While the GPS guided Excalibur 155mm artillery shell revolutionized the use of artillery when it appeared in 2005, it is being displaced by a smaller, less capable but much cheaper alternative; M1156 PGK (Projectile Guidance Kit) fuze. In mid-2017 the U.S. Army ordered another 5,600 PGK fuzes for 155mm artillery shells. A year earlier M1156 was cleared for mass production. Up until mid-2016 4,800 PGKs has been produced under a limited production arrangement. But because of growing export orders and the fact that PGK costs 85 percent less than the slightly more accurate competition the U.S. Army has decided to stock up on the PGK in a big way.
With PGK the army has two GPS guided artillery shells; the older, more accurate and expensive M982 Excalibur and the new M1156 PGK. The advantage PGK has is that the GPS guidance is not built into a shell but instead it is a slightly heavier (about 1.4 kg/3 pounds) and larger fuze that screws into the front of a 155mm. This PGK fuze contains a GPS and small fins to guide the shell to a precision hit. Normally the fuze just controls how the shell will explode or when (using a timer or small radar). No one had been able to put a GPS guidance in such a small package but many have been trying for several decades.
The original (2009) version of PGK was much less precise than Excalibur and could only ensure that the shell landed within 50 meters (160 feet) of the target. If it did not hit within 150 meters, PGK deactivated and the shell dose not explode. In original version of PGK was subsequently tweaked so that by 2012 it landed within 32 meters (100 feet). By 2012 PGK was been further improved to put a guided shell within 19 meters (60 feet). By 2015 accuracy was improved to 10 meters or less and the reliability problems largely eliminated as the PGK was now over 90 percent reliable.
Meanwhile early users noted that the less accurate PGK was often adequate for most missions requiring a guided shell. Potential export customers were particularly eager because they had plenty of 155mm shells and word of the PGK accuracy and reliability improvements had gotten around, especially “customer satisfaction” comments from troops who called in PGK fire during combat. The lower cost was a big deal because it meant units could have a lot more access to GPS guided artillery fire when using PGK fuzes. Excalibur was so expensive that it was made available in limited quantities.
Troops who had a choice still preferred Excalibur but in combat they found it didn’t make any difference most of the time and with PGK the artillery unit supporting the combat troops was likely to have more PGK fuzes than Excalibur shells. Moreover PGK continues to get cheaper while Excalibur is down to $70,000 per shell and seems to be stuck at that price.
Both Excalibur and PGK have revolutionized the use of artillery. An unguided shell will normally land within 267 meters of where it is aimed at maximum howitzer range (18 kilometers). An Excalibur shell always landed within 10 meters of the target (and often closer) but PGK was a lot cheaper, got to be nearly as accurate and turned any unguided shell into a GPS guided one. The U.S. Army sent the first PGKs to Afghanistan in 2013, after successful testing in the United States. The big question was how important would the troops find the accuracy and reliability differences between Excalibur and PGK. Initially the army bought 2,400 PGKs and the U.S. Marine Corps got 700. There is one export customer. Australia has ordered 4,000 PGKs and it was the Australians and other export customers who made PGK the preferred solution for GPS guided shells. The Australians had used Excalibur and were even more discouraged by the high price. But PGK was a bargain and more flexible in comparison to Excalibur.
By 2015 the U.S. Army was thinking of buying over 20,000 PGKs, but thought that would take a lot longer with the increasing budget cuts. The success of PGK in Iraq, Syria and Afghanistan plus growing demand from allies threatened by Russia or North Korea has made PGK a much more popular solution for those wanting GPS guided artillery shells and shrinking ammo budgets turned into demands that stockpiles be replenished and expanded.
When artillery units had used both they still preferred the more accurate and reliable Excalibur over PGK. But they also found PGK could do the job just as well as Excalibur simply by firing two PGK shells to ensure the target was hit. This was still cheaper (by more than half) compared to Excalibur
The manufacturer of Excalibur tried to cope by developing a dual mode version that all allows for use of a laser designator. This provides even more accuracy, usually putting the shell within a meter or two (less than seven feet) of the aiming point. Excalibur is often called in when precision is the main requirement and this dual mode version provides the greatest accuracy available with any guided munition. But this level of accuracy is rarely needed from 155mm artillery and the infantry often have guided missiles or helicopters armed with Hellfire to take care of the targets that required laser accuracy. Most of the time having PGK guided shells was good enough and often a lifesaver.
The Excalibur shell cost reached $70,000 each by 2014, which is down from $150,000 each when Excalibur first entered service in 2007. Ultimately the price was to get down to $50,000, which some say has already been achieved if you don’t count development costs. But as a practical matter the much cheaper and almost as accurate PGK means less demand for Excalibur and less likelihood that the per-shell price will come down. Meanwhile development work continues. In addition to the laser guidance option Excalibur shells had range increased from 25 to 40 kilometers. Because Excalibur uses a lot of Swedish technology the Swedes will continue development if the United States drops out. The U.S. Army spent billions to develop the highly accurate M982 Excalibur GPS/laser guided 155mm artillery shell. But because so many other weapons have shown up with the same kind of accuracy, Excalibur was not called on nearly as much as originally believed. Excalibur was less frequently used than anticipated and orders for these weapons had to be reduced. So far the army has bought or plans (thru 2016) to buy only 6,876 Excalibur shells.
There was less demand for Excalibur shells 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 or UAVs. 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.
The army wants to build up its stockpile of Excalibur and PGK, but because Excalibur got into service first and proved more accurate and reliable than the later PGK the army is stocking up on Excalibur first, and then the cheaper (and improving) PGK. Ultimately items like PGK will replace Excalibur, but for now Excalibur is the more mature and effective technology. But if there is a major war, the cheaper and easier to produce PGK will be the more practical choic because production can be increased more quickly and cheaply and the PGK is a lot easier and cheaper to store and transport.