M109 howitzer

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Developed by the U.S. Army, the M109 Paladin is a series of self-propelled 155mm howitzers used by the U.S. and many other nations. The latest version in U.S. service is the M109A6,[1] although a M109A6-PIM is a redesigned version. [2] The evolutionary direction of M109 systems is to make them more and more networked into a common battlefield information system , yet be able to act autonomously. One strong trend, given the real-world ability of a sophisticated enemy to track the trajectory of a shell back to the weapon that fired it, is to be able to "scoot-shoot-scoot": arrive at a location and quickly calculate a trajectory to the target, fire at that target, and then immediately move to a new location before counterfire can strike; the time between stopping, firing, and being ready to move again takes under 60 seconds.[3] Onboard systems linked, by secure voice and data, compute the firing data, automatically unlock the cannon from the travel lock, point the cannon and fire, relock the cannon, and make ready for movement. At any stopping point, either a firing location or an intermediate stop, the M109A6 can be reloaded from its accompanying M992 FAASV) Field Artillery Ammunition Support Vehicle.

It has been scheduled for replacement twice, first by the Crusader, a heavy vehicle that was canceled. The more recent successor has been the Future Combat Systems#NLOS cannon in the Future Combat Systems (FCS), but, in April 2009, Secretary of Defense Robert Gates indicated that there will be major reductions in the FCS program, in the budget to be submitted to Congress.

Individual firing vehicle description


Fire control

The AFCS (Automatic Fire Control System)provides position location and directional reference, a ballistic computer for on-board technical fire direction, a muzzle velocity (MV) measuring system, and gun-drive servos, which automatically orient the tube for deflection and quadrant. It has an embedded training feature, which allows the crew to practice mission scenarios.[1] AFCS subsystems include:

  • AFCS computer unit (ACU) (includes ballistic computation, weapons control, and communications processing circuit cards).
  • Display unit (DU).
  • Hydraulic components (manifolds, servo valves, solenoid valve, and pilot check valves).
  • System interconnect cabling (MIL-STD-1553 data bus).
  • Power conditioner unit (PCU).

Navigation system

A modular azimuth positioning system (MAPS) is made up of modular components combined in different configurations to provide survey and orientation information needs of a particular system. In the Paladin application, major components of MAPS consist of the dynamic reference unit-hybrid (DRU-H), vehicle motion sensor (VMS), and the global positioning system (GPS)/precision lightweight GPS receiver (PLGR).


The DRU-H is mounted on the right trunnion of the Paladin armament system. Operating in conjunction with PLGR, the DRU-H contains all necessary sensor electronics, processing, and input-output circuitry to perform survey and orientation functions and interface with other MAPS components. The DRU-H performs the following functions:

  • Provides vehicle position from a known starting point in terms of universal transverse mercator coordinates of easting, northing, and altitude.
  • Provides vehicle orientation in terms of azimuth from grid north.
  • Compensates for weapon pitch and cant.
  • Supplies angular velocity rates.
  • Provides weapon elevation, grid azimuth, azimuth rate, elevation rate, travel local grid azimuth reference, and travel local elevation reference.

The VMS converts the mechanical odometer to electrical inputs compatible with the navigation system.


The M117/M117A2 panoramic telescope, M145/M145A1 telescope mount, and the M1A1 collimator remain on board the howitzer as backup optical fire control instrumentation.


AN/VIC-1 Intercom, AN/VRC-89 and SINCGARS (single channel ground and airborne radio) subsystem.

Tactical firing units

M109A6 battalions are assigned both to Heavy Brigade Combat Teams (HBCT) and to Fires Brigades. A battalion consists of headquarters, headquarters and service (HHS) battery and three firing batteries.[1]

Each Force XXI Paladin firing battery consists of a battery headquarters, two firing platoons (each with three firing sections) and a support platoon. In the Force XXI battery, a battery operations center (BOC) with FDC takes the place of the two POC elements. The support platoon is comprised of a platoon headquarters, two ammunition sections, a supply section, maintenance section and a food service section. Elements of the support platoon may be consolidated at the battalion level under the HHS, or remain decentralized at battery level.


