U.S. military planners experimented with half-track designs from the late 1920s and employed a number of vehicles during WWII. Among them was the M21 mortar carrier, which was officially adopted in June 1943. It featured a frame on the fighting compartment floor for the mortar that allowed sixty degrees of left and right traverse. The vehicle was also equipped with a 12.7mm heavy machine gun, bazooka, mines and a wide range of other weapons. It saw use until the 1960s as a training vehicle.