There were two main types of self-propelled guns in the German Army during WW2. One was fitted with an anti-tank gun and the other with an artillery howitzer, like the 15cm sFH 13/1 (Sf) auf Geschützwagen Lorraine Schlepper(f) Sd.Kfz.135/1. The vehicle fitted with the artillery howitzer was called a ‘Geschützwagen’, which is literally translated as a ‘gun vehicle’. The letters ‘SF’ stand for ‘Selbstfahrlafette’ – self-propelled carriage. The letter (f) indicates that the chassis was of French origin.