M107 Self-Propelled Gun

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A U.S. Army M107 self-propelled howitzer.

The M107 175mm self-propelled gun was part of a family of self-propelled artillery that also included the M110,the M110E2 chassis had a Depot Level upgraded chassis, drive train due to the heavier “tube” (E2 barrel). The 175 mm gun was used primarily to attack enemy Command, Control and Communication (C3) and Supply Trains, where its 21 mile performance outranged any common Soviet produced weapon. The M110 operated separately from the M107, with about half the effective range (even with Rocket Assisted Projectiles, RAP) but nuclear capable requiring different security, personnel in the Nuclear Personnel Reliability Program (PRP) and nuclear ammunition assembly training (N5). The M107 was the last Self Propelled “Gun” (high velocity, low trajectory, long range) in the U.S. Army inventory. The M110 was a “Howitzer” (low velocity, high trajectory, short range). Both weapons have since been replaced by 155 mm weapons like the M109, due to the fall of the Soviet Union and a change of Strategy, Tactics, (no more massive enemy tank and artillery units) and the types of conflicts/wars the United States faces (High Intensity, Guerrilla Warfare, requiring Artillery surgical strikes, not massive destruction)..

The retube from 175mm to 8 inch (short tube or long tube) had to be done above the organizational (field) level of maintenance, since the chassis also had to be upgraded. The lowest level of retube was done at the Battalion Maintenance using an overhead rail crane/winch. Retube normally occurred at Ordnance Depot Support Units. Or Depot Level, Anniston, Picatiny, Miesau. The M578 Recovery Vehicle was only used to lift the “powerpack” (engine) or final drives (transmission) from the hull, this was done once a month to clean the rubbish from the engine and transmission compartment covered by two aluminum deck plates. The barrels could not be replaced using the M578 due to weight and the precise placement of the barrel (tube) into the cradle without damaging the barrel brass runners. The “retubing” from 175mm to 8 inch was usually accomplished by the Supporting Ordnance Company and required an overhead electric rail winch and chassis modifications for the E2 Barrel. The M578 used the same chassis and drive train components as the M107 and M110.

Both the M107 and M110 are based on a common chassis, It features five road wheels on either side of the chassis with idler arms attached to torsion bars, with the track driven from the front by a 450 hp General Motors turbo supercharged diesel, the turbo charger being connected to the supercharger by a steel pencil size “quill” shaft. The engine and transmission mounted in the front right with the driver to its left. The engine had an attached hydraulic pump that was used to traverse the turret with a manual backup hand crank. The hydraulic pump was sometimes mistakenly used improperly to dig in the rear spade resulting in damage to the hydraulic spade cylinders after the first round is fired. The manual backup was used to Lay the Gun since the hydraulic control was too course. The primary purpose of the hydraulic pump was putting the barrel into battery, ramming ammunition and charges, raising or lowering the rear spade, rapid course deflection adjustment by the gunner, rapid course elevation adjustments by the assistant gunner.

The M107 was deployed during REFORGER Exercises as General Support to the 7th Corps to the front lines to hit way behind enemy lines. Only two rounds are carried with the gun tractor, along with five of the crew of thirteen. Two rounds are fired by the onboard crew of five (Section Chief, Driver, Gunner, Assistant Gunner, Number One (loads primer, hooks up lanyard “pig tail”, pulls lanyard on command)) and the Gun Section moves to avoid counter battery fires and destruction, similar to Sniper Tactics. The rest of the ammunition and crew followed in the M548 Ammunition Carrier based on the M113 chassis and reloads the M107 at a different location from where the Fire Mission occurred. M107 and M110 use the same drive train components as the M578 Recovery Vehicle, and this vehicle has seen wide use in a variety of engineering roles. Early barrels were limited to 300 firings with the maximum Zone 3 propellant, but later examples extended this to between 700 and 1,200 firings with extensive bore scoping by the supporting Ordnance Company.

The M107's combat experience with the US military was almost entirely limited to the Vietnam War. There it proved its effectiveness by having one of the longest ranges of any fielded mobile artillery piece in the Cold war, able to launch a 174 lb projectile out to 21 miles, at 0 deflection and 800 mil elevation. This range advantage, along with the ability to rapidly move from its last position, made it an effective weapon for destroying enemy Command, Control, and Communication and supply trains behind the enemy lines while evading counter-battery fire against even the longest-range Soviet counterparts.

The top speed on the speedometer that I recorded as a M107 driver was 50 mph at Graffenwohr Training Area, Germany on a tank trail. During REFORGER our Battery outran Canadian Armor Units, MBTs (Main Battle Tanks). In practiced Direct Fire during REFORGER two M107 Gun Sections destroyed one Tank Platoon. This is due to the faster reload time, since the M107 has a larger open working space and not the cramped closed space of a tank or M109. In live Direct Fire at ranges exceeding the 120mm Tank Guns the M107 could pick off a Tank Company in column formation and move before the Tanks could get within range. The obsolete tanks used at the Graffenwohr range as targets would get flipped by the near misses. Practiced point of aim was below the front of the target (lead tank). Point of Aim was Point of Impact due to the high velocity of a Gun instead of a Howitzer. Due to the size of the Graffenwohr Range (normally used for tank gunnery) we could only use a maximum of Zone 2, even with Zone 2, multiple target tanks would get flipped by near misses. Our direct fire training was halted due to complaints of the Range Managers, their targets were either completely destroyed or had to be flipped upright and repositioned, essentially closing the Range until this could be done.

Laying the gun involved skilled minute movements of the entire “piece” and not just traversing the turret. The driver, gunner and Section Chief would communicate with each other, with the gunner using hand signals to the driver looking in the left rear view mirror to move the vehicle left or right by tapping on the steering bar. And the other canoneers setting the collimeter and aiming stacks.

The large scale deployment of Lance Missile Batteries assumed the mission of the M107.

The M107 was also frequently used by Israel in the various Arab-Israeli conflicts. When these guns were outranged by rocket fire from Tyre, they were upgraded with the addition of Extended Range, Full Bore ammunition and new powder supplied by Gerald Bull's Space Research Corp, allowing operations over 50 km with increased accuracy.

The M107 was retired from the US Army in the late 1970's but it continues to see use in many armies around the world.