April 24, 2020: After three decades of effort the U.S. Army finally began production of a new 155mm SP (self-propelled) howitzer. At a cost of $4.8 million each, the first 48, of 133, new M-109A7 vehicles will replace 1960s era M109A5 vehicles. The M109A7s are nicknamed Paladin and during a decade of development were also known as the M106A6 PIM (Paladin Integrated Management program). It was actually a lot more complicated than that but now the army has the mobile artillery it could have had twenty years ago.

The first M109 entered service in 1963 and it proved so successful that it was ultimately adopted by most NATO countries and dozens of other nations as well. Including the many foreign license-built models, about 9,000 have been built so far. About a dozen nations still use it, often as improved models that were only used by the nation that developed a particular upgrade.

Despite the popularity of the M109 the United States has been seeking a replacement since the 1990s without much success. The first attempt, a Cold War era design called Crusader was too expensive, too heavy and canceled in 2002. In 2009 the U.S. Army canceled its second attempt; the XM1203 NLOS-C (Non-Line-of-Sight Cannon). The third attempt was the PIM and, fortunately, it worked.

In the meantime, technology had made most conventional (towed or self-propelled) artillery obsolete. While the United States had over 2,400 M109s in service in the late 1980s, when the Cold War ended, now the army can get by with about twenty percent, or less, of that number. In the 1990s the growing use of smart bombs and the post-Cold War reduction in armed forces sharply reduced the need for the M109. After 2000 new tech reduced the need for artillery still further with the introduction of GPS guided artillery shells and rockets. There were also a lot more ATGMs (anti-tank guided missiles) in infantry units and, lacking tanks to shoot at, the ATGMs proved to be life-savers when used against enemy forces in buildings or fortifications. For aircraft and helicopters, the lighter 48 kg (hundred pound) Hellfire missile replaced larger and heavier ones as well as a lot of artillery support. In short, there was a lot less demand for conventional (unguided shells) support.

During all these technical and tactical changes the army kept trying to design an acceptable replacement for the M109. The first attempt, was the Crusader, a larger vehicle that weighed 40 tons and cost $15 million each. The entire program was to cost $11 billion and that was more than the post-Cold War army budget could afford. Crusader could fire 155mm artillery shells farther, faster and more accurately than the existing M-109A6 but so what. The Crusader cancellation was said to be the victim of the end of the Cold War, but it was also a victim of the decades long struggle between the "smart munitions" (like the MLRS rockets with smart munitions and GPS bombs) and "smart weapons" (like the Crusader.) Smart munitions for tube artillery (like the Crusader) did not become reliable and affordable enough for wide use until 2008. An early failure was the 1980s Copperhead guided anti-tank round. They got it to work and some were used during the 1991 Gulf War but no one was impressed because it was too damn expensive. The 45 ton Crusader suffered from similar problems. It was too heavy to get anywhere in a hurry. It's easier to fly in MLRS (rocket launcher vehicle) or towed 155mm guns. Work continued on "smart shells" and six years after Crusader was canceled, the affordable and effective guided 155mm shell was in wide use. Crusader was a Cold War era design that was too expensive, too complex, too late and ultimately irrelevant.

The second M109 replacement effort was NLOS-C, which was to enter service in 2009 as part of the FCS (Future Combat System) program. Instead, NLOS-C was canceled in 2009 because the FCS project lost its focus, budget discipline and Congressional support. It was not for want of effort. In 2002 the prototype NLOS-C was cobbled together in six months after the Crusader was canceled. Although the M109 has been frequently updated, the NLOS-C incorporated many more new technologies. This included an auto-loader (from the Crusader), a more modern 155mm gun and an APC chassis with a hybrid-electric engine that reduces fuel consumption. Some of the electronics developed for Crusader were also used in NLOS-C. This all weighed 23 tons, about the same as the M-109. But the NLOS only had a two-man crew, compared to five in the M-109A6, and seven in the 1960s M109.

The final version of the NLOS-C was to be heavier (about 27 tons), because more defensive systems were added to reflect experience in Iraq. The vehicle carried 24 rounds of 155mm ammo. Congress originally demanded that NLOS-C be in service by 2008, but development needed a few more years. Field testing, as in operating as one would in combat, began in 2007 using six prototypes.

