starting with the SU-85, and by late 1944 the SU-100, which mounted powerful guns on modern chassis adopting the full-casemate enclosure of the crew compartment as the Germans had done with the StuG III. These had the advantage of being relatively cheap to build and mounting a larger gun compared to the conventional tank that they were derived from, but at the expense of flexibility. Heavily armoured assault guns were designed to provide direct-fire support to infantry in the face of enemy defenses. Although often similar to tank destroyers, they carried larger caliber guns with weaker anti-armor performance but capable of firing powerful HE projectiles. The German 105mm howitzer-armed StuH 42 based on the StuG III, and the immense 152mm howitzer-armed, Soviet ISU-152, both fully casemated in their design, are examples of this type of self-propelled artillery. 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. The Axis powers had captured the Katyusha and made their own versions; Germany created the 8 cm Raketen-Vielfachwerfer, while Romania developed the Mareșal tank destroyer, an early prototype of which was armed with a Katyusha. It also had self-propelled howitzer versions. After the end of World War II, the assault gun fell from use with a general trend towards a single heavy gun-equipped vehicle, the main battle tank, although some wheeled AFV's such as the South African Rooikat, the Maneuver Combat Vehicle of the JGSDF, and the US M1128 MGS, among others, are still developed with large-caliber, direct fire weapons. Self-propelled indirect-fire artillery remains important and continues to develop alongside the general purpose field gun. Mortars Many vehicles have used ancillary smoke mortars for local defense, which project one or more smoke grenades in