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Although the Army had abolished the tank destroyer as a concept and equipment after

WWII, and the Marine Corps mimicking with the M3 GMC had ended in 1944, the

Marine Corps development of the M50 Ontos (Thing) must be considered as areversion to that doctrine.

The installation of a Chrysler 361B engine developing 180 hp and new track during1963-64 produced the M50A1, which had sufficient automotive improvements to enable

it to reach designed speeds.

The criticism of the M50 Ontos increased with an unusually poor provisioning of spares

upon introduction and the quartermasters admitted a total lack of parts in the FMF.

Moreover, the effectiveness of the 106mm recoilless rifle as a tank killer looked inferior

to the new generation of antitank guided missiles now entering service. Even the MarineCorps Reserve saw inadequacies, as only two Ontos per company were provided as

training vehicles.

During the dry weather period in Vietnam (March-September) officers like LtCol. WalterMoore, a tanker since 1944 now commanding the 1st Antitank Battalion, urged the

infantry regiment and division commanders to make greater use of the vehicles and theirfirepower to provide direct fire support to the infantry and to conduct motorized

reconnaissance. Moore chafed at the use of Ontos for protecting command posts, artillery

positions and bridges (the saying went, two on the ridge, three on the bridge for suchtank and Ontos platoon missions),

The Battle for Hue began on 30 January, when eight battalions of NVA infantry

infiltrated the city and the NVA 2d Division threatened to reinforce. The respondingMarine Corps forces included tank platoons from both 1st and 3d Tank Battalions, and

Ontos of A Company, 1st Antitank Battalion. Here, with the enemy in known andobservable positions, the armored vehicles gave key support to the embattled infantry andundoubtedly provided the measure of superiority. The key Marine Corps infantry

battalion commanders fighting there differed in their opinions but valued the support

equally. LtCol. Ernest Cheatham, commanding 2/5, liked the Ontos for its speed andagility and thought that the tanks drew too much fire. LtCol. Robert Thompson of 1/5

preferred the tanks for their armament and staying power. Both tanks and Ontos received

frequent hits by RPG and recoilless rifle rounds. Several tanks went through up to five

crews and remained in action. Three of the Ontos stayed knocked out of action when hit.Most commanders rated the 90mm fire best, provided that the tankers had and used

concrete piercing fuzes on their HE rounds. Otherwise, the 106mm projectiles of the

Ontos worked better in knocking down buildings and walls to facilitate the infantryadvance. Both Thompson and Cheatham had to hold up their advance at times for lack of

90mm and 106mm ammunition, illustrating the essential role of their armored fighting

vehicles.

Ironically, the Army made some use of excess Ontos acquired from the Marine Corps in

Vietnam. Formed in Company D, 16th Armor, for use with the 173d Airborne Brigade,

the former Marine Corps vehicles gave good support to the troops when flown into action

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by the flying crane heavy lift helicopters supporting the Brigade.

The last operational Ontos stationed with the Guantanemo Bay garrison continued tooperate until April, 1980, by then with only one vehicle still operational and two used for

parts.