M50 Ontos

The Ontos (Greek for "thing"[1]) 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. Allis-Chalmers was awarded a contract on August 12, 1955, for 297 vehicles.

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. Four of the recoilless rifles also had .50 BAT (12.7x77mm) M8C spotting rifles attached, each of which fired a tracer round with the same trajectory as the 106 mm round, and that gave off a flash and puff of white smoke on impact. The spotting rifles were used to line up the 105 mm recoilless rifles with the target. The Ontos also carried a single .30 caliber (7.62 mm) M1919A4 machine gun for anti-infantry use.

The vehicle was taken to the Aberdeen Proving Ground where single rifles had been tested earlier. When all six weapons were fired at once, the back blast from the firing knocked bricks out of a nearby building and knocked the rear windows out of several cars. The prototype and testing stage was completed by 1955, at which point the Army canceled its order.

As an anti-tank vehicle the Ontos had several problems, including a small ammunition load, a very high profile for such a small vehicle, and the need for the crew to exit the vehicle in order to reload the guns, exposing them to enemy fire. Although the Army canceled their order, the Marine Corps were desperate for any anti-tank vehicles they could get, and ordered 297. Production ran from 1955 through 1957. The Marine Corps accepted its first vehicle on 31 October 1956.

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 300 to 500 yards (270 to 460 m), 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 25 miles (40 km) south of Quảng Ngãi City carrying Ontos in slings underneath the aircraft.[2]

The Ontos units were deactivated in May 1969, and some of the vehicles were handed over to an Army light infantry brigade. They used them until they ran out of spare parts, and then removed the turrets and used them as fixed fortifications. Both these and the rest of the vehicles returned from Vietnam in 1970 and were cut up for scrap, with some of the chassis being sold off to be converted into construction vehicles. Some of the Ontos that were sold to construction companies were later acquired by collectors for restoration.

The Ontos did see use as an anti-tank weapon during the American involvement in the Dominican Civil War: on 29 April 1965 an M50 Ontos and an M48 Patton of the 6th MEU engaged and destroyed two rebel L/60L light tanks, each destroying one. In another instance, an Ontos destroyed an AMX-13.[3]

There are Ontos on display at the following US locations:

• The Patton Museum of Cavalry & Armor in Fort Knox, Kentucky[4] (no longer on display, may have moved with the Armor school to FT Benning).
• The Rock Island Arsenal Museum in Rock Island, Illinois.
• Camp Atterbury, Edinburgh, Indiana.
• The American Military Museum, in El Monte, California has an M50 that is missing its six recoilless rifles.
  

  An M50A1 Ontos on display at the National Museum of the United States Marine Corps in Quantico, Virginia.
  The Aberdeen Proving Ground's Museum in Aberdeen, Maryland has a T165E2, the 19th prototype, though it is not currently on display. The vehicle is currently undergoing a cosmetic restoration.
• Fred Ropkey, owner of the Ropkey Armor Museum in Crawfordsville, Indiana owns the first prototype T165, a later model Ontos, and a parts machine.
• The National Museum of the Marine Corps in Quantico, Virginia has completed the restoration of an M50A1 Ontos.
• The Museum of The Marine in Jacksonville, North Carolina has an operational M50A1 Ontos which is not on public display.
• There is an M50A1 Ontos on outside display at the Navy Facility at China Lake, California.
• The Marine Corps Air Ground Combat Center Twentynine Palms, California has an M50A1 Ontos on outside display.
• The Military Vehicle Technology Foundation in Portola Valley, California has a T165E1 prototype with the original GM 302ci engine which is currently undergoing a complete operational restoration, and a second prototype T165E2 Ontos.
• The U.S. Army Artillery Museum at Ft. Sill, Oklahoma.
• The Marine Corps Mechanized Museum, Camp Pendleton, displays a M50A1 Ontos that took part in the Battle of Hue.[5]
• There is an M50 Ontos on display inside of the National Museum of Military Vehicles in the Vietnam exhibit, near Dubois, WY[6]
• Russell Military Museum in Zion, IL.
• The Museum of the American GI in College Station, TX has one undergoing restoration.[7]

• 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 Gun

• Estes, Kenneth W (2016). M50 Ontos and M56 Scorpion 1956–70: US Tank Destroyers of the Vietnam War. New Vanguard 240. Osprey Publishing. ISBN 9781472814739.
• Kutta, Timothy J., "ONTOS: The USMC's Most Famous Anti-Tank Weapon", Modern War magazine, Bakersfield, California: Strategy & Tactics Press (Decision Games), no. #14 November/December 2014, pp. 72–75
• McNab, Chris (2003). Military Vehicles. Hoo, Kent, UK: Grange Books. p. 56. ISBN 1-84013-539-5.

Wikimedia Commons has media related to M50 Ontos.

• Digger History page on the Ontos
• Ontos Anti-Tank Vehicle by Peter Brush