1939 Leica IIIb (G - 1938) is similar to the IIIa except the viewfinder / rangefinder windows are placed immediately next to each other and the diopter adjustment is now a lever under the rewind knob. This is the last pre-war Leica.  This example has the super fast post-war Summarit f1.5 / 50mm lens which was the successor to the pre-war Xenon of similar design.