Of the many variables that take place during any conflict, supply and mobility are the most pressing. Germany realized this fact very early in World War 2 and demonstrated use of support vehicles during their early "Blitzkriegs". They had developed a great number of vehicles for differing purposes and a very successful on was the Sd.Kfz. 251 half-track. This semi-tracked vehicle became the centerpiece of their mechanized corps throughout the conflict. Production began in 1939 and the series is broken down into four types, from Ausf.A to D. according to the differences in design and its production period. Early models used a very complicated hull construction, made up of obliquely placed armor plating. This was somewhat simplified in the C and D types, to make mass production easier.