In addition to conventional warheads such as the high explosive blast/fragmentation M107 unguided shell, the M109A6 can fire the extended-range XM92 Excalibur guided shell from Raytheon and Bofors Defense of Sweden, a BaE Systems subsidiary).

Complementing the projectile warhead is the Modular Artillery Charge System (MACS).

Supporting vehicles and units

Earlier generations, alternatives, and future directions

The system has gone through a series of incremental improvements, many of which were depot-fitted to existing models.[4]

Earlier variants

  • M109: was the first model, with a very short barrel, double baffle muzzle brake, large fume extractor, and a maximum range of 14,600m.
  • M109A1: Longer barrel increasing the range to 18,100m.
  • M109A2: Long tube cannon and mount, with a bustle to provide additional ammunition storage, and aan all-weather ballistic shield over the panoramic telescope. There are maintainability improvements, such as a travel lock and a built-in mount for the alignment device.is a new production weapon which incorporated 27 mid-life improvements to the M109A1. The improvements provide for increased Reliability, Availability, and Maintainability(RAM) and safety characteristics as well as enhanced operational capabilities.
  • M109A3: M109A1 converted to M109A2 improvements
  • M109A4: a M109A2/A3 with Nuclear, Biological, and Chemical/ Reliability, Availability, and Maintainability (NBC/RAM) improvements. While the electrical alternator was upgraded to meet increased needs, the turret traversing mechanism was changed from electric to hydraulic drive.
  • M109A5: a M109A4 with a new M284 cannon and a new M182 gun mount. These improvements provide the M109A5 with greater range and allow for sustained fire for prolonged periods of time.

Crusader project

M109A6 PIM

Reflecting the needs of the Heavy Brigade Combat Teams, the M109A6 Paladin Integrated Management (PIM) program improves readiness and sustainment, including improvements in the M992 Field Artillery Ammunition Support Vehicle.[2]{ Major changes come from systems proven in other vehicles of the HBCT, improving parts interchange and leveraging skills learned on other vehicles. While the PIM version continues to use the main armament and cab, some chassis components are replaced with parts from the M2 Bradley.

In addition, it is an early adopter of features from new development, such as the Future Combat Systems XM1203 NLOS cannon. These include an automated projectile loader, and changing back to modernized electric drives from the hydraulic subsystem introduced in the M109A4. New electric power generation comes from the BAE Systems' Common Modular Power System (CMPS).

General characteristics


  • Combat Weight 63,600lbs
  • Length: 384in
  • Width: 124in
  • Height: 127.4in

Movement capabilities

  • Ground Clearance: 18in
  • Ground Pressure: 113.53psi
  • Fuel Capacity: 133gal
  • Speed: 40mph
  • Vehicle Range: 214 miles

Power train

  • Engine: DDEC 8V71T, 2-cycle diesel, 440hp
  • Transmission: 4 forward, 2 reverse
  • Suspension: Torsion bar high-strength with high-capacity shock absorbers

Electrical and electronics

  • Electrical Power: 650A , 24V DC
  • Travel Clock
  • Inertial positioning navigation system with integral AFCS
  • Night vision compatible


  • Mean Time Between Failure: 122 hours
  • Mean Time to Repair: 2 hours


  • Cannon Range Unassisted: 24km
  • Cannon Range Assisted: 30km
  • Projectile Loading: Semi-automatic
  • Ammunition Capacity: 39 complete rounds, with protected reloading from FAASV
  • Firing Response Time: <60 seconds
  • Sustained Rate of Fire: 1 round/3 minutes
  • Maximum Rate of Fire: 3 rounds/15 seconds; 8 rounds/minute


  1. 1.0 1.1 1.2 , Chapter 1: Mission, Organization, and System Description, FM 3-09.70 Tactics, Techniques, and Procedures for M109A6 Howitzer (Paladin) Operations, 1 August 2000
  2. 2.0 2.1 BAE Systems (Oct 9, 2007), BAE Systems to Unveil Redesigned M109A6 Paladin Self Propelled Howitzer
  3. "Paladin 155mm Self-Propelled Howitzer, USA", Army Technology
  4. M109 155mm SP Howitzer, Federation of American Scientists