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M50
M50A1

Multiple 106mm Self-propelled Rifle M50^1-8

The M50, known as the Ontos, mounted six recoilless rifles, 3 per side, on a small turret atop its pyramid-like hull. The rifles were actually 105mm in diameter, but were dubbed 106mm rifles to prevent confusion with earlier 105mm rifles and ammunition. The .50cal spotting rifles were mounted on top of the upper 106mm weapons, and the .30cal MG mount was in the center on the turret roof. The rifles were numbered 1 through 6 clockwise starting with the bottom left rifle when looking at them from behind the vehicle; although any rifle could be quickly dismounted for ground use, rifles 2 and 5 were specifically designated for this and consequently their spotting rifles were not used when mounted on the vehicle. The spotting rifles were ballistically matched to 1100 yards (1000m) and could be used to 1500 yards (1400m), beyond which burst on target was the preferred spotting method. The rifles could be fired singly or in combination up to all six at once. The suggested single firing order was rifle 1, 6, 2, 5, 3, 4 in order to maintain the maximum two-rifle salvos at all times, and the recommended two-rifle firing order was rifles 1 and 6, 2 and 5, and 3 and 4 in order to maintain turret balance. Crew doors included a driver's hatch in the front of the vehicle, a hatch in the turret, and double doors in the rear. Besides the six 106mm rounds stored in the loaded rifles, there was an eight-round ammunition compartment in the vehicle's bottom rear, and four more rounds were stowed in the right rear of the gunner's compartment. The 106mm rifles could only be loaded from outside the vehicle. The M40A1C rifle differed from the M40A1 by having a projectile indicator on the tube, and the bottom of the breechblock operating lever was arranged so that it could be engaged by the hydraulic actuator that allowed the breech to be opened or closed from the gunner's position.

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Multiple 106mm Self-propelled Rifle M50A1^1-2,9-11

The M50A1 got a new engine and transmission, and can be differentiated from M50 by the additional cooling louvres on the engine and transmission access doors as well as above the engine compartment to the right of the driver.

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References

1. Hunnicutt, R.P. Sheridan: A History of the American Light Tank, volume 2. Navato, CA: Presidio Press, 1995. Reprinted with permission from Sheridan, R.P. Hunnicutt ©1995, available from Presidio Press, 505B San Martin Drive, Suite 160, Navato, CA 94945.
2. Estes, Kenneth W. M50 Ontos and M56 Scorpion 1956-1970: US Tank Destroyers of the Vietnam War. Oxford: Osprey Publishing Ltd., 2016.
3. TM 9-2350-212-12 Operator's and Organizational Maintenance Rifle, Self-propelled, Full-tracked: Multiple, 106-mm, M50. Washington, DC: Headquarters, Department of the Army, 11 December 1959.
4. MICO P1550.228 The Ontos. Washington, DC: Marine Corps Institute, 12 March 1962.
5. FMFM 9-3 Antimechanized Operations. Washington, DC: Department of the Navy, Headquarters US Marine Corps, 5 July 1967.
6. Crismon, Fred W. U.S. Military Tracked Vehicles. Osceola, WI: Motorbooks International, 1992.
7. LFB-23 Employment of the Antitank Battalion. Washington, DC: Headquarters, United States Marine Corps, 23 December 1959.
8. Olcer, Dr. Nuri Y., et al. Engineering Design Handbook: Recoilless Rifle Weapon Systems. Alexandria, VA: Headquarters, US Army Materiel Command, 15 January 1976.
9. TM-00545B-10 Rifle, Self-propelled, Full-tracked, Multiple 106mm, M50A1 Operation and First-echelon Maintenance. Washington, DC: Headquarters, United States Marine Corps, 30 December 1963.
10. TM-00545B-35/1 Rifle, Self-propelled, Full-tracked, Multiple 106mm, M50A1 Field and Depot Maintenance. Washington, DC: Headquarters, United States Marine Corps, 15 January 1964.
11. Estes, Kenneth W. Marines Under Armor. Annapolis, MD: Naval Institute Press, 2000.

*The dimensional table for the M50 was compiled from information reprinted with permission from Hunnicutt's Sheridan. That for the M50A1 was compiled from TM-00545B-10. Any inconsistencies should presumably simply be chalked up to differences in source data and not to actual differences in production.

Last updated 6 Jan 2024.
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