The M109 is an American-made self-propelled 155 mm howitzer, first introduced in the early 1960s. It was upgraded a number of times to today’s M109A6 Paladin. The M109 family is the most common Western indirect-fire support weapon of maneuver brigades of armored and mechanized infantry divisions.
The M109 has a crew of six: the section chief, the driver, the gunner, the assistant gunner and two ammunition handlers. The gunner aims the cannon left or right (deflection), the assistant gunner aims the cannon up and down (quadrant). The M109A6 Paladin needs only a crew of four: the commander, driver, gunner and ammunition loader.
The British Army replaced its M109s with the AS-90. Several European armed forces have or are currently replacing older M109s with the German PzH 2000. Upgrades to the M109 were introduced by the U.S. (see variants below) and by Switzerland (KAWEST). With the cancellation of the U.S. Crusader, the Paladin remains the principal self-propelled howitzer for the U.S. for the foreseeable future.
The M109 was developed by the Ground System Division of United Defense LP (now BAE Systems Land and Armaments).
- Primary: M126 Cannon (or M126A1) 155 mm Howitzer (M109), M185 Cannon 155 mm Howitzer (A1/A2/A3/A4), M284 Cannon 155 mm Howitzer (A5/A6)
- Secondary: .50 caliber (12.7 mm) M2 machine gun, Mk 19 Mod 3 40 mm Automatic Grenade Launcher, or 7.62 mm M60, M240 machine gun or the British L4 machine gun
Hypervelocity Projectile (HVP)
In January 2016, the U.S. Army test-fired hypervelocity projectiles originally designed for use by U.S. Navy electromagnetic railguns and found that they significantly increased the gun’s range. The Army is looking into using the M109 Paladin firing the HVP for ballistic missile defense, as traditional missile interceptors are expensive and gun-based missile defense used for point defense would use artillery at a much lower cost per round. The HVP is capable of being fired out to 50 nautical miles (58 mi; 93 km) from a conventional cannon. It weighs 68 lb (31 kg) with a 46 lb (21 kg) flight body containing its guidance and warhead—less powerful, but more agile to hit small, high-speed targets. 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. During a test of the Air Force’s Advanced Battle Management System (ABMS) on 3 September 2020, an HVP fired from an Army Paladin howitzer successfully intercepted a BQM-167 target drone simulating a cruise missile.
Replaced the M126 Cannon with a longer barreled, 39 caliber M185 Cannon, increasing maximum range to 18,100 meters.
Incorporated 27 Reliability, Availability, and Maintainability (RAM) mid-life improvements. Most notably, the long barreled 155 mm M185 Cannon in the new M178 gun mount, ballistic protection for the panoramic telescope, counterbalanced travel lock, and the ability to mount the M140 bore sight alignment device. Stowage of 155mm rounds increased from 28 to 36 rounds; .50cal ammunition remained at 500 rounds. During M109A2 production, a slightly simplified version was also produced for export. This had minor internal changes and deleted the hull flotation feature. These were designated M109A1B.
M109A3 and M109A3B
M109A1s and M109A1Bs rebuilt to M109A2 standard respectively. Some A3s feature three contact arm assemblies, while all A2s have five.
M109A2s and M109A3s improved with Nuclear, Biological, and Chemical / Reliability, Availability, and Maintainability (NBC/RAM) improvements, including air purifiers, heaters, and Mission Oriented Protective Posture (MOPP) (protective) gear.
The traversing mechanism’s clutch is hydraulic, as compared to the electric mechanism on previous M109s, and features a manual override in the event of an electrical failure. The M109A4 also added an additional hydraulic filter, for a total of two. Also included is an improvement to the engine starting equipment, greatly improving the ability to start in an emergency.
Ammunition amounts remain the same as two previous models.
Replaces the 155 mm M185 Cannon in an M178 Mount with a 39-caliber 155 mm M284 Cannon in an M182 Mount, giving the A5 a maximum range of 22,000 meters with unassisted projectiles and 30,000 meters with Rocket Assisted Projectile (RAP) rounds. The vehicle can carry 36 complete rounds of ammunition and has a 440 hp engine instead of the standard 405 hp engine.
Various manufacturers have upgraded the fire control and other components of the M109A5. BAE Systems in York PA recently delivered 12 M109A5+ vehicles to Chile and 32 for Brazil.
Overall product improvement in the areas of survivability, RAM, and armament. This includes increased armor, a redesigned internal arrangement for safer ammunition and equipment storage, engine and suspension upgrades, and product 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) . The battery FDCs in turn coordinate fires through a battalion or higher FDC. This allows the Palladin to halt from the move and fire within 30 seconds with an accuracy equivalent to the previous models when properly emplaced, laid, and safed—a process that required several minutes under the best of circumstances. Tactically, this improves the system’s survivability by allowing the battery to operate dispersed by pairs across the countryside and allowing the howitzer to quickly displace between salvos, or if attacked by indirect fire, aircraft, or ground forces.
Ammunition storage is increased from 36 to 39 155 mm rounds.
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. It features inertial navigation system coupled with a new gun-laying system and more ammunition storage(40 rounds, 64 charges). The KAWEST (lit. Kampfwertsteigerung = upgrade of combat capabilities) requires only 6 crew members instead of 8, and is able to fire 3-round bursts within 15 seconds or maintain a constant firing rate of over one round per minute.
Upgraded Swiss PzHb (Panzerhaubitze) 79 and 88 (M109A1) are known as respectively PzHb 79/95 and PzHb 88/95.
