The U.S. Army has found that GPS guided shells were more successful, but less frequently used, than anticipated. So they reduced orders for these weapons, which entered service in 2007. The GPS guided 155mm Excalibur shells were used less frequently largely because other precision munitions often take out targets before Excalibur gets a chance to. There’s a growing number of other GPS (or laser) guided weapons available. The GPS guided MLRS (GMLRS) rocket has been especially popular. And the army uses a lot of laser guided Hellfire missiles, fired from AH-64 helicopter gunships. In addition to the reduction in Excalibur production, the army cut orders for GPS guided 120mm mortar shells (introduced in 2011) after a year of use.
Excalibur had other problems, mainly in the form of PGK (Projectile Guidance Kit) shells. PGK is actually a large fuze that screws into the front of a 155mm or 105mm shell. This longer fuze contains a GPS and small fins to guide the shell to a precision hit. It is less precise than Excalibur. That is, the PGK will ensure that the shell lands within 50 meters of the target. If it does not hit within 150 meters, PGK deactivates and the shell does not explode. An unguided shell will normally land within 250-300 meters of where it is aimed. An Excalibur shell lands within four meters of the target but costs more than twice as much as PGK. The army recently sent the first PGKs to Afghanistan, after successful testing in the United States. The big question is how important will the troops find the accuracy differences of Excalibur and PGK.
Another factor that hurt the popularity of Excalibur, and the 120mm guided mortar shell, is cost. Excalibur was supposed to cost about $50,000 each. Eventually, after all the debugging, and after more of the shells were produced. But the cost is still about $100,000 per shell. The 120mm GPS (using the same tech as PGK) guided shell is also pricey, but not as much as Excalibur. GMLRS cost about $100,000 each and have a much longer range and a bigger bang.
Another edge 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.
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 its target. In 2008, the army tested GMLRS at max range (about 85 kilometers) and found that it worked fine. This enabled 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. Excalibur has a max range of 37 kilometers and 120mm mortars about 7.5 kilometers.
The U.S. Army is buying over 800 HIMARS vehicles along with 100,000 GMLRS rockets, most of them fitted with an 89 kg (196 pound) high explosive warhead. About half of that is actual explosives. These have been used with great success in Iraq and Afghanistan, where nearly two 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.
The 120mm mortar round has about 2.2 kg (5 pounds) of explosives, compared to 6.6 kg (15 pounds) in a 155mm shell. The smaller explosive charges limits collateral damage to civilians. But in Afghanistan it is more common to need a large bang (which GMLRS can deliver). Excalibur was more suited to Iraq, but the American troops have left there and all the action is in Afghanistan. Moreover, there are a lot of precision weapons readily available to the infantry that have small warheads. The Javelin missile has a 4 kg (nine pound) warhead, and the larger TOW has a 5.9 kg (13 pound) one. The Hellfire missile has a 9 kg (20 pound) warhead. The air force also has its SDB (114 kg/250 pound small diameter bomb, carrying 23 kg/51 pounds of explosives).
Meanwhile, there is still demand for unguided 155mm and 120mm shells. There are times when you need firepower over a large area (several hundred meters by several hundred meters), and for this unguided shells do the job best and cheapest.
In response to this competition, the Excalibur manufacturer has created a model that can be used in 127mm naval guns. These are found in hundreds of warships and enable these ships to use their 127mm guns to accurately hit targets over 40 kilometers inland.