M107

   The M107 is a long-ranged self-propelled gun manufactured in USA. It was designed based upon requirements that were determined by the US Army in the late 1950s. It was intended to propel heavy projectiles over vast distances, with the intent of attacking strategic targets in the enemy's rear area from the frontline. Examples of such targets include fuel dumps, train stations, airbases, and command centers.

   During the formulation of the requirements that spawned the M107's development, a towed 175-mm gun was also considered by the US Army, but the mobility offered by a self-propelled 175-mm gun was deemed far more important for running artillery missions in Central Europe. Though in an ironic twist of fate, the Soviet Union developed and fielded equivalents to both a towed and self-propelled 175-mm gun - the 180-mm S-23 and 203-mm 2S7 Pion, respectively. Production of the M107 SPG began in 1962, and continued until 1980, with a total of 524 units built.

   The M107 is 11.25 m long overall, 3.15 m wide, 3.47 m tall, and weighs 28.2 tonnes at combat weight. It has a ground clearance of 0.44 m, and can tackle a 60% gradient or a 30% side slope, climb a 1 m vertical step, cross a 2.36 m trench, and ford 1 m of water. With 28.2 tonnes atop an overall track footprint of 34.59 m, the M107 has 0.82kg/cm² of ground pressure.

   The dominant recognition feature of the M107 is it's colossal 175-mm gun, which is thin, extremely long, and has a bull barrel. The gun sits atop a carriage in a slot that allows the tube to recoil rearward. This carriage is attached to a rotating mount at rear of the chassis, while the front of the carriage is attached to a pair of tall, narrow gun carriage cheeks by a pair of long pneumatic struts.

   The chassis itself is largely flat and featureless, with a short and shallow frontal slope, and the driver's hatch at the extreme front-left of the vehicle. The M107 has a flat-track, with no return rollers; instead, the track rests atop the 5 very large roadwheels. The drive sprocket is forward, and there is no return roller. A large, hydraulically deployable spade is fitted to the rear of the M107's chassis, which may also be used as a dozer blade. This spade is dug into the ground before firing the 175-mm gun. It is highly doubtful that the M107 can be fired safely without deploying it.

   The M107 is operated by a crew of 13 men. There is room for 5 crew members on board. The driver sits in the aforementioned position, with the two gunners sitting atop the chassis on the left and right of the weapon mount, and two loaders sitting atop the right side of the weapon mount. The remainder of the crew rode in accompanying M548 tracked cargo carriers or M992 FAASVs, some of which carried additional ammunition and supplies.

   The propulsion of the M107 is a General Motors 8V71T diesel V8 with 345 at 2 300 rpm, coupled to an Allison XTG-411-2A automatic transmission with 4 forward gears and 2 reverse gears, producing a top speed of 56 km/h. The fuel capacity is 1 100 liters, allowing for a 720 km range.

   The only weapon on the M107 is it's M113 gun (not to be confused with the M113 APC), fitted to an M158 mount. The M113 is a rifled bore 175-mm gun (as opposed to a howitzer) with a 60 caliber tube. The complete weapon can elevate to +65 degrees, depress to -2 degrees, and traverse through 60 degrees (up to 30 degrees to either side). It fires 79 kg projectiles at 1 rpm, out to a range of up to 40 km. The muzzle velocity is 914 m/sec. Depending on the type and number of charges used in each shot, and the maintenance applied to the 175-mm M113 gun, it's tube life could span from 700 to 1 200 rounds (early M113 tubes could only withstand 300 full charges).

   Only 2 types of 175-mm ammunition were developed for the M113 gun; the 66.6 kg M437 HE round, and a 79 kg nuclear round with a 15kT yield, both fired using M86 propellant charges. Due to the tremendous size and weight of the ammunition, as well as the propellant charges used to project it, only 2 rounds are carried on the M107 itself. In practice, additional ammunition is carried by support vehicles.

   While the M107 excels in mobility and firepower, it is greatly lacking in protection. The only crew position with any protection (or even cover from the elements) is the driver's station, whose 13 mm thick RHA steel armor (only enough to protect from blasts, shell splinters, and 7.62-mm rifle fire) is itself somewhat lacking. Protection against casualties by NBC weapons requires the crew to don protective clothing, such as the MOPP suit, but no protection is offered to any crewman against any weapons. It goes without saying, but the M107's crew is thus extremely vulnerable to counter-battery fire, snipers, strafing runs, and even the effects of the M107's own nuclear ammunition. Sets of Kevlar shields were issued to M107 batteries in order to lessen thier vulnerability, but the benefits these offered were considered by crews to be poor, in light of the difficulty of carrying, erecting, and removing them. In practice, the Kevlar shields were usually left stowed on the sides of M107s, and were sometimes even thrown away by crews, prior to entering the field.

   Despite it's vulnerability, the M107 had enjoyed an outstanding combat record. In Vietnam, it was the only land-based US artillery piece that outranged the infamous Soviet 130-mm M46 (with a range of 30 km), and the M107 gained fame in the Siege of Khe Sanh for this feat. It was equally successful in the 1973 Yom Kippur War, in which the IDF used M107s to shell targets in Damascus. The M107s operated by Iran also saw extensive combat service, and were used throughout the Iran-Iraq War (alongside 170-mm M1978 Koksans, in the later years of the war).

   Eleven countries have operated the M107; Greece, Iran, Israel, Italy, the Netherlands, South Korea, Spain, Turkey, USA, the UK, and West Germany. As of 2010, the M107 is still used by Iran (200 M107s), Israel (175 M107s), and South Korea (100 M107s). The status of these weapons is uncertain, but they are probably still operable.

   The unit cost of the M107 is approximately $159 000, though it is no longer offered, nor available for new production.

Variants

   M110; this is basically the same chassis, mounting a 203-mm howitzer instead of a 175-mm gun. Because both the M107 and M110 are fully-modular and thier weapons are easily interchangeable, M107s frequently became M110s - and vice-versa - in armies that operated both weapons. All US-operated M107s were converted into M110A2 howitzers by 1981, though the latter has since been phased out of service as well.;

   M578 armored recovery vehicle, also uses the same chassis as the M107;

   Romach - an Israeli variant of the M107, apparently with no significant modifications.

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