July 2, 2022: The U.S. Army ERCA (Extended Range Cannon Artillery) is stalled because of reliability problems with the new cannon itself. Eighteen months ago, the ERCA prototype achieved a decade old goal of using a longer barrel cannon firing an extended range Excalibur GPS guided shell to accurately hit a target 70 kilometers distant. Over a decade ago it was realized that this required three new technologies. The primary need was a version of a reliable GPS guided artillery shell, like Excalibur, that could handle the more difficult task of keeping the shell on course over such a long range. The first version of Excalibur only worked at ranges between 20 and 25 kilometers. Second, there had to be a longer barrel 155mm artillery system that could fire the longer-range Excalibur shell. Finally, there had to be a new propellant that could provide the power to push the ERCA Excalibur out to 70 kilometers.

A longer-range Excalibur shell began development in 2010 and by 2011 Version 1A-2 of Excalibur was approved for combat use. During tests Excalibur 1A-2 accurately hit targets 40 kilometers distant. During its first combat use in 2012, a U.S. Marine Corps M777 155mm lightweight towed gun hit a target 36 kilometers away using Excalibur 1A-2. During development of Excalibur 1A-2 it was noted that, with a longer barrel gun and more powerful propellant, Excalibur could hit targets at least 60 kilometers and theoretically 70 kilometers away. Even with the short range of the original Excalibur, the GPS guided shell was quickly accepted as an essential weapon.

A more difficult problem was obtaining a new 155mm gun with a longer barrel. The relatively new and popular 4.2-ton M777 lightweight howitzer had a 155mm/32 barrel. That means the barrel length is 32 times 155mm or 5.1 meters (16.7 feet) long. The first long barrel experiments resulted in the longer XM907 barrel for the M777. This was a 155mm/52 barrel which was 8.1 meters (26.4 feet) long. XM907 worked, but was not practical for the towed M777 howitzer.

Another long barrel, the M1299 was built. This was a 155mm/58 barrel which was 9 meters (29.3 feet) long, and designed to be used in the latest version of the Paladin 155mm self-propelled howitzer. Normally the Paladin carries a 155mm/39 barrel that is 6.05 meters (19.3 feet) long, but similar vehicles have had longer barrels and been successful. An M1299 barrel on a M109A7 Paladin was used for the initial 2020 tests and it worked well in late 2020 tests that sent a GPS shell 70 kilometers.

A new XM1113 propellant system was first used with the long-barrel Paladin in early 2020 and was able to send a shell 65 kilometers. The XM1113 uses the decades old RAP (Rocket Assisted Projectile) technology that has been updated to provide unprecedented ranges of up to 70 kilometers. Such extreme ranges were not practical before GPS guided shells became available as the longer range, the unguided shell accuracy gets worse. The late 2020 test showed that Excalibur could put shells on targets 70 kilometers away. Only one of the three XM1113/Excalibur shells fired hit the target. The other two missed because the Excalibur guidance system was not able to handle some weather conditions, like exceptionally heavy winds. Excalibur can be tweaked to deal with that and more tests were conducted in 2021 to verify that the 70 kilometers Excalibur is reliable and ready for production. The longer barrel M109A7 was to enter service with the new Excalibur shell by 2023. Then it was discovered that the longer barrel (including the shell loading mechanism) had reliability problems. This has delayed final testing and approval indefinitely until the reliability problem can be fixed.

There are already vehicles similar to the M109 with longer barrels, although not quite that long. From past experience the longer barrel on a self-propelled howitzer chassis is no big thing. Making all the modifications to the recoil system, breech, and interior of the M109 did not require any new technology. Now it turns out that some new tech is required and if that cannot be obtained soon and at an affordable cost the 70 kilometers ERCM is dead. A shorter barrel, providing less range, might be acceptable if it can be developed in time and without costing so much that the ERCM Paladin becomes another new weapon that was canceled because it was too expensive to procure in useful numbers.

The longer barrel and 70-kilometer range of the Excalibur shell was a big deal for the Paladin, which was seen as a system eventually being replaced by cheaper, more effective artillery. During the fighting in Iraq and Afghanistan, the M109 was not used much. The lighter, towed, M777 has proved more useful, especially when using GPS guided shells. The army plans to keep updated Paladin versions of the M-109 around until 2050. The army planned to acquire as many as 500 M109A7 Paladins by 2027, reflecting the impact of the GPS guided shells, and the number of older M109s that are still fit for service.

