Artillery: Cheaper GPS Shells


December 19, 2012: The U.S. Army has successfully tested a new, cheaper, way to add GPS accuracy to 155mm artillery shells. The current Excalibur shell costs over $100,000 each and has GPS guidance built in. The new XM1156 Precision Guidance kit costs about half as much as Excalibur and is screwed into the front of the shell like a fuze would be. A similar system (by the same outfit producing the XM1156) for 120mm mortars was introduced last year by the U.S. Army and has been popular (and successful) with the troops.

Meanwhile the army has found that GPS guided shells were more successful than anticipated, which enabled orders for these weapons to be reduced. Excalibur shells were used less frequently than expected in part because the high accuracy often meant that only one Excalibur shell had to be used. Another reason for lower demand was the fact that other precision munitions often destroyed targets before Excalibur got a chance to. The GPS guided MLRS (GMLRS) rocket has been very popular and often the first choice of commanders in need of some precision firepower. The army also uses a lot of laser guided Hellfire missiles, fired from AH-64 helicopter gunships. In addition to the reduction in Excalibur production, the army has cut the number of GPS guided 120mm shells on order.

The Excalibur and the ATK 120mm guided shell are facing a lot of competition from GMLRS, which cost about the same as an Excalibur shell but has 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 rockets, 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 that entered service eight 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 backup inertial guidance system) to find its target. The army soon found that GMLRS was just as accurate at max range (about 85 kilometers). 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. Excalibur has a max range of 37 kilometers, and 120mm mortars about 7.5 kilometers.

Nearly all GMLRS rockets are fitted with a 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 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. The army stopped buying unguided rockets three years ago. 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. One GMLRS will often get the job done, from destroying to demoralizing the Taliban foe.

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 charge limits collateral damage to civilians. But in Afghanistan it was more common to need a large bang (which GMLRS can deliver). Excalibur was more suited to Iraq but American troops have left there, and all of the action is in Afghanistan. Moreover, there are a lot of precision weapons, with small warheads, readily available to the infantry. The Javelin missile has a 4 kg (9 pound) warhead, and the larger TOW has a 5.9 kg (13 pound) warhead. The Hellfire missile has a 9 kg (20 pound warhead). The air force also has its SDB, a 114 kg (250 pound) small diameter bomb, carrying 23 kgs (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. But precision (or “smart”) shells are the future and these weapons are expected to continue getting cheaper.




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