M-50 ONTOS gallery

The original requirement that would lead to the creation of the M-50 Ontos was made by the US Army to obtain an airborne tank destroyer vehicle, weighing no more than 20 tons, armed with recoilless guns that would be effective up to about 3 km distance. It was established that the contract would be for 1,000 units, but when Allis-Chalmers presented the T-165E1 pilot model (on the image), the Army canceled the project and the order. However, the Marine Corps saw the Ontos as a suitable vehicle thanks to its light weight and firepower and decided to order 297 units of the strange vehicle in August 1955.
The M-50 was a small vehicle and had 3 crew members, with the driver housed in the front of the hull and the gunner and loader behind him. The armour protected it from small arms fire and shell splinters, although the Ontos was highly vulnerable to mines. The running gear was made up of four roadwheels, the fourth acting as an idler wheel, with the sprocket in front and without return rollers. The tracks were made of rubber with steel grousers in the center and they were 51cm wide.
The engine installed in the Ontos was the water-cooled 6-cylinder GMC model 302. This engine developed 145 hp, the same as the GMC 6×6 M135 trucks. The transmission was an Allison cross-drive XT-90-2 with the final drives at the front of the vehicle. The maximum speed was about 50 km/h, and with the 178 liters of fuel that it carried it achieved an autonomy of 250 km. It could cross water courses 0.62 meters deep without preparation or 1.50 meters with a special kit and could climb 60% slopes. It could also overcome vertical obstacles of 0.77 meters and cross trenches of up to 1.14 meters wide.
The distinctive feature of the M-50 Ontos was the peculiar arrangement of its armament, which made the vehicle look like a monster with horns. The Ontos pilot model carried six T-170A1 recoilless guns installed in a turret located in the center of the hull. The guns were arranged in two pairs of three guns each, in addition to carrying a 12.7mm T-46E1 machine gun in each trio for directing the fire of the guns. It also carried a 7.62mm M1919A4E1 coaxial machine gun. The turret could elevate to + 20º and depress to -10º and traverse to 15º left or right of center. This first model carried only 18 106mm rounds, 6 loaded plus 12 reloads inside the hull.
The reason for installing so many guns in a single vehicle was to avoid the risk for the gunner as much as possible, since the reloading of the guns had to be done by hand and from outside the vehicle, so the more guns, the less reloads. The production M-50s had some differences with the prototype, for example the 106mm guns were the M-40A1C model and four 12.7mm M8C spotting rifles were installed instead of two, also the internal ammunition stowage was increased to 18 rounds. The guns were mounted on a pivoting fixture on the roof of the hull and now had a traverse increased to 40º to each side of the center.
The six guns moved in unison, but could be fired singly or all at once from inside the vehicle. Usually, a burst of tracer bullets was fired with the M8C spotting rifles to determine the trajectory of the guns, however, the Ontos had a fire control system attached to a T-35E1 periscope. Two of the guns could be easily dismantled and used from the ground if necessary.
In 1963 a variant called the M-50A1 Ontos emerged in which the engine was swapped for a new and more powerful 180 hp Chrysler V8. This modification was carried out on 176 vehicles between 1963 and 1965. In 1969 Detroit Arsenal presented an M-50 chassis with a mock-up of a turret armed with two recoilless guns, designated as “2 man cupola” (on the image). The advantage of this turret was that it allowed both guns to be loaded from inside the vehicle, eliminating the risk of external reloading. The project was not accepted and did not pass the design stage.
The first production vehicle was delivered to the Marines in October 1956, and they were framed in the Anti-tank Companies. The baptism of fire occurred during the 1965 Dominican Civil War, in which Ontos acted as a tank destroyers. In this conflict, the M-50 of the 6th Marines Expeditionary Unit (EMU) destroyed a Swedish Landsverk L-60 light tank and two French AMX-13 light tanks in combat against Dominican rebels. A few years later, the Ontos would suffer its true litmus test in Vietnam.
The US Marines arrived to Vietnam in 1968, and they took their “things” with them. Although the Ontos did not engage in battle tanks, they soon entered combat supporting the infantry or as a static defense, something for which they had not been designed. But thanks to their light weight and excellent mobility, on many occasions they were the only armoured vehicles capable of supporting the “G.Is”, which immediately won them the appreciation of their own, and the fear of the Vietnamese.
In Vietnam, the Vietcong and the VPA’s soldiers quickly learned to flee as soon as an Ontos was in sight. With their six recoilless guns it could tear down a wall with ease, and the effect of the canister ammunition on the massive infantry charges of the Vietnamese People’s Army (VPA) could be absolutely devastating. Many “things” received modifications by the units, such as the installation of powerful lights to carry out night operations. The troops also nicknamed Ontos as “hog” because its interior was filled with dirt and dust when running with the hatches open.
M-50 began to be retired in 1969, though some were transferred to US Army units, which used them until they ran out of spare parts, then using their turrets as fixed defenses. The Ontos always suffered from a shortage of spare parts and having to be reloaded from outside the vehicle always caused serious problems, since many times, the vehicle had to find a covered place, which was not always easy. Its thin armour only protected it against rifle fire, but many were destroyed by mines and by rocket-propelled grenades. The “thing” was only used by the United States which ended up withdrawing them in 1970.

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