M50 Ontos: The Forgotten Tank-killer
It is the tradition in the U.S. Army to name its tanks after great generals. Over the years there has been the Stuart, the Grant and Lee, the Sherman, the Patton, the Pershing, the Abrams, the Sheridan, the Chaffee, and the Bradley. But there was one armored vehicle that was so singularly odd and strange looking, it didn’t get named after anyone, lest perhaps, some insult might be taken. Instead, the name it got handed was Ontos, the Greek word for “thing.” It was an apt name. With its tiny chassis, tinier turret and six, massive, externally mounted recoilless rifles, the M50 Ontos had to have been the strangest armored vehicle ever to make it into the American military inventory.
Except for some Marine Vietnam veterans, the Ontos is, today, almost wholly unremembered. The reason has less to do with the Ontos’ battlefield performance, which at times was stellar, than it did with the fact that only about 300 were ever built, a little more than half of which survived up to the time of the Vietnam War. It meant there weren’t enough Ontos to engage the tactician’s imagination and so it never featured in tactics problems in the basic schools. There was never a military occupational specialty for Ontos crews. Officers might serve in an Ontos unit for a tour, but then they’d move on to something else and whatever they’d learned from it never really entered into the institutional memory. Another reason was that Ontos was designed as a tank killer, but since the North Vietnamese Army (NVA) only rarely used tanks, Ontos was used mainly as an ad hoc weapon.
But fight it did, distinguishing itself at Hue, Khe Sanh, and countless other battles. For all its out-and-out eccentricity, Marines found it handy to have around because it was nimble and fast. Thanks to its relatively light weight, Ontos fairly glided through swamps and rice paddies, where heavier vehicles wisely feared to tread. And Ontos packed a punch that was way beyond its weight class. For this reason, the NVA feared it and avoided the Ontos wherever possible.
If there was a general after whom the Ontos should have been named, it probably would have been Lt. Gen. James Gavin, wartime commander of the 82nd Airborne Division. After the war he wrote a book called Airborne Warfare, outlining his vision for using airborne forces in future wars. Part of it involved using air-transportable mechanized forces as a kind of light cavalry, capable of doing reconnaissance, and when necessary, laying extremely deadly ambushes against enemy armor. In the spirit of cavalry, such vehicles would have to sacrifice protection in favor of speed, agility, and ability to deliver serious firepower.
The Ontos program began in November 1950 as a joint Army-Marine Corps program. The development contract went to Allis Chalmers’ Farm Machinery Division, with the work being carried out at the company’s Agricultural Assembly Plant in LaPort, Ind. According to legend, the spec sheet they developed it from was only one-page long. Among the few things that it specified was that its running gear would be based on the M56 Light Anti-Tank Vehicle and that it would utilize the same six-cylinder, inline gas engine common to all the military’s 2½-ton GMC trucks.
In 1953, the prototype was presented to the U.S. Army, and they immediately hated what they saw. They hated that it was so small and too tall and that there was not enough room inside it, either for the three-man crew or for ammunition for the recoilless rifles, of which only 18 rounds could be carried. They didn’t like that the turret was so shallow, really little more than a cast steel turntable and hatch in the middle. They hated that the six recoilless rifles that made up its armament were externally mounted and had to be reloaded from the outside. They didn’t like that the half-inch armor plating on the sides wouldn’t protect the crew members from anything larger than .50 caliber machine gun rounds, and that the underside’s armor plate was not even half that thick, making it totally vulnerable to mines or anything that might explode underneath it. The Army backed out of the project, canceling their share of the 1,000 vehicle order.
The Marines, on the other hand, were not nearly so fussy. They liked that Ontos was so fast and agile and seemed capable of going anywhere they went, which was more than could be said about most tanks. They accepted that instead of being able to fight it out with enemy tanks, the Ontos would have to “shoot-and-scoot” to a place where it could safely reload. As for its pronounced lack of protection, they shrugged. For Marines, being shot at was nothing new. They placed an order for 297 Ontos. The production contract went to Allis Chalmers, which started building them in 1955 and finished in 1957, with the first vehicle accepted by the Marine Corps on Oct. 31, 1956.
