The U.S. Army has finally allowed its latest upgrade of the 50 year old M109 self-propelled 155mm howitzer to go into production. Initially 18 of the new 27 ton M109 PIM (Paladin Integrated Management program) will be produced, along with 18 of the 26 ton armored M992 CAT (Carrier, Ammunition, Tracked) ammunition carrier vehicles. These carry 90 rounds (the M109 carries 39) and have a crew of 3. Each pair of vehicles cost about $14.5 million. The M109 PIM has been in testing and revision (from problems found during tests) since 2011.
Despite the popularity of the M109, this design is half a century old and the U.S. has long been seeking a replacement, without much luck. For example, in 2009, the U.S. Army cancelled its second attempt (the XM1203 NLOS-C) to develop an M109 replacement. The third attempt was the PIM. That means the army is going to rebuild about 60 percent of its existing 900 M109s, rather than trying to come up with another new design. But PIM is quite an extensive upgrade. It uses the same chassis as the M2 Bradley infantry vehicle and a new engine control system. Remaining is the cab and gun mounts from the Paladin. From the XM1203, the automatic rammer, but not the automatic loader, is used. 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 includes new electronics and numerous small improvements, many based on user suggestions. This makes the M109 PIM competitive with some new European self-propelled 155mm howitzers.
The NLOS-C was to have been the first of the 8 MGV (Manned Ground Vehicle) systems to enter service in 2009, as part of the FCS (Future Combat System) program. But the FCS lost its focus, budget discipline, and Congressional support. It was cancelled in 2009. Before that the the prototype NLOS-C was cobbled together in 6 months in 2002, after the new (and very high tech and high priced) Crusader SP artillery system was cancelled. The 45 ton Crusader used an autoloader and an engine similar to the one used in the M-1 tank. With the end of the Cold War in 1991, Crusader was eventually deemed too heavy and too expensive. The NLOS-C used some Crusader components but was closer in size to the M109.
Although the M109 has been frequently updated, the NLOS-C incorporated many more new technologies. This included an auto-loader (from the Crusader) and a more modern 155mm gun and an APC chassis with a hybrid-electric engine (to reduce fuel consumption). This all weighed 23 tons and the NLOS only had a 2 man crew, compared to 5 in the 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 NLOC-C also got a lot of new electronics. 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 (operating as one would in combat) began in 2007, with the 6 prototypes.
One problem that quickly appeared was the ability of the 2 man crew to hold up during 24/7 operations. The then current M109A6 has enough people to take care of maintenance, standing guard, and, basically, always having 1 or 2 people rested and alert. Not so easy when you only have 2 guys. One solution was to have 2 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. PIM has a crew of 4, compared to 5 in the M109A6 and earlier models.
One of the things that helped kill the NLOS-C was the new GPS guided Excalibur shell. This smart shell entered service in 2007 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, meaning 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.
In the current war on terror, even the M109 has not been used much. The lighter, towed, M777 has proved more useful, especially when using the Excalibur shell. Currently, the army plans to keep PIM versions of the M109 around until 2050. 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.
The army plans to acquire over 500 PIMs, reflecting the impact of the Excalibur shell and the number of older M109s that are still fit for service. In the last decade, because of the growing use of smart bombs and GPS guided rockets and shells, the U.S. Army has cut the number of artillery weapons roughly in half. This ends a century of artillery tactics and technology, which featured large scale use of unguided shells fired at targets the gun crews could not see (indirect fire). Such tactics were radical and new a century ago and reached their peak during the World Wars, where individual battles often saw bombardments lasting days and expending millions of shells and rockets. All that is gone now and an era has ended.