When the United States needed an air-transportable tank destroyer in the early 1950s, something that they had been searching for during World War II, a joint effort of the US Army and US Marines brought them to what was called the M50 Ontos. The small, compact, yet powerful enough vehicle was light enough to be airdropped, just as the Marines needed, but why was it still removed from service in 1969?

The Thing

During World War II, when the first attempts to create such a vehicle were made, the limitations in cargo aircraft carrying capacity limited the vehicles’ armor and firepower capabilities, making them no match against the enemy tanks. Come the early 1950s, the US Army and Marines came up with the project known to be the M50 Ontos. In the end, only the Marines would continue using the compact vehicle.

M50’s name “Ontos,” was a Greek word that translates to “thing,” which was the perfect word to describe such a strange vehicle.

105mm Self-propelled Rifle M50A1 Ontos. (US. Army, Public Domain, via Wikimedia Commons)

Producing a vehicle that was compact enough to be airlifted to the battlefield yet powerful enough to match the enemy tanks was indeed a challenge. According to the calculations made by the engineers, the tank destroyer had to be around 10 to 20 tons for it to be air-transportable but still capable enough to fight and survive on a battlefield.

Perfect Match

The M50 was the perfect match with its small, low-profile fully-tracked hull and an enclosed compartment for the crew. To achieve its air-droppability, the engineers had to adjust the armor protection by putting a 13 mm on the hull and just 6.5 mm on the underside to make it light enough.  This would be enough to stop small arms and splinter protection from artillery but not much else.

If this was a bit of a let-down, then you have to check the M50’s main armament: six 105 mm recoilless rifles. To avoid confusion with the M27 recoilless rifle, the M50’s rifles were named 106 mm. A recoilless rifle was installed instead of the conventional anti-tank cannon because the vehicle was so small that recoil from a heavy gun would tear it apart. The Recoilless rifles, on the other hand, balanced out most of the recoil forces by venting propellant gasses out of the weapon’s rear when firing. This clever technique is effective in counteracting the recoil and allows the rifle to fire a larger caliber round compared to conventional weapons of the same size and weight. The barrel can also be thinner to save additional weight.

A marine Ontos crew member relaxes during a break in the fighting at Hue. (National Archives at College Park, Public domain, via Wikimedia Commons)

The rifles could be fired individually or all at the same time. When the six rifles were fired all at once, the back blast of the M50 could blow bricks out of a nearby building and shatter the glass on nearby cars.

The semi-traversable turret where the guns were mounted could rotate up to 40 degrees per side. The guns could be elevated up to 20 degrees and depressed 10 degrees. Ontos used .50 caliber ranging guns on the rifles, with performance similar to the main armament. The ranging round would glow brightly as it approached the target and then emit a white smoke once it hit it. This would be the aiming reference of the gunner.