Ontos, officially the Rifle, Multiple 106 mm, Self-propelled, M50, was a U.S. light armored tracked anti-tank vehicle developed in the 1950s. It mounted six 106 mm manually loaded M40 recoilless rifles as its main armament, which could be fired in rapid succession against single targets to guarantee a kill. Although the actual caliber of the main guns was 105 mm it was designated 106 mm to prevent confusion with the ammunition for the 105 mm M27 recoilless rifle, which the M40 replaced.