The U.S. Army is seeking to inexpensively develop a longer range 155mm artillery weapon, using GPS guided shells to hit targets 70 kilometers distant. Called the XM907, the primary obstacle is financial, not technical. That’s because the last time the U.S. sought to do this (very long range 155mm gun with GPS guided shell) the project was for the U.S. Navy and the weapon was the 155mm AGS (Advanced Gun System) firing the LRLAP (Long Range Land Attack Projectile) GPS guided shell, which during tests hit land targets 83 kilometers distant. It was only in 2011 that LRLAP, after six years of development, had its first successful test firing. The AGS was designed to fire GPS guided shells up to 190 kilometers. That GPS guidance system enables the shells to land inside a 50 meter (155 foot) circle at that extreme range. The AGS shells carry 11 kg (24 pounds) of explosives. The AGS uses a water cooled barrel, so that it can fire ten rounds a minute for extended periods. Each AGS on the DDG 1000 carries 335 rounds of ammo, which is loaded and fired automatically. The AGS shell was originally supposed to enter service in 2015. It was cancelled in 2016 because the shells would cost $800,000 each for the six AGS guns in service with the Zumwalt destroyers. Zumwalt was too expensive and only three were built. Each had two of these 155mm that are essentially useless. AGS was developed to provide firepower for marines but the marines did not seem disappointed when the AGS failed to show up. The marines already had cheaper alternatives.
So does the army but undismayed by that the army went ahead with the initial XM907 work. This was done using the towed M777 155mm gun. This is a 4.2 ton weapon and adding the longer barrel and modifications to the breach and recoil system turned it into a 5 ton weapon that was too long to effectively tow around. The M777 has a 155mm/32 barrel. That means the barrel length is 32 times 155mm or 5.1 meters/16.7 feet long. The XM907 barrel has a 155mm/52 barrel (barrel length is 52 times 155mm or 8.1 meters/26.4 feet long). That is not a problem because the current M109 howitzer can handle the longer barrel. There are vehicles similar to the M109 with longer barrels, although not quite that long. But from past experience the longer barrel on a self-propelled howitzer chassis no big things. Making all the modifications (to the recoil system, breech, and interior of the M109 might be more expensive than expected. But that is not the main potential problem. That would be the cost of the guided shell.
The Excalibur GPS guided shell (with the GPS built in) cost $70,000 each in 2014, which is down from $150,000 each when Excalibur first entered service in 2007. Ultimately the price is to get down to $50,000, which some say has already been achieved if you don’t count development costs. Meanwhile an even cheaper solution appeared. In 2014 the army began using the XM1156 PGK (Projectile Guidance Kit). 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. The original version was much less precise than Excalibur. That is, the first PGKs only ensured 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 did not explode. The first version of PGK was subsequently tweaked so that by 2012 it landed within 32 meters. The most recent version has been further improved the land the PGK guided shell within 12 meters. This version also fixed reliability problems and now the PGK is 94 percent reliable. Unfortunately the troops still prefer Excalibur. As a result of that and overall cuts in the army budget, the number of PGK fuzes to be bought in 2015 was reduced sharply (from 4,857 to about 2,000). This means the price of a PGK won’t hit its goal of $10,500 and will instead be closer to $15,000 each. At that time Excalibur was down to $70,000 per shell. Ultimately the PGK won out because when you have to use a lot of PGKs (as the U.S. Marines did with their M777 howitzers in the battle to take the ISIL capital Raqqa in 2017) the PGK is an excellent solution.
If the PGK works with the XM907 and its longer (up to 70 kilometers) range shells the army might have something. But then you have to ask the question; why develop a new XM907 when you already have 227mm GMLRS guided rockets with the same range. These rockets have been used extensively in combat, are reliable and that is one of the reasons the U.S. Army largely abandoned long range artillery guns in the 1990s. Same deal with the marines and the failure of the LRLAP. In fact it was pointed out to the navy that they could equip the Zumwalts with GMLRS. After all the Israelis adapted some of their GPS guided rocket systems to be fired from their warships (or any ship). But the navy would rather not hear about fixing the Zumwalts anymore.
