All major nations developed self-propelled artillery that would be able to provide indirect support while keeping pace with advancing armoured formations. These were usually lightly armoured vehicles with an open-topped hull; the US M7 Priest, British Sexton (25 pdr) and German Wespe and Hummel being typical examples. A different route was chosen by the Soviets, who did not develop a specialized indirect fire vehicle, but following a tradition of dual-purpose towed artillery, built a series of versatile assault guns with indirect fire capabilities (example ISU-152). A related and novel program was the development of the Soviet Katyusha self-propelled multiple rocket launchers, which were unarmored trucks with a simple rocket rack on the back, a cheap and crushingly effective weapon, provided area saturation was called for rather than accurate fire.