The M107 175mm Self-Propelled Gun
by Matthew J. Seelinger
During the Vietnam War, the U.S. Army established artillery firebases around South Vietnam to support American and Army of the Republic of Vietnam (ARVN) infantry operations. Artillery at these firebases was also used to interdict Viet Cong (VC) and North Vietnamese Army (NVA) troop movements and to provide counter-battery fire against enemy rocket positions and artillery batteries. One weapon employed by American and later ARVN artillerymen was the M107 175mm self-propelled gun.
Throughout the Army’s history, artillery, the “King of Battle,” has played an important, often decisive, role on the battlefield. Despite the development of atomic weapons and an increased reliance on rockets and missiles in the early 1950s, the Army still possessed thousands of tube artillery systems, including towed and self-propelled 105mm, 155mm, and 8-inch howitzers and guns. However, the Army’s artillery doctrine began to undergo a transformation that emphasized air-transportability, speed, range, and commonality of parts. As a result, the Army issued a requirement for a new series of lighter, self-propelled artillery systems in 1956. The Pacific Car and Foundry Company (Paccar) of Renton, Washington, was subsequently awarded a contract by the Army’s Detroit Arsenal for design, development, and construction of six prototype systems, including two 175mm self-propelled guns designated the T235, three 8-inch (203mm) self-propelled howitzers designated the T236, and one 155mm self-propelled gun designated the T245.
All three models included the interchangeability of the gun tube on a common mount, as well as on a common chassis. Each system also represented a significant reduction in weight in comparison to previous versions of self-propelled artillery. Tests on the new systems began in late 1958. During the following year, each vehicle was retrofitted with diesel engines to improve range and safety. The Army completed trials with each system in early 1961. In March of that same year, the T235 was standardized as the M107 and the T236 as the M110. The Army ceased further development of the T245.
In June 1961, the Army awarded Paccar the initial production contract for the M107, in addition to the M110. After M107s rolled off the production line in 1962, the Army formed its first M107 battalion at Fort Sill, Oklahoma, in January 1963. Two other companies, FMC of San Jose, California, and Bowen-McLaughlin-York of York, Pennsylvania, were later awarded contracts to manufacture the M107.
The M107 was a powerful weapon system that could out-range any other American or NATO artillery piece when it was introduced. It was operated by a crew of thirteen, five of whom rode on the gun vehicle and rest on the M548 tracked cargo carrier, which carried most of the ammunition and powder (two rounds were carried on the M107). The driver was the only crew member under the cover of armor (maximum of 20mm) and drove the M107 with the aid of three M17 periscopes. With no overhead armor like the M109 155mm self-propelled howitzer, the rest of the crew was vulnerable to counter-battery and small arms fire. However, the lack of an armored turret provided more open working space and allowed for faster reload times. The M107s speed and maneuverability also allowed it to be quickly repositioned to a new firing position before the enemy could zero in on it (“scoot and shoot”).
The M107 weighed in at just over thirty-one tons. Powered by a General Motors 8V71T eight-cylinder supercharged diesel engine, the M107 could reach road speeds of up to fifty miles per hour (eighty kilometers per hour) and had an operational range of 450 miles (725 kilometers). Fully tracked and with a ground clearance of seventeen inches (forty-four centimeters), the M107 was capable of driving across various types of terrain. It did not have an amphibious capability but could ford streams approximately 3 ½ feet (1 meter) deep.
The M107’s length with its gun was 36 feet, 11 inches (11.26 meters); the length of the vehicle alone was 18 feet, 9 inches (5.72 meters). The M107 had a width of 10 feet, 4 inches (3.15 meters), and a height (with the gun in travelling position) of 12 feet, 1 inch (3.68 meters).
The M107’s armament was the M113 175mm gun developed at Watervliet Arsenal in New York. The gun could be elevated sixty-five degrees, depressed minus two degrees, and traversed thirty degrees left or right. Elevation, depression, and traverse were carried out by using the M107’s hydraulic system, but manual controls could be used in an emergency. The M107 was equipped with a hydro-pneumatic recoil system. In addition, mounted at the rear of the vehicle chassis was a large hydraulically operated spade which was positioned prior to firing the gun.
Since the M107 fired a shell weighing in at 147 pounds, the system was equipped with a hydraulically powered loader and rammer that lifted the projectile from the rear of the vehicle and rammed it into the breech. Manual controls were also available for the loader/rammer in case the M107’s hydraulics failed.
The M107 fired only high explosive projectiles, either the M437A1 or M437A2. The shell and propellant were loaded separately. The M107’s gun had a maximum range of approximately twenty miles (thirty-two kilometers). While the M107 had exceptional range, the propellant charge (zone 3) required to fire a shell to maximum distance quickly wore out the barrel. As a result, gun tubes needed to be changed frequently—early versions could wear out in as a few as 300 rounds fired with zone 3 propellant. Later, improved versions could handle up to 1,200 firings before requiring replacement. In addition, the M107 suffered from accuracy problems at long ranges. The usual rate of fire was one round per minute, but a well-trained crew could shoot two rounds per minute for short periods of time.
The Army deployed M107s into battalions of twelve guns at the corps level. Combat service for Army M107s was limited to Vietnam. During the war, the Army deployed ten M107 175mm gun/M110 8-inch howitzer battalions to Southeast Asia. Since the M107 and M110 8-inch self-propelled howitzer shared the same chassis, the Army formed these composite battalions to allow artillery commanders the option of firing the long-range 175mm gun or the heavier, shorter range, but more accurate, 8-inch howitzer, depending on the mission.
While the M107 carried out various types of fire missions in Vietnam, it proved most valuable in northern South Vietnam, supporting the U.S. Marine combat base at Khe Sanh while it was under siege in early 1968, and engaging in long-range artillery duels with North Vietnamese guns across the Demilitarized Zone. The M107’s heavy shell was effective at penetrating the heavy jungle canopy of Southeast Asia and destroying hidden Viet Cong and North Vietnamese Army command, control, communication, and supply facilities. When the United States withdrew from Vietnam in 1973, several M107s were transferred to South Vietnamese forces. Some of those not destroyed during the final offensive by Communist forces in the spring of 1975 can be seen in war museums and memorials across Vietnam.
Several nations allied to the United States acquired the M107 for their armed forces, including the United Kingdom, Iran, Israel, Turkey, Italy, Greece, Spain, the Netherlands, West Germany, and the Republic of Korea. U.S. Marine Corps artillery units were also equipped with the M107. Israel used M107s during its wars with its Arab neighbors. With the help of artillery expert Gerald Bull, the Israeli Defense Forces extended the range of its M107s to thirty miles (fifty kilometers). Iran, which acquired the M107 prior to the overthrow of the Shah, employed its M107s in its bloody war with Iraq in the 1980s.
The overall service life of the M107 proved to be relatively short. By the late 1970s, the Army began to convert its M107s into M110A2s, an improved version of its self-propelled 8-inch howitzer. By 1981, the Army completed the conversion, ending the M107’s eighteen-year service with the U.S. Army. The Marine Corps soon followed the Army’s lead, and many nations that had acquired M107s also converted them to M110A2s or withdrew them from their armed forces.