The primary competition for ERCA equipped Paladin is the HIMARS (High Mobility Artillery Rocket System) vehicles that carry six GMLRS (GPS/INS guided MLRS). Ukraine knew of the success of the HIMARS vehicle and the capabilities of the GMLRS rockets. The latest version of the rocket can hit targets up to 85 kilometers away using INS/GPS (Inertial Navigation System/Global Positioning System) guidance. The INS component is important because it takes over if the GPS signal is lost due to jamming or when mountainous terrain blocks GPS as the rocket approaches the target. Over the last two decades INS has become more accurate. Russia has been a major source of GPS jammers since the 1990s. Two East Europe NATO members (Romania and Poland) use HIMARS. Several other NATO countries use HIMARS or the larger tracked MLRS vehicle (M270) that carries two pods. HIMARS is gradually replacing these. The HIMARS truck-mounted GMLRS system is ideal for Ukrainian artillery tactics, which currently use individual self-propelled artillery to fire unguided shells at targets up to 40 kilometers away. This avoids return fire from the Russians, who are more vulnerable to Ukrainian tactics because Russia still employs mass artillery fire from batteries (six guns) or battalions (three batteries).

Each HIMARS system is carried in a 12 to 16-ton 6x6 truck with the heavier version having armored (against small arms fire and shell fragments) crew cab. The vehicle carries one MLRS (Multiple Launch Rocket System) six rocket pod instead of two in the original larger, tracked, MLRS vehicle. Initially, a major attraction was that a HIMARS truck could fit into a C-130 transport (unlike the 22-ton tracked MLRS) and was much cheaper to operate. The HIMARS vehicle can move at up to 85 kilometers an hour on paved roads and travel 480 kilometers on internal fuel. In 2016 it was revealed that HIMARS vehicles in American service had reached a million operational hours with a 99 percent readiness rate. The tech HIMARS used enables HIMARS to operate (move, receive a target order and launch the GMLRS) using as few as one of the normal three-man crew.

The first HIMARS entered service in 2005, about a year after GMLRS did. The two new innovations worked well together and were a major reason for the success of the GMLRS and the HIMARS rocket launcher. The U.S. no longer buys the tracked MLRS or unguided MLRS rockets. An MLRS pod with six GMLRS weighs 2.8 tons and has attracted a lot of export orders.

The 309 kg (680 pound) GMLRS 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 backup INS/inertial guidance system) to find the target location it was programmed with. With GPS the GMLRS will land within a few meters of the GPS coordinates. If the INS has to be used, that triples to about ten meters. In 2008 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. One HIMARS vehicle can provide precision fire support over an area of about 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. By way of comparison, Excalibur (GPS guided 155mm shell) now has a max range of 55 kilometers, or 70 kilometers with the ERCA cannon.

GMLRS meant the MLRS fire control system was upgraded to handle precision targeting rather than just hitting a general area. Since 2004 over 3,000 GMLRS rockets have been fired in combat with 98 percent accuracy (hitting the target) and over 50,000 have been produced. GMLRS rockets cost about $100,000 each initially and the current cost (a 2021 order) is $110,000 even after several upgrades. This is cheaper than GPS equipped 155mm artillery shells because these shells generate a lot more stress as they leave the gun barrel. A more affordable ($12,000 each) GPS guided shell is available using the ATK fuze, which is screwed into the front of an unguided 155mm shell. The ATK approach is somewhat less accurate than Excalibur shells but that has been found acceptable in combat situations. Despite that HIMARS and GMLRS rockets are preferred and the popularity of HIMARS meant even less work for tube artillery, which was considered “king of the battlefield” since the 17th century. Export demand for HIMARS has meant the U.S. manufacturer has had to resume production for the growing number of foreign customers. This was again affirmed in Ukraine, which is waiting for the new version of GMLRS, which can be used in HIMARS and has a range of 150 kilometers. In combat, tube artillery can no longer compete when range and accuracy are the key factors.