| Rifle, Multiple 106 mm, Self-propelled, M50 "Ontos" | |
|---|---|
 Ontos M50A1, the 50-cal spotting rifles can be seen on the upper guns | |
| Type | Tank destroyer |
| Place of origin | United States |
| Service history | |
| In service | 1956–69 |
| Used by | United States |
| Wars | 1958 Lebanon Crisis Dominican Civil War Vietnam War |
| Production history | |
| Designer | Allis-Chalmers |
| Designed | 1952 |
| Manufacturer | Allis-Chalmers |
| Produced | 1955–57 |
| No. built | 297 |
| Variants | M50A1 |
| Specifications | |
| Mass | 8,600 kg (19,000 lb) |
| Length | 3.83 m (12 ft 7 in) |
| Width | 2.59 m (8 ft 6 in) |
| Height | 2.13 m (7 ft 0 in) |
| Crew | 3 (driver, gunner and loader) |
| Sights | x6 .50 Single-Shot Spotting Rifles |
Main armament | 6 ×M40A1C recoilless rifles |
Secondary armament | 1 × .30 (7.62 mm)M1919 Browning machine gun |
| Engine | GM 6-cylinder inline 302 cu in (4.95 L) gasoline engine 145 hp (108 kW) |
Operational range | 185 km (115 mi) |
| Maximum speed | 48 km/h (30 mph) |
Ontos, officially theRifle, Multiple 106 mm, Self-propelled, M50, was an American light armored trackedanti-tank vehicle developed in the 1950s.
It mounted six 106 mm manually loadedM40 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 M50 replaced.
It was produced in limited numbers for theUnited States Marine Corps after theUnited 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 theVietnam War. The American stock of Ontos was largely expended towards the end of the conflict and the Ontos was removed from service in 1969.
TheOntos (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 20metric 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, manufacturerAllis-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 theM56 Scorpion light anti-tank vehicle. The vehicle mounted a cast steelturret 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 sixM40 recoilless rifles. Four of the recoilless rifles also had .50 BAT (12.7x77mm) M8C spotting rifles attached,[2] each of which fired a tracer round with the sametrajectory as the 105 mm round, and which 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.[2]
The vehicle was taken to theAberdeen 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.[3] Although the Army had canceled its order, theMarine Corps was desperate for any anti-tank vehicles it could get, and ordered 297.[3] Production ran from 1955 through 1957. The Marine Corps accepted its first vehicle on 31 October 1956.
Several variants were also studied. TheUtility Vehicle, Tracked, Infantry, T55 was a lightArmored personnel carrier (APC), but only two versions of the prototype were built. It proved impractical due to the limited room inside, carrying only five infantry and forcing the driver to lie prone. A "stretched" version known as theUtility Vehicle, Tracked, Infantry, T56 was also built, and while it held a complete eight-man team, their equipment had to be carried on the outside. Neither was considered very useful.
In 1960 there was a brief study made to replace the Ontos's 106 mm rifles with a new 105 mm design that included arevolver-styleautoloader. This project was not accepted.
Another proposed upgrade was replacing the GMC engine with a newer Chrysler 361 cu in (5.92 L) V8 engine. This upgrade was implemented and the variant was namedRifle, Multiple 106 mm, Self-propelled, M50A1. However, of the 297 vehicles initially accepted by the Marines, only 176 were converted between 1963 and 1965 to this standard.
A mockup was built of an Ontos chassis with a MaxsonM45 quadmount .50 BMG antiaircraft mount.[4]
While the M50 was designed as a tank destroyer, during theVietnam War most M50s did not engage enemy armor as theNorth 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.[2] Its light armor was effective against small arms but vulnerable to mines androcket-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 theBattle of Huế, ColonelStanley 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. InOperation Desoto, the introduction of the largeCH-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.[5]
The Ontos was taken out of service in 1969, and by 1970 were removed entirely from service.[3] 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.[citation needed] 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 theDominican Civil War: on 29 April 1965 an M50 Ontos and anM48 Patton of the 6th MEU engaged and destroyed two rebelL/60L light tanks, each destroying one. In another instance, an Ontos destroyed anAMX-13.[6][unreliable source?]
Of the 297 built, only 14 remain, many of which are the M50A1 model.[3]
There are Ontos on display at the following US locations:
