a pattern that allows them to lay down a smoke screen some distance in order to conceal the vehicle from enemy observers. Mortar carriers are vehicles which carry a mortar as a primary weapon. Numerous vehicles have been used to mount mortars, from improvised civilian trucks used by insurgents, to modified IFV's, such as variants of the M3 half track and M113 APC, to vehicles specifically intended to carry a mortar, such as the 2S31 Vena. The Israeli Makmat is a mortar carrier based on the M4 Sherman tank chassis. The Russian army uses a 2S4 Tyulpan (Tulip) self-propelled 240 mm heavy mortar. Patria Hägglunds, a joint venture between Finnish Patria and Swedish BAE Systems Hägglunds manufactures AMOS (Advanced Mortar System), which is a 120 mm automatic twin barrelled, breech loaded mortar turret. There are also numerous AFV's and even MBT's that can be equipped with a mortar, either outside or inside of the cabin. The Israeli Merkava MBT carried a 60mm mortar in the small troop compartment in the rear, which fired through an opening in the roof, allowing the crew to remain protected. This was useful for fighting nearby infantry, as a mortar is shorter ranged and cheaper to shoot than the large main gun, as well as being better suited to wounding enemy infantry taking cover behind objects. However, since the mortar is only a secondary weapon in this case, the Merkava is not considered a mortar carrier. Howitzers and guns Self-propelled artillery remains important in the equipment of many modern armies. It saw a significant role throughout the Cold War era conflicts and in the recent Gulf Wars. Modern SP artillery is highly computerized with the ability to self survey firing positions using systems such as GPS and inertial navigation systems. This, in conjunction with digital fire control/ballistic computers and digital communications, allows individual guns to disperse over a wide area and still deliver rounds on target simultaneously with the other guns in their battery. These capabilities also increase survivability manyfold as modern SP artillery can displace and avoid counterbattery fire much more quickly and effectively and, if desired, more frequently than previously possible. In conjunction with modern logistic systems (where the SP gun's systems can track and report on ammunition consumption and levels) with similar navigation systems and palletized load dropping/lifting capabilities mean that the rapid displacement can occur without significant disruption to actually firing