The most widely produced German half-track, Sd. Kfz. 251 was introduced in 1939 and remained in production throughout the war, with at least 15,252 units produced. The popular Hanomag, as it was called by both Allied and Axis soldiers, was distinguished by its heavily angled armored hull and a very large track area with no return rollers, providing good traction and performance. The use of Schachtellaufwerk, overlapping and interleaved road wheels, contributed to it, at the cost of increased maintenance and severe vulnerability to Soviet winters and mud seasons, where they could be frozen solid.