One remaining problem was uncertainty about the ability of the two-man NLOS-C crew to hold up during 24/7 operations. The M-109, with a five-man crew, has enough people to take care of maintenance, standing guard, and always having one or two people rested and alert. This is not so easy when you only have two guys. One solution was to have two or more crews per vehicle as combat aircraft, and some warships, have done for years. The off-duty crews would be back with the support troops. The NLOS-C never had to fix the two-man crew problem because it was canceled before the two-man crew was put to the test in a combat zone. PIM had a crew of four, compared to five in the Paladin M-109, which was expected to be enough and it is.

One of the things that helped kill Crusader also diminished enthusiasm, and patience for the NLOS-C was the new GPS guided Excalibur shell, which began development in the early 1990s and by 2002 was working but in need of refinement. This smart shell entered service in 2008 and changed everything. Excalibur has worked very well in combat, and this is radically changing the way artillery operates. Excalibur means 80-90 percent less ammo has to be fired to destroy a target. This means less wear and tear on SP artillery, less time needed for maintenance, and less time spent replenishing ammo supplies, and more time being ready for action.

By 2009 this left the army with a list of proposals for more upgrades to the M109A6 howitzer. The third attempt to replace the M109 consisted of the PIM (Paladin Integrated Management program). That means the army was going to rebuild some of its existing 900 M109 Paladin self-propelled 155mm howitzers, rather than trying to come up with another new design. In addition, many new M109s would be built to the new standard, which came to be known as the M109A7.

PIM used the same chassis as the M-2 Bradley infantry vehicle plus a new engine control system. Added to that was the cab and gun mounts from the M109A6 Paladin. From the NLOS-C came the automatic rammer, but not the automatic loader. So troops will still have to manually load the propellant and 41 kg (90 pound) shell, but the semi-automatic rammer will then push the propellant and shell into the firing chamber and close the breech. Automating this part of the process improves accuracy somewhat, because when troops manually shoved (rammed) in the propellant and shell, they often applied too much, or too little, pressure and left the shell out of position by a tiny bit, just enough to hurt accuracy. PIM also got new electronics, and numerous small improvements, many based on user suggestions. Not all the proposed upgrades were implemented immediately, but enough of them were to satisfy M109 users. The M109A7 made Paladin competitive with some new European self-propelled 155mm howitzers. The PIM is also heavier, at 35 tons and the new chassis can support up to 50 tons. Even at that weight, PIM is as fast as the existing M-109 and more maneuverable.

During the fighting in Iraq and Afghanistan, even the older M109 was not used much. The lighter, towed, M777 has proved more useful, especially when using the GPS guided shells. The army plans to keep PIM/Paladin versions of the M-109 around until 2050. The army plans to acquire as many as 500 M109A7 by 2027, reflecting the impact of the GPS guided shells, and the number of older M109s that are still fit for service. The M109 was a solid design, which is pretty clear from how difficult it's been to come up with a replacement. So, in the end, the army replaced the M109 with another M109 upgrade. Along with the new M109A7 will come a hundred or so of the upgraded M992A3 CAT ammo resupply vehicle which is basically an M109 without the turret and space to carry nearly a hundred rounds of 155mm ammo as well as automated systems. These vehicles can quickly transfer ammo to a M109, which can only carry 36 15mm shells and propellant. Fewer M992s are needed because M109s fire fewer of the guided shells. The GPS shells have also been improved with Excalibur complemented, and often replaced by the new M1156 PGK guided shell. 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 shell. 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 by using a timer or small radar. No one had been able to put GPS guidance in such a small package before but many kept 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 the shell so it did not explode. The 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. At that point, Excalibur became a premium item, which was more accurate than PGK but nearly twice as expensive. PGK proved itself in Syria where small numbers of American towed howitzers supported the Syrian Kurd forces that took the ISIL (Islamic State in Iraq and the Levant) capital Raqqa in 2017. ISIL thought they could defeat the attackers by defending many hidden positions inside the city. PGK made that ineffective. Most of the civilians had fled Raqqa and once a group of ISIL fighters was encountered one or two PHK shells would kill them. This broke the morale of many ISIL fighters, who fled Raqqa rather than fight to the death without much chance of hurting any of the attackers.