The Sonderkraftfahrzeug (Sd. Kfz.) 251 half-track had its origins in the same requirement as the smaller and lighter Sd. Kfz. 250. Intended as an armored personnel carrier, the Sd. Kfz. 251 entered service in 1939, and quickly became the standard means of transport for the panzergrenadiers. As it turned out, the Sd. Kfz. 251 was an especially useful vehicle, not only capable of keeping up with the newly formed panzer divisions but also providing invaluable support as well. All told, there were 22 special-purpose variants built, including the menacing-looking Stukavoss ("infantry Stuka"), which mounted a series of rocket launchers on the outer sides of the vehicle. Other variants included a flame-thrower, anti-tank, and communications vehicle, as well as an observation post, ambulance, and infra-red searchlight carrier. Despite suffering from early reliability problems, the Sd. Kfz. 251 was produced by the thousands, eventually becoming a trademark of the German panzertruppe on all fronts.