Ontos, officially the Rifle, Multiple 106 mm, Self-propelled, M50, was an American light armored tracked anti-tank vehicle developed in the 1950s.

It mounted six 106 mm manually loaded M40 recoilless rifles as its main armament, which could be fired in rapid succession against single targets to increase the probability of a kill. Although the actual caliber of the main guns was 105 mm, it was designated 106 mm to prevent confusion with the ammunition for the 105 mm M27 recoilless rifle, which the M40 replaced.

It was produced in limited numbers for the United States Marine Corps after the United States Army cancelled the project. The Marines consistently reported excellent results when they used the Ontos for direct fire support against infantry in numerous battles and operations during the Vietnam War. The American stock of Ontos was largely expended towards the end of the conflict and the Ontos was removed from service in 1969.

Development

The Ontos (Greek for "thing") project was created to be an air transportable tank destroyer capable of being lifted by the cargo aircraft of the 1950s. This limited the vehicle to a weight between 10 and 20 metric tons. The Ontos also had to use the six-cylinder engine then widely used in the Army's GMC trucks. After a number of design and engineering meetings from March through October 1951, manufacturer Allis-Chalmers was awarded an initial contract to produce 14 pilot vehicles, encompassing 6 variants.

Allis-Chalmers' first vehicle, completed in 1952, was based on the running gear of the M56 Scorpion light anti-tank vehicle. The vehicle mounted a cast steel turret with two arms holding three rifles each. This early model could traverse the turret only about 15 degrees. A second prototype used a new suspension system, new tracks, and a newer turret with about 40 degrees traverse. The vehicle could carry only eighteen rounds for the main guns inside the vehicle due to limited space. Its most prominent armament was its six M40 recoilless rifles. Four of the recoilless rifles also had .50 BAT (12.7x77mm) M8C spotting rifles attached, Although the Army had canceled its order, the Marine Corps was desperate for any anti-tank vehicles it could get, and ordered 297. There were also some projects to modernize the M50 with anti-tank missiles.

Service

While the M50 was designed as a tank destroyer, during the Vietnam War most M50s did not engage enemy armor as the North Vietnamese Army deployed few tanks. The Ontos was therefore more widely used by the US Marines for direct fire support for the infantry in combat, a role that was never emphasized in training or doctrine. Its light armor was effective against small arms but vulnerable to mines and rocket-propelled grenades. Consequently, many Ontos were deployed in static defense positions.

The relatively light weight of the M50 made it exceptionally mobile for the amount of firepower it carried. In one operation, the Ontos was the only tracked vehicle light enough to cross a pontoon bridge. In the Battle of Huế, Colonel Stanley S. Hughes felt the Ontos was the most effective of all Marine supporting arms. At ranges of , its recoilless rifles could knock holes in or completely knock down walls. The appearance of an Ontos was sometimes enough to make the enemy break and run, and anecdotal accounts describe the enemy fleeing occupied buildings when an Ontos's spotting round entered a window. In Operation Desoto, the introduction of the large CH-53 Sea Stallion helicopter made possible moving a platoon south of Quảng Ngãi City carrying Ontos in slings underneath the aircraft.

The Ontos was taken out of frontline service in 1969, and by 1970 were removed entirely from service.

Preserved vehicles on display

thumb|right|M50 Ontos at the [[U.S. Army Armor & Cavalry Collection, Fort Benning (now Fort Moore), Georgia, in 2023]]

Of the 297 built, only 14 remain, many of which are the M50A1 model.

  • Russell Military Museum in Zion, Illinois.
  • The Museum of the American GI in College Station, Texas has one undergoing restoration.
  • Indiana Military Museum, Vincennes, Indiana.

See also

  • List of artillery
  • List of self-propelled anti-tank guns
  • List of artillery of the United States
  • G-numbers (SNL G288)

; Similar vehicles

  • Type 60 self-propelled 106 mm recoilless rifle

References

Sources

  • Crismon, Fred (1992). U.S. Military Tracked Vehicles
  • "
  • Digger History page on the Ontos
  • Ontos Anti-Tank Vehicle by Peter Brush