The M109 family is the most common Western indirect-fire support weapon of maneuver brigades of armored and mechanized infantry divisions.

With the cancellation of the U.S. Crusader, Non-Line-of-Sight Cannon and M1299 the M109A6 ("Paladin") will likely remain the principal self-propelled howitzer for the U.S. until a replacement enters service.

[7] According to video and photographic evidence compiled by the open-source intelligence website Oryx, as of 24 September 2024, at least 70 units of different variants had been lost (54 destroyed and 16 damaged).

Easily identified by its short barrel and a double baffle muzzle brake with a large fume extractor just behind it.

[12] Fielded in 1973, this modification replaced the M126 cannon with a 39 caliber M185, featuring a longer barrel while increasing maximum range to 18,100 meters.

The United States delivered two completed M109A2s to South Korea for operational review, and the Agency for Defense Development began to translate the data package and created field and maintenance manuals for soldiers.

South Korea wanted to produce every part of the vehicle domestically; however, due to the amendment bill by Rep. Samuel S. Stratton of New York, which established a limit for foreign military technology cooperation, the turret and the M185 cannon from Watervliet Arsenal were imported from the United States.

[5] Compared to the M109A2, besides 63 percent of parts being produced locally, K55 has a driver's night periscope and light exposure minimization device to enhance night-time operations as well as additional radio systems.

South Korea was expecting to export 72 K55s and four ammunition support vehicles to Brazil for $160 million over Belgium's offer, but the United States Department of Defense declined the request to avoid an arms race in the region.

In 1983, the German Army purchased 586 conversion kits from the FMS Corporation (now Marvin Land Systems) to convert its fleet of M109Gs to the M109A3G standard.

This includes increased armor, a redesigned internal arrangement for safer ammunition and equipment storage, engine and suspension upgrades, and improvement of the M284 Cannon and M182A1 Mount.

The greatest difference is the integration of an inertial navigation system, sensors detecting the weapons' lay, automation, and an encrypted digital communication system, which utilizes computer controlled frequency-hopping to avoid enemy electronic warfare and allow the howitzer to send grid location and altitude to the battery Fire Direction Center (FDC).

[30] This Swiss improved version produced by RUAG incorporates a new Swiss-designed L47 155 mm gun with an increased firing range of up to 36 km.

[39] Improvement of the Swiss Kawest variant, 133 in total were brought up to this standard: The K55A1 is a South Korean overhaul and modernization of the K55, augmenting the proven systems of the K9 Thunder and the K9A1.

[41] The upgrade was performed by Samsung Techwin, and the first vehicle was fielded by the South Korean Army in early 2011.

The improved suspension, involving a strut-type hydropneumatic buffer from Mottrol Co, Ltd., along with an enhanced chamber, allowed the vehicle to shoot K307 and K310 ammunition designed for K9 platform without laying spades at a maximum distance of 32 km.

This creates commonality with other systems and maximizes cost savings in production, parts inventory, and maintenance personnel.

[48] Prototypes of the vehicle underwent government testing in preparation for a Low-Rate Initial Production (LRIP) decision.

An additional XM1113 improvement over the legacy RAP round is the replacement of the high explosive, TNT, with an insensitive munition that is less volatile and less prone to unplanned detonation.

[56] Another part of the effort is the use of a new supercharged propellant to fire the shells, which required redesigning the howitzer to handle higher pressures.

[58] In January 2016, the U.S. Army test-fired hypervelocity projectiles originally designed for use by U.S. Navy electromagnetic railguns.

Modifications will be needed for the Paladin to effectively shoot the HVP, possibly including different propellant to achieve higher velocities, automated reloading systems to fire quickly enough to defeat salvo launches, improved barrel life, and a new fire control and sensor system.

[61] During a test of the Air Force's Advanced Battle Management System (ABMS) in September 2020, an HVP fired from an Army Paladin howitzer successfully intercepted a BQM-167 target drone simulating a cruise missile.

[69] The M1299 was a prototype self-propelled howitzer developed by BAE Systems in 2019 under the Extended Range Cannon Artillery (ERCA) program.

As a follow-up to the K55 program, Samsung Aerospace Industries prepared for licensing a local variant of the M992, featuring such modifications as NBC protection and an increase of ammunition storage capacity to 110 rounds, 116 packs of powders, and 132 primers.

[79] Later, the development completion schedule was delayed to 2011, while the total production amount was increased to 700 vehicles with a cost of 1.3 trillion KRW between 2012 and 2021.

[80] In September 2010, the Board of Audit and Inspection claimed that the Army was biased during evaluation, and demanded re-analysis of the project regarding inefficiency of the system.

The Defense Acquisition Program Administration (DAPA) ignored the Board and continued with the project while the Army purposely delayed complying.

[86] The US Army uses the Fire Support Combined Arms Tactical Trainer (FSCATT) in two versions, for initial and sustainment training of the M109A6 and M109A5.

[citation needed] The Dutch, Belgian, Thai, and Israeli Armies have various configurations of the Van Halteren Metaal M109 Howitzer Crew Trainer (HCT).