M50 Ontos

The Rifle, Multiple 106 mm, Self-propelled, M50 Ontos was developed as an air-transportable tank destroyer for the United States military. Designed by Allis-Chalmers starting in 1952, the vehicle was intended for transport by cargo aircraft, which necessitated a restricted weight profile and the use of a standard six-cylinder gasoline engine. Allis-Chalmers produced pilot vehicles based on the running gear of the M56 Scorpion. Although the United States Army canceled its order in 1955 following testing at Aberdeen Proving Ground, the United States Marine Corps adopted the vehicle, with production occurring between 1955 and 1957.

The M50 features a cast steel turret with two external arms each holding three M40A1C recoilless rifles. These six main guns are manually loaded and can be fired in rapid succession. Targeting is facilitated by four .50 caliber spotting rifles mounted to the main guns, which fire tracer rounds that follow the same trajectory as the 106 mm ammunition. The vehicle is operated by a crew of three: a driver, gunner, and loader. Internal space limits the ammunition load, and the loader must exit the vehicle to reload the external rifles. Secondary armament consists of a single .30 caliber M1919A4 machine gun. The armor provides protection against small arms fire but is vulnerable to mines and rocket-propelled grenades.

The United States Marine Corps operated the M50 from 1956 until 1969. It saw combat during the 1958 Lebanon Crisis, the Dominican Civil War, and the Vietnam War. In the Dominican conflict, M50 units engaged and destroyed L/60L light tanks and an AMX-13. During the Vietnam War, the vehicle was primarily employed in a direct fire support role against infantry and fortified positions. It was utilized in the Battle of Huế to breach walls and was frequently deployed in static defense positions. The vehicle's weight permitted movement across pontoon bridges and transport via heavy-lift helicopter slings. Following its withdrawal from frontline service in 1969, some units were transferred to a United States Army light infantry brigade for use until spare parts were exhausted. The remaining vehicles were removed from service in 1970.