The U.S. Army is buying 46 more HIMARS rocket launchers, for about $3 million each. Because of the success of the GPS version of the U.S. MLRS rocket, the smaller, truck mounted MLRS (HIMARS) rocket launcher system has become more popular. HIMARS carriers 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.
The 680 pound GMLRS (guided multiple launch rocket system) missile is as GPS guided 227mm rocket that entered service six years ago. 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 its target. Two years ago, the army tested GMLRS at max range (about 85 kilometers) and found that it worked fine. This enables one 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 HIMARS vehicle), and fundamentally changes the way you deploy artillery in combat.
The U.S. Army is getting most of the 900 HIMARS vehicles ordered, with the marines getting the rest. There are also several export customers. The U.S. Army is buying 100,000 GMLRS rockets, most of them fitted with a 196 pound high explosive warhead. These have been used with great success in Iraq and Afghanistan, where over a thousand 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 it only carries six rockets, that's often enough to last for days, even when there's a lot of combat.