The Leica III DRP is a rangefinder camera introduced by Leica in 1933 and produced in parallel with the Leica II series. Several models were produced over the years, with significant improvements.
The Leica III uses a coupled rangefinder distinct from the viewfinder. The viewfinder is set for a 50mm lens; the lenses are screw mount vs the M-mount series of Leicas.
Serial No: 414578 IIIC from 1946
Here's a video on how to load the Leica III: