M108 - Light 105mm SP Howitzer

Light Self-Propelled 105mm Howitzer

NSN 2350-00-440-8810

This version had the T-196 development designation. It was designed at the same time as the M109. The weapon mounts a 105mm M103 howitzer with a small fume extractor but no muzzle brake. It was only produced in 1962 and 1963. The M108 is in service in Brazil, Spain, Taiwan and Turkey.

M109 - 105mm SP Howitzer

Self-Propelled 105mm Howitzer

NSN 2350-00-440-8811

The original production version of the M109 developed from the T-196, introduced in 1963. Fitted with a short (23-caliber) 105mm M126 howitzer with muzzle brake and a distinctive large "lazy D"-shaped fume extractor. Maximum M126 projectile range of 15,914 yd (14,600 m). The vehicle carried 28 rounds.

M109A1 - 155mm SP Howitzer

Self-Propelled 155mm Howitzer

NSN 2350-00-485-9662

The M109A1 mounts the longer M185 155mm gun and incorporates elevation, traversing and suspension improvements. It can fire a high-explosive round 19,800 yd (18,100 m). The M109A1 weighs 53,070 lb (24,070 kg) fully loaded and is 29ft 8-in (9.04-m) long including the barrel. The first M109A1 conversion kits were produced in 1972. The first converted from standard vehciles became operational in 1973.

M109A2 - 155mm SP Howitzer

Self-Propelled 155mm Howitzer

NSN 2350-01-031-0586

The M109A2 is a new production weapon which incorporated 27 mid-life improvements to the M109A1. The M109A2 variant howitzer featured many system improvements, including a redesigned rammer, improved recoil mechanism, engine operation warning devices, re-designed hatch and door latches, improved hydraulic system and larger turret bustle carrying 36 155-mm projectiles. Production began in 1978. About 850 were produced for the U.S. Army and Army National Guard. The M109A2 is still in current production under a technology transfer agreement between the U.S.A. and Samsung in South Korea, the K55 and K55A1. Since this collaboration, Samsung Techwin, or now Hanwha Techwin, has developed its own Howitzer, the K9. The K9 utilizes many parts that are similar or identical in design to the M109.

M109A3 - 155mm SP Howitzer

Self-Propelled - 155mm SP Howitzer

NSN 2350-01-031-8851

The M109A3 is a depot converted M109A1 incorporating the 27 mid-life improvements. The M109A3 had an improved M178 cannon mounting, boresight alignment driver and selected RAM and safety kits, which included a fuel system air purge, driver's instrument panel, bustle/rack, propellant stowage, torsion bar, counter-recoil buffer, and upper recoil cylinder. Introduced in 1980, most of the global M109 fleet were retrofitted to the M109A3 designation standard. The performance of the M109A3 is identical to the M109A2.

M109A4 - 155mm SP Howitzer

Self-Propelled 155mm Howitzer

NSN 2350-01-277-5770

The M109A4 designation was used for the 737 U.S. Army Reserve Howitzers re-fitted under the NBC and reliability, availability and maintainability (RAM) program completed in 1993. The system upgrades included in this specfic re-fit included:

• 180A electrical charging system
• Vane-axial fan assembly increasing cooling capacity and reliability
• Twin hydraulic filters to replace the single power-pack filter
• External power receptacle
• Crew compartment sub-floor drains for torsion-bar pockets
• Traverse mechanism upgrade of internal gearing and clutch and addition of hydraulic tubing and external clutch valve
• Rewire air cleaner switch to shut off when vehicle in neutral
• Add starter-circuit protection relay to prevent over-cranking
• Move slave-start receptacle to driver compartment
• Add protective covers over sensors mounted on engine hood

M109A5 155mm Howitzer

Self-Propelled 155mm Howitzer

NSN 2350-01-281-1719

The M109A5 was an upgrade of the M109A3 to the M109A4 standard with additional features including the Reserve Component/Modified Armament System (RC/MAS) that, with the installation of the M284 cannon assembly and M182 gun mount upgraded the weapons to the A6 variant standard. US Fleet upgrades were completed in 1994 and exports began in 1998. The M109A5 fields upgraded components providing greater durability. The powertrain was upgraded with a higher output (440HP), low heat rejection (LHR) engine and an improved transmission (Allison ATD-XTG 411-4A) for increased mobility. A4 features such as fire suppression, an over-cranking protection device to prevent starter burnout, a 180A alternator that extends battery life, the elevation/equilibrium cylinder and turret traverse clutch assembly are re-designed to reduce failures, protective covers for the engine electrical sensors to prevent accidental damage, relocated and easily accessible filters improve hydraulic power pack filtration, easier to replace track pads and external road wheel lubrication points simplify maintenance. The suspension system was strengthened and an external NATO power receptacle was added to allow the M109A5 to be electrically powered by the M992 Field Artillery Ammunition Support Vehicle (FAASV).

The M109A5 variant is the the most advanced "factory" variant of the original M109 production series in use by non-U.S.A. Armed Forces.

M109A5+ 155mm Howitzer

Self-Propelled 155mm Howitzer

NSN 2350-01-281-1719 (Same as M109A5)

The M109A5+ is the designation given to field upgraded M109A5 variants. Many manufacturers have fielded system improvements since the M109A5 which are designed to be incorporated into the exported M109A5 vehicles providing improved mobility, communications, battlefield integration and fire control. NSN Depot provides program management services, RESET and upgrade services for existing users of the M109A5 to provide M109A5+ capabilities including:

• Fire Control Upgrade
• Increased firing range of up to 36 km
• Burst Firing Capability (3 Rounds in 15 Seconds)
• Engine Upgrades and Improvement
• Transmission Upgrades and Improvement
• Suspension Upgrades
• Track Upgrades
• Communications Upgrades
• Battlefield Data Management
• Armor Augmentation
• Driver and Commander Assistance Systems
• Electrical System Upgrades (MIL-STD-1245A and better)
• Maintenance Systems, Facilities and Logistics Improvement (Higher MTBF)
• Crew Training Simulators

M109A6 Paladin - 155mm SP Howitzer

Self-Propelled 155mm Howitzer

NSN 2350-01-305-0028

The M109A5 Howitzer was the subject of several U.S. Army programs for improvement and sustainability ending in the merger of the Howitzer Improvement Program (HIP) and Howitzer Extended Life Program (HELP) into the M109A6 Paladin variant standard in 1989. The major improvements that define the A6 Paladin variant are:

• Upgraded gun mount that accepts a 39 and 58 caliber 155mm cannon
• Secure SINCGARS radios
• Paladin Digital Fire-Control System (PDFCS)
• Onboard diagnostic systems
• Increased ammunition load
• Additional armor: 5083 aluminum with composite spall liners and supplemental armor
• Upgraded engine and transmission

M109A6 Paladin Integrated Management (PIM) - 155mm SP Howitzer

Self-Propelled 155mm Howitzer

NSN TBD

The M109A6 PIM is the currently fielded variant of the M109 for the U.S. Army which integrates an upgraded M109A6 turret with a brand new chassis from BAE Systems borrowed from the M2/M3 Bradley Fighting Vehicle. This program, initiated in 2007, improves the viability and sustainability of the M109 fleet when integrated into Heavy Brigade Combat Teams (HBCT). The new powertrain and chassis allow the vehicle to maintain pace with other advanced heavy vehicles while provided spare parts commonality with newer generation vehicles.

The new all-welded aluminum armor chassis incorporates a Cummins 600-hp diesel engine and L-3 Combat Propulsion Systems HMPT-500 series automatic transmission. The new powerpack improves the power-to-weight ratio and top speed. The vehicle utilizes the final drives, torsion bars, road wheels, road arms and track from the Bradley infantry fighting vehicle. The upgraded electrical system includes a 70kW generator. A health and usage monitoring system (HUMS) is installed as standard. New in-arm rotary dampers improve performance. The chassis is longer than the original M109 providing greater internal volume. The M109A6 PIM can carry 43 155mm projectiles, including 17 M982 Excalibur precision-guided rounds. The new chassis increases the total weight by about 5% with additional system growth potential built-in. The driver is provided with cameras for improved situational awareness to the front and rear. The existing M109A6 turret is enhanced with a semi-automatic rammer and all-electric drives from the Non-Line-of-Sight Cannon (NLOS-C ). The crew is provided with individual spot cooling as well as standard cooling vests for operations in hot temperatures. The electric gun, ammunition handling components and air-conditioning system are powered by the Common Modular Power System (CMPS). This provides 35kW of 600VDC, which can be used for voltage conversion and can support other power loads required within the complex Paladin platform. The PIM turret rotates 80 deg left or right from center because of the new cabled power system which replaced the slip-ring. The PIM vehicle has a pivot-steer function so that when targets are beyond the traverse limit, the vehicle can slew to that target as fast as the original system could traverse its turret. The A6 PIM vehicle uses Bradley road arm assemblies, torsion bars and idler assemblies and has six roadwheel stations compared to the seven on previous vehicles. New double-pin, double-block 19.1" (485mm) wide XT-161 tracks replace the 14" (356mm) tracks on legacy vehicles. This significantly reduces ground pressure and increases the vehicle's mobility. The existing 155mm/39-caliber M284 gun is retained. A new digital fire-control system is installed and the modular artillery charge system (MACS) will replace bag-type charges. The M109A6 PIM can carry up to 42 conventional 155mm rounds and nine Excalibur rounds. It can fire the Excaliber rounds 25 mi (40 km) and conventional rounds about 19 mi (30 km). The PIM can fire four rounds per minute for three minutes and sustain one round per minute.

M109A7 - 155mm SP Howitzer

NSN TBD

The latest M109 variant designed for the U.S. Army is the M109A7, formerly known as the M109A6 Paladin Integrated Management (PIM). The U.S. Army plans on procuring a fleet of 580 sets of M109A7 howitzers and M992A3 ammunition support vehicles. The first M109A6 and M992A2 vehicles were disassembled and reassembled to M109A7 and M992A3 standard as part of low-rate initial production beginning in summer 2014. Production deliveries began in April 2015.