M107 self-propelled gun

The M107 175 mm self-propelled gun was used by the U.S. Army from the early 1960s through to the late 1970s. It was part of a family of self-propelled artillery that also included the M110. It was intended to provide long-range fire support in an air-transportable system. It was exported to several other countries including Germany, South Korea, Spain, Greece, Iran, Israel, Italy, the Netherlands, the United Kingdom, and Turkey. The M107's combat history in U.S. service was limited to the Vietnam War; it also saw extensive combat use in Israeli service. The M107 was the last self-propelled gun (high velocity, low trajectory, long range) in the U.S. Army inventory. It shared many components with, and in many cases was replaced by, later versions of the M110. Although withdrawn from U.S. service in the late 1970s, it continues in service with some armies as of 2010.

Design and Production History
During the 1950s, the standard of US Army motorized 203mm artillery was the M55, based on the chassis and the turret of the M53 155mm Self-Propelled Gun, which used some components from the M48 tank. The weight of the M55, at 44 metric tons, prohibited air transportation and its gasoline engines limited its range to approximately 260 km, as well as presenting an explosion hazard in combat.

This led the U.S. Army to issue a requirement for a new series of self-propelled artillery: lighter, so as to be transportable by air, while continuing the practice of deriving several vehicles from the same chassis, which simplified maintenance and training. The Pacific Car and Foundry (Paccar) company developed several prototypes. The 175 mm T235 self-propelled gun and 203 mm T236 self-propelled howitzer were driven by a diesel engine and, aside from the different armament, were essentially the same vehicle. They were introduced into U.S. Army service as the M107 and M110 in 1962 and 1963, respectively.

Paccar received the M107 and M110 design contracts and initial manufacturing single source bid from Detroit Arsenal. This was based on patented key features of the M55: the gas equalibrator [2911209] balance of the barrel that hydraulically trimmed with terrain fall line sensing pendulum [2857815], no back pawl limits on aiming, parabolic taper hydraulic recoil cylinders [not patentable], and hydraulic lock out of suspension when shooting [3117800]. Two other firms also produced the M107: FMC, between 1965 and 1980, and Bowen-McLaughlin-York.

Both the M107 and M110 use the same drive train components as the M578 Light Recovery Vehicle. In addition to its use in performing maintenance on the M107 and M110, and for recovery of damaged or inoperable vehicles, this vehicle has seen wide use in a variety of engineering roles.

Many of the M107s were rebuilt into the M110A2 configuration.

Chassis
Both the M107 and M110 are based on a common chassis, which features five road wheels on either side of the chassis, idler arms attached to torsion bars, tracks driven from the front by a 450 hp General Motors turbo supercharged diesel with the turbocharger connected to the supercharger by a steel pencil sized “quill” shaft. The engine and transmission are mounted in the front right, with the driver to its left. The engine had an attached hydraulic pump used to traverse the turret with a manual backup hand crank.

The hydraulic pump was sometimes improperly used to dig in the rear spade, resulting in damage to the hydraulic spade cylinders after the first round was fired. The manual backup was used to lay the gun, since the hydraulic control was too coarse. 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 and rapid course elevation adjustments by the assistant gunner.

Key recognition features

 * Long thin barrel without a fume extractor or muzzle brake.
 * Gun is in an unprotected mount towards the rear of the hull with a large spade at the rear that is raised for traveling.
 * Chassis is same as M110 203 mm self-propelled howitzer with five large road wheels on each side, a drive sprocket front wheel and has no track-return rollers.

Performance
The top speed recorded by one M107 driver was 50 mph at the Grafenwöhr Training Area, Germany, on a tank trail. This speed was also achieved in an M107 by the U.S. Army's Vilseck Maintenance Facility after replacing a broken torsion bar.

Operations and maintenance
The M107 has a larger open working space than the closed space of tank-like self-propelled artillery such as the M109 howitzer. This allows for faster reload times and its high maneuvering speed and fast reload time allows the M107 to practice shoot-and-scoot, redeploying before the firing position can be zeroed in on.

One drawback of the M107 in combat was that laying the gun involves skilled minute movements of the entire vehicle. The gunner uses hand signals to the driver, who views them in the left rear view mirror and moves the vehicle left or right by tapping on the steering bar. The other cannoneers set the collimeter and aiming stakes under the direction of the gunner.

