Ausf.A & Ausf.B - produced in small numbers from 1939. Ausf. A and B models can be identified by the structure of the nose armor, which comprised two trapezoidal armor panels - the lower of which had an engine cooling vent. The B model, which began production in 1940, eliminated the fighting compartment's side vision slits.
Ausf.C - started production in mid-1942, featured a simplified hexagonal-shaped forward armored plate for the engine. Models A through C had rear doors that bulged out. The C model had a large production run, but was quite complex to build, involving many angled plates.
Ausf.D - started production in early 1943, was developed with the purpose of halving the number of angled body plates, simplifying the design and thus speeding up the production. D models can be easily recognized by their single piece sloping rear, with flat doors.
Sd.Kfz.251/7 - Pionierpanzerwagen (assault engineer vehicle), to carry assault bridge ramps on the sides.