The Ontos’ official name was: “Rifle, Multiple 106 mm self-propelled M50.” At its heart was the M40 106 mm recoilless rifle, a weapon which had been developed after World War II as a tank killer, based on the earlier M27, 105 mm recoilless rifle, which turned out to have a number of key deficiencies. The rounds the M40 fired were not, in fact, 106 mm, but 105 mm, but were designated as 106 mm to keep from being confused with the M27’s round, which was not compatible with the M40. The M40 had the accuracy, the range, a serious punch forward and a serious kick aft. During the Ontos’ testing at the Army’s Aberdeen Proving Ground in Maryland, all six guns were fired at once and the backblast was so great that it knocked bricks out of nearby buildings and shattered numerous car windows.
The powerful recoilless rifles’ accuracy was greatly aided by attaching .50 caliber spotting rifles to four of the Ontos’ six M40s. The rifle fired a tracer round whose trajectory, at least for the first 1,100 yards, was nearly identical to the M40s, and it marked the spot it hit with a visible puff of smoke. The spotting rifle’s own range was only 1,500 yards, and hitting targets beyond that required burst-on target and bracketing techniques of fire adjustment.
The first time Ontos was deployed was during the Lebanon Crisis of 1958. Since it was a peaceful intervention, it saw no action. Six years later it did go into combat during the American intervention in the Dominican Republic of 1964. There it encountered and promptly destroyed several enemy tanks, including a French-built AMX-13 and an old Swedish L-60. It was the only time the Ontos ever performed the mission it was built for.
Then came Vietnam. In 1965, during the initial American buildup, the Marines sent over two anti-tank battalions equipped with Ontos. With no enemy tanks to fight, the Ontos companies were quickly spread out and attached to other units. The problem was, with no doctrine in place for them other than for fighting tanks, the Ontos were used or not used largely according to the whim of the commander of whatever units they were attached to.
Though they quickly proved themselves as highly capable infantry support weapons, providing excellent frontal fire and flank protection, the Ontos had some serious shortcomings. After one or two would get destroyed by mines or rocket-propelled grenades, their unit commander often found his enthusiasm for them considerably dampened and relegated them to static defense duties. Another problem that plagued the Ontos was repeated accidental firings of its recoilless rifles because of too-tightly adjusted firing cables.
Even so, the Ontos continued to be deployed supporting infantry. Using HEAT rounds, the Ontos was an excellent bunker-buster. But where it truly excelled was as an anti-personnel weapon. A “beehive” round was developed for the M40 that, upon exploding, unleashed a massive whirlwind cloud of nearly 10,000 steel flechettes. As a result, the VC and NVA were terrified of the Ontos and avoided it wherever possible.
In December 1967, the Marines reorganized their anti-tank battalions and as a result, the Ontos units were all attached to tank battalions. By this point, the Ontos was becoming worn out. Treads and other replacement parts were becoming difficult to obtain. Increasingly, Ontos were being cannibalized to keep others operating. It was already obvious its days were numbered. Then, on Jan. 30, 1968, the NVA launched the Tet Offensive. It was one of the longest and bloodiest battles of the entire Vietnam War, nowhere as hard fought as in Hue City.
For the Ontos, the battle was its shining moment of glory. After the American and South Vietnamese forces cleared the south bank of the Perfume river, the 1st Battalion of the 6th Marine Regiment reached the Citadel. A number of Ontos were brought up and one by one, began taking out the buildings where the enemy were holed up. One of the Marine officers leading the siege of the Citadel later identified the Ontos as “the most effective of all Marine supporting arms,” in the Battle of Hue. At the same time, the NVA siege of Khe Sahn was also under way. With the threat of NVA armor anticipated, 10 Ontos were airlifted into Khe Sanh by MH-53 helicopter, and incorporated into its defense. There, the Ontos also performed with distinction.
A year later, the Marines deactivated their Ontos units and the vehicles were handed over to the Army’s light infantry brigade. The Army used them until their parts ran out and then employed them as bunkers. What happened to them after that is largely unknown.
After Vietnam, some were handed over to civilian agencies and used as forestry vehicles. A tiny number made it into collectors’ hands. Some are in museums. According to Mike Scudder, a former Marine who owns several, there are more World War I tanks in circulation than there are Ontos. This may not actually be true, since there are believed to be more than 60 Ontos sitting discarded in the desert on a Marine Corps reservation near China Lake, Calif. If they are still there, no one is saying.