By Matthew J. Seelinger
Since its large-scale adoption by armies in Europe during the Early Modern Era, artillery—particularly field artillery—has often played a decisive role on the battlefield. Military leaders such as Gustavus Adolphus of Sweden and Napoleon Bonaparte of France introduced technical innovations and tactics that improved field artillery and increased its effectiveness on the battlefields of Europe and elsewhere.
In the U.S. Army, field artillery made great strides during the nineteenth century and proved decisive in many battles during the Mexican War and the Civil War. While the Army’s Field Artillery branch could not match the firepower of the European powers during World War I, by World War II, U.S. field artillery often dominated the battlefield in its campaigns in North Africa, Europe, and the Pacific. During the Korean War, massive use of artillery, employing large stockpiles of ammunition left over from World War II, offset the advantage in manpower by Communist forces.
Field artillery would continue to play an important role in Vietnam. Emplaced at dozens of fire support bases (FSBs) across South Vietnam, U.S. Army artillery, including 105mm, 155mm, and 8-inch howitzers, along with 175mm guns, provided crucial support to infantry in the field or other FSBs under enemy attack. American guns also engaged in long-range duals with enemy artillery in North Vietnam and Laos. While some of the artillery systems were essentially the same ones used in World War II and Korea, the M102 105mm howitzer was an artillery piece introduced during the Vietnam War, and it was intended to replace the older, heavier, and more limited M101A1 105mm howitzer.
The M2 105mm howitzer, later designated the M2A1 with the addition of an improved carriage, was the Army’s primary light artillery piece in World War II. Developed during the 1920s but not fully introduced into Army field artillery units until the eve of World War II, the M2 replaced the obsolete M1897A4 75mm gun, a U.S.-built version of the famed “French 75.” A heavy, durable weapon weighing in at 4,980 pounds, the M2A1 had a barrel length of 7 feet, 7 inches (2.31 meters), and an overall length of 19 feet, 6 inches (5.9 meters), with its split trail locked for travel. The M2A1’s barrel could be depressed -5 degrees (80 mils), elevated 65 degrees (1,156 mils), and traversed 23 degrees (409 mils) right or left, and it could fire a variety of semi-fixed ammunition (high explosive, smoke, chemical) to a maximum range of 11,270 meters (7 miles).
By the time production ended in 1953, Rock Island Arsenal in Illinois had produced 10,200 M2A1s, and they saw extensive action in World War II and the Korean War with Army and Marine Corps field artillery units as well as the armies of several Allied nations. The M2A1, redesignated the M101A1 in 1962, remained the Army’s main light artillery system heading into the Vietnam War.
With the Army’s emphasis on airborne and airmobility operations after the Korean War, and especially with the introduction of improved rotary-wing aircraft such as the UH-1 Iroquois (or “Huey”) and CH-47 Chinook, Ordnance Corps and Field Artillery officials began looking at designs for lighter weapons more easily transported by air. Work on new designs began in earnest in 1962. By the time large numbers of combat troops began deploying to Vietnam in 1965, the Army had developed the XM102 lightweight 105mm howitzer at Rock Island Arsenal.
Using aluminum alloys and other lightweight materials in the construction of the XM102, particularly in the weapon’s carriage and trail, allowed for a significant reduction in weight—3,298 pounds versus 4,980 for the M101A1. As a result, the M102 could be airlifted by a CH-47 helicopter with a larger supply of ammunition than the heavier M101A1. For ground transport, M102 could be towed by a ¾-ton truck (and later by an M998 Humvee), while the heavier M101A1 required a larger 2 ¼-ton truck. The M102’s longer barrel, measuring 11 feet, gave it a better range—11,500 meters (7.1 miles), with a maximum range of 15,100 meters (9.4 miles) firing a rocket-assisted projectile. The usual rate of fire for the M102 was three rounds per minute (RPM), with a maximum of ten RPM.
