1956. If one notices, I know exactly when the KMZ cameras were made. The reason is KMZ always started the serial number with the last two digits of the year it was made. Mind you that was not the year it was sold new necessarily. Being a state run industry, the factory did not have to pay attention to supply and demand. Some years the cameras just languished, other years, they would not ramp up production.
Below one can see its very much a Zorki. Uses the same M39 mount as the Zorki to reduce costs but with the Pentax/Asahiflex lens registration. Not sure why they choose that distance since Pentax used a M37 mount at the time. But the lens mount to film distance (lens registration) had to be increased to make room for the mirror anyway and it work out fine when both Pentax and KMZ went to M42 mounts.