Jointly developed by the Dutch firm RDM and the German firm Rheinmetall, the M109L52 was first revealed in 2002. The main improvement was replacing the M126 series gun with the longer 52-caliber cannon from the PzH 2000, thus the MTLS ammunition of the PzH 2000 can be used. In addition, improvements to the loading system were made. This resulted in an increase of the rate of fire to 9–10 rds/min from the original 3 rds/min, and this high rate of fire can be sustained for up to 2 minutes. A total of 35 rounds can be carried.
The current version in service with the Norwegian Army’s Artilleribataljonen. 126 M109Gs were acquired from West Germany between 1969–1971. They were then upgraded to the M109A3GN configuration during the latter half of the 1980s. In 2006, there were still 56 M109A3GNs in the Army’s inventory, meaning that at least 70 SPGs had been scrapped after the end of the Cold War. 14 of the M109A3GNs received additional upgrades in 2007, and were designated M109A3GNM. The upgrade includes, among other things, new intercom and new navigation and positioning systems. The M109A3GNMs are currently the only SPGs that remain in active service with the remainder of the M109s having been put in storage.
K55/K55A1 are South Korean variants of the M109A2, originally named KM109A2 with additional domestic augmentations, license-produced by Samsung Techwin. They are fitted with M178 155 mm 39 caliber gun, NBC protection, automatic fire extinguishing system, and a modified ammunition reception module for K56 automatic ammunition resupply vehicle. The Performance Improvement Program variant, K55A1, is a complete domestic overhaul of the K55 which is further augmented by Samsung Thales with modern digital ballistic computers, multifunctional data display and controllers, GPS navigation and target acquisition system, wireless datalink equipment, and upgraded fire control storage battery and power supply unit, to closely match the US military’s modernization of the Paladin into next-generation standard. Many improved technologies of the South Korean K9 Thunder were retrofitted on the K55A1. 1,040 howitzers of these variants were produced.
The newest M109 version for U.S. service is the M109A7, formerly known as the M109A6 Paladin Integrated Management (PIM). The M109A7 shares common chassis components with the Bradley Fighting Vehicle (BFV) such as the engine, transmission, and tracks. This creates commonality with other systems and maximizes cost-savings in production, parts inventory, and maintenance personnel. The M109A7’s on-board power systems harness technologies originally developed for the Non-Line-of-Sight Cannon; the electric drive is faster than the previous hydraulic system, and the automatic rammer more consistently rams the round into the gun for consistent velocities and better accuracy. It features a 600-volt on-board power system to accommodate additional armor and future networking technologies as they become ready. The M109A7 can sustain a one-round per-minute rate of fire and a maximum rate of fire of four rounds per-minute.
Weighing 78,000 lb (35,000 kg), the M109A7 is 10,000 lb (4,500 kg) heavier than its predecessor, and it has the capacity to grow to 110,000 lb (50,000 kg). Even with the weight increase, the M109A7 can travel faster than previous versions at 38 mph (61 km/h) and is more maneuverable than a BFV.
Prototypes of the vehicle underwent government testing in preparation for a Low-Rate Initial Production (LRIP) decision. The testing included RAM, mission and ballistic hull and turret testing. The M109A7 was slated to begin LRIP by 2013. The U.S. Army planned on procuring a fleet of 580 sets of M109A7 howitzers and M992A3 Field Artillery Ammunition Support Vehicles (FAASVs).
In October 2013, the Defense Acquisition Board approved the decision to start M109A7 production. The FY 2014 budget called for $340.8 million in Paladin funding, which would be two dozen vehicle sets at $14.4 million per vehicle. The Army plans to buy 133 vehicles in 66 one-half vehicle sets starting in 2014, although one M109A7 howitzer and two supporting M992A3 ammunition carriers will be destroyed during tests. A Full-Rate Production (FRP) decision planned for February 2017. On 31 October 2013, BAE received a $668 million contract to begin LRIP of the M109A7. The first M109A6 and M992A2 vehicles were disassembled and reassembled to M109A7 and M992A3 standard as part of LRIP beginning in summer 2014. LRIP deliveries began in April 2015. The contract for FRP was signed in December 2017 with 48 vehicles slated for construction. The Army plans to upgrade 689 Paladins to A7-standard.
The Army is looking to increase the capabilities of the M109A7. By introducing the new XM1113 rocket-assisted projectile (RAP), it can reach 40 km (25 mi) from the current 39-caliber barrel, and a planned barrel extension to 58-caliber can increase its range to 70 km (43 mi). 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. The Army is also working on an autoloader to increase sustained rate of fire to 6–10 rounds per minute. These improvements are being developed under the Extended Range Cannon Artillery (ERCA) program, with the upgraded system designated the M1299. The first ERCA cannons are planned to be fielded in 2023, with the autoloader fielding one year later.Another part of the ERCA effort is the use of a new super-charged propellant to fire the shells, which required redesigning the howitzer to handle higher pressures.
|Length||30 ft (9.1 m)|
|Width||10 ft 4 in (3.15 m)|
|Height||10 ft 8 in (3.25 m)|
|Crew||6 (2 Loaders, Gunner, Assistant Gunner, Commander, Driver)|
|Shell||separate loading, bagged charge|
|Caliber||155 mm L/39 caliber|
|Rate of fire||Maximum: 6 rpm
Sustained: 3 rpm
|Effective range||Conventional: 18 km (11 mi)
RAP: 30 km (19 mi)
|M126 155 mm Howitzer|
|.50 caliber (12.7 mm) M2 machine gun|
|Engine||Detroit Diesel 8V71T
450 hp (335.56 kW)
|216 mi (350 km)|
|Speed||35 mph (56 km/h)|