Only two rounds are carried with its gun tractor on "loading trays". These rounds can be fired by the onboard crew of five (Section Chief, Driver, Gunner, Assistant Gunner, Number One Cannoneer) of the crew of thirteen. The rest of the ammunition and crew follow in the M548 Ammunition Carrier. If the gun was facing hostile artillery, the gun would fire and relocate where these crewmen would reload the M107 at the new location to avoid counter-battery fire.

Each member of the M107 crew has specific duties when the vehicle is firing:

The section chief operates the hydraulic load and ram, verification with "gunner's quadrant", as well as operating the rear spade and left spade unlock. The driver operates the positions spade and the barrel travel lock. The gunner controls deflection (the horizontal direction in which the gun is pointing). The assistant gunner controls elevation. The number one cannoneer opens and closes the breech, verifies ramming of the round with ram rod and powder load red on the rag (which means he can see the red igniter patch to verify that the powder is not put in backwards), loads the primer, hooks up the lanyard (pig tail), pulls lanyard on command, and unlocks the right spade lock. Cannoneers two through nine set up the collimeter, aiming stakes, bore sight (in direct fire missions only), communications, prepare additional ammunition (including fuzing) and powder zones, provide security, drive the M548, operate the ring-mounted M2 .50 caliber machine gun, set up camouflage nets, dig a burn pit, and conduct the resupply of ammunition.

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.

Retubing the barrel was necessary when the barrel had exhausted its service life or when converting the M107 to an M110. In U.S. Army service, the lowest level of retube was done at the artillery battalion's maintenance shop. Retubing could also be done by Ordnance Depot Support Units or at fixed depots such as Anniston Army Depot, Picatinny Arsenal, or the Miesau Army Depot in Germany. When retubing was done at the battalion level, the M578 Light Recovery Vehicle was used. The barrels could not be replaced using a single M578 due to weight and the need for precise placement of the barrel into the cradle to prevent damaging the barrel brass runners. Two cranes were used – one on either end of the barrel. A single M578 was used to lift the engine or transmission from the hull once a month to clean the engine and transmission compartment, which was covered by two aluminum deck plates. Retubing could also be used to convert the 175 mm M107 to the 203 mm (8 inch) M110. This retubing was usually accomplished by the supporting ordnance company or a fixed depot as it requires an overhead electric rail winch and chassis modifications for the E2 barrel.

Combat history


The M107's combat experience with the U.S. military was almost entirely limited to the Vietnam War. There it proved its effectiveness by having one of the longest ranges of any mobile artillery piece operated during the Cold War. The M107 was able to launch a 147 lb (67 kg) projectile out to 21 miles (34 km), at 0 deflection and 800 mil (45°) elevation. This range advantage, along with the ability to rapidly move from its last position, made it an effective weapon for destroying North Vietnamese Army and Viet Cong command, control, communications facilities and supply trains, while evading counter-battery fire from the longest-range Soviet counterparts. This was proven in 1968 at Khe Sanh.

The M107 also had disadvantages. It was noted for its inaccuracy at longer ranges. The gun was assigned to corps artillery units and a number of M107/M110 composite units were formed allowing the option of responding with the longer range M107 or the more accurate M110. In addition, as noted above, the tube on the M107 required frequent changing on early versions. Individual batteries did not have the necessary support equipment for changing the tube, so higher-level maintenance support was required.

The M107 was also used by the Israel Defense Forces in the various Arab–Israeli conflicts from the Yom Kippur War on. During the Yom Kippur War it was one of the few weapons able to destroy Egyptian and Syrian anti-aircraft missile positions. Of the 15 SA-2 batteris lost by Egypt on the east bank of the Suez Canal, 13 were destroyed by M107's. When the IDF crossed the Suez Canal in Operation Gazelle, M107 SP guns were among the first to cross together with tanks and APC's. 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 Corporation. This allowed operations over 50 km with increased accuracy. The IDF acquired up to 175 vehicles. In IDF service, the M107 is known as the Romach (spear or lance).

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

Users

 * 🇩🇪 West Germany
 * 🇬🇷 Greece: Hellenic Army 36, 24 converted to M-110A2
 * 🇮🇷 Iran: Islamic Republic of Iran Army.
 * 🇮🇱 Israel: Israel Defense Forces.
 * 🇮🇹 Italy
 * 🇰🇷 South Korea: Republic of Korea Army. 24, out of service since 2008.
 * 🇹🇷 Turkey: Turkish Army.
 * 🇪🇸: Spanish Army. 12, converted to M110A2 in the early 1990s.
 * 🇺🇸 United States: United States Army and United States Marine Corps.
 * 🇬🇧 United Kingdom: Royal Artillery.