The reason for developing a longer range 155mm howitzer is because the Chinese and Russians are up to something similar. So it must be something we need. After all if the enemy has longer range artillery and you are out of guided rockets and such you are screwed. Unless you develop a similar artily weapon (and extended range shell to make it all work). Many people in the artillery community wonder what is going on here. They are not alone.
Since the end of the Cold War in 1991 the U.S. Army has drastically reorganized and reduced its artillery force. At the end of the Cold War most artillery was conventional “tube” artillery. That meant towed 105mm, 155mm, 203mm howitzers and self-propelled 155mm howitzers. The MLRS, a 16 tube 227mm unguided rockets was just entering service when the Cold War ended. In the 1990s it became obvious that smart bombs (JDAM) first used in the 1991 Gulf War, were more effective than artillery and that led to a major shift away from using artillery. By 2004 over 40 tube artillery battalions had been disbanded.
Another major change in 2004 was the introduction of the GMLRS (GPS guided MLRS) rocket. Like the unguided version, the GMLRS are packaged and used in containers (pods) holding six rockets each. Since then over 2,000 GMLRS rockets have been fired in combat. GMLRS rockets cost about $100,000 each and have been very successful. That has meant even less work for tube artillery, which had dominated the battlefield since the 17th century.
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 the target location it was programmed with. In 2008 the army tested GMLRS at max range (about 85 kilometers) and found that it worked fine. This enables one MLRS/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 MLRS/HIMARS vehicle), and fundamentally changes the way you deploy artillery in combat. By way of comparison, Excalibur (GPS guided 155mm shell) has a max range of 37 kilometers, and 120mm mortars about 7.5 kilometers.
At the moment there is work underway on a new GMLRS design that adds control fins to the rear of the rocket and, with the addition of a new rocket motor design, would extend GMLRS range to over 150 kilometers. This improved GMLRS is much less risky (from a technical point of view) than the longer range 155mm gun and shell.
Another reason for the success of the GMLRS is the HIMARS vehicle. 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.
Most of the GMLRS rockets are fitted with an 89 kg (196 pound) high explosive ("unitary") warhead. About half of that is actual explosives. That's twice as much explosives as the air force 130 kg (285 pound) SDB (Small Diameter Bomb). A 155mm artillery shell has 6.6 kg of explosives, and the 500 pound (227 kg) bomb has 127 kg of explosives, which produced an excessive blast for many urban combat situations. The GMLRS seemed to be just right most of the time. In 2011 a GPS guided 120mm mortar shell entered service. This shell has about 2.2 kg (five pounds) of explosives in it and has become popular for situations when you want pinpoint accuracy in areas with nearby civilians.
GMLRS has been used with great success in Iraq and Afghanistan, where most 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 HIMARS only carries six rockets, that's often enough to last for days, even when there's a lot of combat.
Noting the success of GMLRS, Israel, Russia and China have developed and put into service their own GPS guided rocket designs. Russia has long led in the design of new rocket systems was is playing catchup when it comes to using guided rockets. The multiple rocket launcher was first developed by the Russians before World War II as a cheap alternative to massed artillery fire by individual guns. Long seen as a supplement to regular artillery, the introduction of the high tech U.S. MLRS rocket system in the 1980s began to make a lot of conventional artillery obsolete even before GMLRS came along. Of course, artillery has always been ripe for innovation. The U.S. 175mm gun, introduced in the 1960s, was rendered obsolete in the 1980s with the introduction of special long range ammo for the 203mm (8 inch) howitzer. The U.S. Army stopped using the 175mm gun in the 1970s. When the MLRS entered service, one of the three batteries in each division's 203mm howitzer battalion was equipped with MLRS units instead. But MLRS proved so effective that the 203mm howitzer battalion became an MLRS battalion and the 203mm gun was dropped by the U.S. Army.
There were always non-divisional MLRS battalions, as the MLRS was seen, from the beginning, as an ideal weapon for massed artillery fire. The Gulf War allowed the MLRS to show off what a potent weapon it could be. The larger rockets also provided room for more complex payloads (cluster and "smart" munitions) and guidance systems. This was another example of how technology can transform an old weapon. While the Russians have been using rocket launchers for over 70 years, they never got around to enhancing their effectiveness with a lot of technology until recently and then only because they noted others were doing so and succeeding.