Since the end of the Cold War in 1991 the U.S. Army has drastically reorganized and reduced its artillery force. At the end of the Cold War most artillery was conventional “tube” artillery. That meant towed 105mm, 155mm, 203mm howitzers and self-propelled 155mm howitzers. The MLRS, a 16 tube 227mm unguided rockets was just entering service when the Cold War ended. In the 1990s it became obvious that smart bombs (JDAM) first used in the 1991 Gulf War, were more effective than artillery and that led to a major shift away from using artillery. By 2004 over 40 tube artillery battalions had been disbanded.
Another major change in 2004 was the introduction of the GMLRS (GPS guided MLRS) rocket. Like the unguided version, the GMLRS are packaged and used in containers (pods) holding six rockets each. Since then over 2,000 GMLRS rockets have been fired in combat. GMLRS rockets cost about $100,000 each and have been very successful. That has meant even less work for tube artillery, which had dominated the battlefield since the 17th century.
The 309 kg (680 pound) GMLRS (guided multiple launch rocket system) missile is a GPS guided 227mm rocket. It was designed to have a range of 70 kilometers and the ability to land within meters of its intended target, at any range. This is possible because it uses GPS (plus a back-up inertial guidance system) to find the target location it was programmed with. In 2008 the army tested GMLRS at max range (about 85 kilometers) and found that it worked fine. This enables one MLRS/HIMARS vehicle to provide support over a frontage of 170 kilometers, or, in places like Afghanistan, where the fighting can be anywhere, an area of over 20,000 square kilometers. This is a huge footprint for a single weapon (an individual MLRS/HIMARS vehicle), and fundamentally changes the way you deploy artillery in combat. By way of comparison, Excalibur (GPS guided 155mm shell) has a max range of 37 kilometers, and 120mm mortars about 7.5 kilometers.
Another reason for the success of the GMLRS has is the HIMARS rocket launcher. Only costing about $3 million each, these smaller, truck mounted MLRS (HIMARS) rocket launcher systems have become very popular. HIMARS carries only one, six MLRS rocket, container (instead of two in the original MLRS vehicle). But the 12 ton truck can fit into a C-130 transport (unlike the 22 ton tracked MLRS) and is much cheaper to operate. The first HIMARS entered service in 2005, about a year after GPS guided rockets did.
Most of the GMLRS rockets are fitted with an 89 kg (196 pound) high explosive ("unitary") warhead. About half of that is actual explosives. That's twice as much explosives as the air force 130 kg (285 pound) SDB (Small Diameter Bomb). A 155mm artillery shell has 6.6 kg of explosives, and the 500 pound (227 kg) bomb has 127 kg of explosives, which produced an excessive blast for many urban combat situations. The GMLRS seemed to be just right most of the time. In 2011 a GPS guided 120mm mortar shell entered service. This shell has about 2.2 kg (five pounds) of explosives in it and has become popular for situations when you want pinpoint accuracy in areas with nearby civilians.
GMLRS has been used with great success in Iraq and Afghanistan, where most have been fired so far. The guided rocket is much more effective than the older, unguided, version, and is replacing it in most cases. No more of the unguided rockets are being purchased by the U.S. The accuracy of GMLRS means that one rocket does the job that previously required a dozen or more of the unguided ones. That's why HIMARS is so popular. While HIMARS only carries six rockets, that's often enough to last for days, even when there's a lot of combat.
Noting the success of GMLRS, Russia and China have developed and put into service their own GPS guided rockets. Russia has long led in the design of new rocket systems was is playing catchup when it comes to using guided rockets. The multiple rocket launcher was first developed by the Russians before World War II as a cheap alternative to massed artillery fire by individual guns. Long seen as a supplement to regular artillery, the introduction of the high tech U.S. MLRS rocket system in the 1980s began to make a lot of conventional artillery obsolete even before GMLRS came along. Of course, artillery has always been ripe for innovation. The U.S. 175mm gun, introduced in the 1960s, was rendered obsolete in the 1980s with the introduction of special long range ammo for the 203mm (8 inch) howitzer. The U.S. Army stopped using the 175mm gun in the 1970s. When the MLRS entered service, one of the three batteries in each division's 203mm howitzer battalion was equipped with MLRS units instead. But MLRS proved so effective that the 203mm howitzer battalion became an MLRS battalion and the 203mm gun was dropped by the U.S. Army.
There were always non-divisional MLRS battalions, as the MLRS was seen, from the beginning, as an ideal weapon for massed artillery fire. The Gulf War allowed the MLRS to show off what a potent weapon it could be. The larger rockets also provided room for more complex payloads (cluster and "smart" munitions) and guidance systems. This was another example of how technology can transform an old weapon. While the Russians have been using rocket launchers for over 70 years, they never got around to enhancing their effectiveness with a lot of technology until recently and then only because they noted others were doing so and succeeding.