The U.S. Army has developed a new use for its M120A1 towed 120mm mortar. Rather than towing this Israeli-designed M120A1 lightweight mortar, the new version (called Sling system) will be carried in the back of a hummer, a light military truck. This is a variation of the many 155mm artillery systems that are mounted on the back of a heavy truck. The first of these was developed in the 1990s as the French truck-mounted 155mm Caesar. Entering service in 2003, France sent some Caesar howitzers to Afghanistan. The roads in Afghanistan are pretty bad and wheeled combat vehicles have a hard time of it, but Caesar was built to handle cross-country operations. When a Caesar vehicle halts, the four-man crew can extend the metal braces in the rear, raise the barrel, and be firing within minutes. After firing, the vehicle can be moving in less than a minute.
The Sling does not carry or fire the mortar from the vehicle, but it is quicker to unhook and emplace on the ground than the several minutes to ready the Caesar vehicle to fire. Sling can fire its first 16 13.7 kg (20 pound) shells one minute after its towing vehicle halts, and at ranges up to 7.8 kilometers. The Sling mortar is based on the Israeli Elbit K6 lightweight low-recoil mortar that weighs 146 kg (320 pounds).
The Sling was designed mainly for use by army Special Forces but can be useful for any infantry unit operating off-road and in need of mortar support for light infantry fighting at remote locations. That makes GPS guided shells more useful than unguided ones. Guided 120mm Sling shells weigh 17.3 kg (38 pounds) and have a range of 7.5 kilometers. They land within 10 meters (30 feet) of the aiming point. One guided shell will do the work faster and with one shell while unguided shells take longer and require more shells. Normally the first shot from an unguided 120mm mortar shell will land anywhere within a 136-meter circle. The shells that do not come that close, and some of those that do, often hurt nearby civilians, or even friendly troops. The GPS guided shell gets it right the first time. A guided mortar round is very useful in urban warfare, where a miss will often kill civilians. The 120mm mortar round has about 2.2 kg (five pounds) of explosives, compared to 6.6 kg (15) pounds in a 155mm shell. The smaller explosive charges limit collateral damage to civilians.
The GPS mortar round is deemed the most useful, especially since the troops are satisfied with that degree of accuracy in GPS-guided 155mm artillery shells, 227mm GMLRS rockets and JDAM bombs. These guided shells dramatically reduce the logistical problems that artillery and mortars encounter when they are in areas where getting supplies is difficult and dangerous. Opponents dread the use of guided shells because these hit targets without the normal use of several unguided shells fired to adjust the accuracy of the shells. A first-round hit means the troops in the target area have no opportunity to seek cover. Surprise is the key to success in combat be it with sniper fire or guided shells.