Unlike the M101A1, which had a traditional split-trail carriage, the M102 used an innovative box carriage. What truly gave the M102 an advantage over the older M101A1 was its ability to be quickly traversed a full 360 degrees (6,400 mils) by a single soldier. The M101A1 had a limited on-carriage traverse that required its trails (stabilizing legs) to be dug up and shifted by the gun crew if further traverse was necessary—a time-consuming and laborious process. To prepare the M102 for firing, the crew lowered a circular base plate carried under the trail and staked it to the ground before the wheels were raised clear off the ground. At the rear of the trail a longitudinal roller fitted with a “Terra-Tire” replaced the traditional spades found on the trails of the M101A1 and allowed the gun to be quickly traversed in any direction. Both howitzers used a similar hydro-pneumatic recoil system, with the M102 having two exposed spring equilibrators, one each per side of the gun. Early models of the new howitzer featured a muzzle brake, and several howitzers so equipped saw service in Vietnam, but it was later eliminated on the M102.
While the M102 had advantages over the M101A1, it took some effort to convince seasoned artillerymen that the new gun was better. According to an Army Vietnam study, Field Artillery, 1954-1973, many redlegs knew every detail of the older weapon and were convinced it would never let them down in combat. Since the M102 was lower to the ground, the breech was lower, making it harder to load (the M101A1’s breech was waist-high). The M101A1 also had higher ground clearance when in tow. Despite their arguments, the M102 simply possessed too many advantages to prevent the Army from adopting it to replace its older artillery piece.
The Army began deploying M102s in 1966, and replacement of the older howitzer continued over the next four years. The first unit to receive M102s was 1st Battalion, 21st Artillery, 3d Brigade, 1st Cavalry Division (Airmobile). In addition to firing high explosive, smoke, and white phosphorous rounds, the M102 fired a new type introduced during the Vietnam War, the M546 antipersonnel round, first used in 1966. The M546 was direct-fired from a near-horizontal elevation, and it ejected 8,000 small darts, or flechettes. Known as the “Beehive” round for the way the flechettes were stacked in the shell, but also for the buzzing noise the flechettes made in flight, the M546 was effective against masses of attacking enemy infantry.
By the time production ended in the early 1970s, the Army had acquired some 1,150 M102s. Hundreds more were exported to over a dozen countries, largely in Latin America and Asia. Several examples were captured by Communist forces during the final offensive that led to the fall of South Vietnam in the spring of 1975.
The M102 was later used in combat in Grenada in Operation URGENT FURY in 1983, in Panama during Operation JUST CAUSE in 1989, and in Iraq during the Persian Gulf War in 1991. In each operation, M102s were employed by airborne, air assault, or light infantry units. In 1989, the Army began replacing the M102 with the M119 105mm howitzer, a gun based on a British design built under license, in Regular Army field artillery units while National Guard battalions retained their M102s. The M102 last saw combat with the Army in 2004 in Iraq while serving with 1st Battalion, 206th Field Artillery (1-206 FA), 39th Infantry Brigade Combat Team, of the Arkansas Army National Guard. During 1-206 FA’s deployment, it was reported that National Guard gun crews scavenged spare parts from M102s of the Iraqi Army, and that these examples had been captured from Iran during the Iran-Iraq War of 1980-88.
While Army and Army National Guard field artillery units no longer use the M102, the U.S. Air Force continues to equip its AC-130 gunships with it. M102-eqipped AC-130s were first used in the latter part of the Vietnam War, and the gun proved extremely effective against enemy ground targets. Later M102-eqipped variants of the AC-130 saw action in Operations URGENT FURY, JUST CAUSE, DESERT STORM, RESTORE HOPE, ALLIED FORCE, ENDURING FREEDOM, and IRAQI FREEDOM. The most recent variant of the AC-130, the AC-130J Ghostrider, was originally designed without the venerable M102, but in early 2015, at the request of Lieutenant General Bradley Heithold, the commander of U.S. Air Force Special Operations Command, the M102 was included as part of the Ghostrider’s armament.
A handful of M102s remain in service with armies around the world, some of which are used solely as salute guns for ceremonies. Several examples are on display in the United States at veterans’ memorials or military museums, including the U.S. Army Artillery Museum at Fort Sill, Oklahoma, the home of the U.S. Army Field Artillery branch. There, visitors can see an M102 as part of the museum’s impressive exhibit on artillery of the Vietnam War.
