Brief History from Wikipedia
The Sd.Kfz. 251 halftrack was a World War I German armored fighting vehicle designed by the Hanamag company, based on its earlier unarmored Sd. Kfz 11 vehicle. The Sd.Kfz. 251 was designed to transport the Panzergrenadier (German mechanized infantry) into battle. Sd.Kfz. 251s were the most widely produced German halftracks of the war, with at least 15,252 vehicles and variants produced by seven manufacturers. Some sources state that the Sd.Kfz. 251 was commonly referred to simply as "Hanomags" by both German and Allied soldiers after the manufacturer of the vehicle; this has been questioned, and may have been only a postwar label. German officers referred to them as SPW (Schützenpanzerwagen, or armored infantry vehicle) in their daily orders and memoirs.