Ontos
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Image:Ontos.jpg
Ontos M50A1
The 50-cal spotting rifles can be seen on the upper guns
The Ontos, officially the Rifle, Multiple 106 mm, Self-propelled, M50, was a light anti-tank vehicle developed in the US in the 1950s. It mounted six M40 106 mm recoilless rifles as its main armament, which could be fired in rapid succession against single targets to guarantee a kill. The US Marines were the only force to use the Ontos operationally, and although their crews consistently reported excellent results against infantry during the Vietnam War, the Ontos was always considered an "ugly duckling" and was removed from service in 1969.
The Ontos (Greek for "the thing") project was created to be an air transportable tank-destroyer capable of being lifted by the cargo aircraft of the 1950s. This limited it to a weight between 10 and 20 tonnes, the only other limitation to the design being that it had to use the six-cylinder engine then widely used in the Army's GMC trucks. Allis-Chalmers was awarded the 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 Utility Vehicle, Tracked, Infantry, T55 was a light APC, but only two versions of the prototype were built. This proved utterly impractical due to the limited room inside, carrying only five infantry and forcing the driver to lie prone. A "stretched" version known as the Utility 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. The vehicle which was considered was the Rifle, Multiple 105 mm, Self-propelled, T165. Mounting 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 including new tracks, and a newer turret with about 40 degrees traverse. Only eighteen rounds for the main guns could be carried inside the vehicle due to limited space. Four of the rifles also had 50-caliber spotting rifles attached, firing a round that flew like the 106 mm round and gave off a puff of smoke on impact. A single 30-cal M1919A4 machine gun was also carried for anti-infantry use.
The prototype and testing stage was completed by 1955, at which point the Army cancelled its order. As an anti-tank vehicle the Ontos had several problems, including a lack of ammunition, a very high profile for such a small vehicle, and the need for the crew to exit the vehicle in order to re-load the guns, making them obvious targets for snipers. The Marines Corps, ordered 297. Production ran from 1955 thru 1957. The first vehicle accepted by the Marine Corps was on 31 October 1956.
In 1960 there was a brief study made to replace the Ontos's 106 mm rifles with a new 105 mm design that included a re-loading system similar to that on a revolver. This project was not accepted. However another upgrade was, replacing the GMC engine with a newer Chrysler 361ci, V8 engine. Of the 297 vehicles accepted by the Marines, only 176 were converted between 1963 to 1965. This newest version of the Ontos was named Rifle, Multiple 106 mm, Self-propelled, M50A1.
The Ontos was used widely in Vietnam as a fire support vehicle, and was particularly liked by its crews. They noted that the appearance of an Ontos was usually enough to make the enemy break and run. Nevertheless the Ontos units were deactivated in May 1969, and some the vehicles 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 Viet Nam in 1970, and were cut up for scrap, with some of the chassis being sold off as construction vehicles.