Head-on view of one of the most bizarre-looking vehicles ever fielded by the U.S. military: the M50 Ontos.

One of the most bizarre-looking vehicles ever fielded by the U.S. military was the M50 Ontos. Ontos – the Greek word for “thing” — was developed by the U.S. Army as an airmobile antitank vehicle. Panned by the Army, the vehicle was eventually adopted by the Marine Corps.

The M50 Ontos was conceived as a potent, airborne tank destroyer. In November 1950, the farm machinery division of American industrial giant began work designing this beast. 

The requirements laid down by the Ordnance office were basic: The engine would be the inline six-cylinder GMC 302 used in the then-new G-749 family of 2-1/2 ton M135/M211 trucks, it was to be coupled to an Allison cross drive transmission, and its weight and dimension were to permit it to be carried inside the cargo aircraft of the day.

Ontos chassis move along the Allis-Chalmers LaPorte, Indiana assembly line. Early in the program, warping of the armor plates during welding caused alignment problems with the suspension units, which were unique to the Ontos.

Ontos chassis move along the Allis-Chalmers LaPorte, Indiana assembly line. Early in the program, warping of the armor plates during welding caused alignment problems with the suspension units, which were unique to the Ontos.

Within two weeks a design team, at times involving 50 engineers, had completed the design of the M50. Due to the "confidential" classification of this project by the military, a portion of Allis-Chalmers' LaPorte, Indiana, agricultural assembly plant was walled off, and assembly of the prototypes began. The 50-hour test runs required of these vehicles were conducted on the weekends, while the rest of the plant was idle.

An assembly line worker tightens the bolts securing the transmission cover. On the re-powered M50A1 this cover was replaced with a louver.

An assembly line worker tightens the bolts securing the transmission cover. On the re-powered M50A1 this cover was replaced with a louver. 

Of the 1,000 units in the original procurement plan, only 297 were produced.  Beginning in 1955, production ceased in November 1957. The entire series was rejected by the Army. 

Even though the Ontos carried only a three-man crew, space was at a premium, and oftentimes the vehicles were operated with the rear door open. Because so little space was available for stowage only a minimal amount of ammunition was carried. The Ontos was to enter combat with a round in each of its six rifles, eight more in a storage rack beneath the floor, accessible through a door beneath the vehicles rear hatches, and four more rounds stowed in a rack inside the vehicle.

Even though the Ontos carried only a three-man crew, space was at a premium, and oftentimes the vehicles were operated with the rear door open. Because so little space was available for stowage only a minimal amount of ammunition was carried. The Ontos was to enter combat with a round in each of its six rifles, eight more in a storage rack beneath the floor, accessible through a door beneath the vehicles rear hatches, and four more rounds stowed in a rack inside the vehicle.

While this vehicle looks like a M50 Ontos, this vehicle is actually a T165, a development model. The suspension and rear doors were different, but the general layout remained the same in the production model.

While this vehicle looks like a M50 Ontos, this vehicle is actually a T165, a development model. The suspension and rear doors were different, but the general layout remained the same in the production model.

An array of On Vehicle Material, including two large tripods for dismounted use of two of the recoilless rifles. Between the tripods in this display is the M191A4 Browning .30 caliber machine gun. Though normally mounted on the turret at the commander’s hatch, a tripod was also provided for its dismounted use as seen here.

Despite its small size, the Ontos carried an array of On Vehicle Material, including two large tripods for dismounted use of two of the recoilless rifles. Between the tripods in this display is the M191A4 Browning .30 caliber machine gun. Though normally mounted on the turret at the commander’s hatch, a tripod was also provided for its dismounted use as seen here. Between the Browning and the tripod to the left of this photo is another of the crew’s weapons, the M3A1 .45 caliber submachine gun.

The Marine Corps was interested, however, and took delivery of the vehicles. One hundred seventy-six of the vehicles were re-powered with a Chrysler 361 cubic-inch V-8 (some sources say 294) beginning in 1963. This required redesigning armored engine covers. The new cover extended forward of the rifle’s travel lock, and engine access door gained louvers. With the new powerplant the vehicle was re-designated M50A1.

Probably the biggest drawback to the Ontos was the requirement that a crewman exit the vehicle to reload the main guns. The 38-lb. 106mm round had a maximum effective range of 3,000 yards.

Probably the biggest drawback to the Ontos was the requirement that a crewman exit the vehicle to reload the main guns. The 38-lb. 106mm round had a maximum effective range of 3,000 yards. With few Vietnamese armored vehicles to engage, in Southeast Asia the Ontos saw extensive use as an antipersonnel weapon. With Beehive rounds in each of the six tubes, the Ontos could release a hail of flechettes that would penetrate even the densest jungles up to a quarter mile, obliterating both foliage and man. 

As designed, the Ontos was to roll into combat with a round in each of its six rifles, eight more in a storage rack beneath the floor, accessible through a door beneath the vehicles rear hatches, and four more rounds stowed in a rack inside the vehicle. While the six M40A1C 106mm recoilless rifles gave the Ontos tremendous firepower, its shortcoming was the requirement that the vehicle be opened up and a crewman expose himself in order to reload.

Period color image of a Marine Ontos in the field

A USMC Ontos in the field. 

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