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 metric tons, 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. /wiki/Allis-Chalmers" rel="nofollow - - M56 Scorpion light anti-tank vehicle. The vehicle mounted 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 with the target. This meant that the 106 mm recoilless rifles were lined up with the target, and then they would be fired. A single .30 caliber /wiki/M1919" rel="nofollow - - 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.

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 /wiki/Revolver" rel="nofollow -