new position. This ability is very useful in a mobile conflict and particularly on the advance. Conversely, towed artillery was and remains cheaper to build and maintain. It is also lighter and can be taken to places that self-propelled guns cannot reach, so despite the advantages of the self-propelled artillery, towed guns remain in the arsenals of many modern armies. Assault gun An assault gun is a gun or howitzer mounted on a motor vehicle or armoured chassis, designed for use in the direct fire role in support of infantry when attacking other infantry or fortified positions. Historically, the custom-built fully armoured assault guns usually mounted the gun or howitzer in a fully enclosed casemate on a tank chassis. The use of a casemate instead of a gun turret limited these weapons' field of fire, but allowed a larger gun to be fitted relative to the chassis, more armour to be fitted for the same weight, and provided a cheaper construction. In most cases, these turretless vehicles also presented a lower profile as a target for the enemy. Self-propelled siege mortar A Siege mortar is a form of self-propelled gun that holds a siege mortar. The only siege mortar ever built was the Karl-Gerät. It could be argued that these could be classified as a Mortar carrier . Mortar carrier A mortar carrier is a self-propelled artillery vehicle carrying a mortar as its primary weapon. Mortar carriers cannot be fired while on the move and some must be dismounted to fire. In U.S. Army doctrine, mortar carriers provide close and immediate indirect fire support for maneuver units while allowing for rapid displacement and quick reaction to the tactical situation. The ability to relocate not only allows fire support to be provided where it is needed faster, but also allows these units to avoid counter-battery fire. Mortar carriers have traditionally avoided direct contact with the enemy. Many units report never using secondary weapons in combat. Prior to the Iraq War, American 120 mm mortar platoons reorganized from six M1064 mortar carriers and two M577 fire direction centres (FDC) to four M1064 and one FDC. The urban environment of Iraq made it difficult to utilize mortars. New technologies such as mortar ballistic computers and communication equipment and are being integrated. Modern era combat is becoming more reliant on direct fire support from mortar carrier machine guns. Multiple rocket launcher A multiple rocket