"the thing" in Greek. As applied to the Marine's armoured
vehicle, it could mean "the rare thing". This armoured vehicle
made significant contributions to the success of Marine and Army
infantry operations in Vietnam, but less is known about the vehicle than
any other armoured vehicle produced by the US military. Even
among military vehicle collectors, the name Ontos often draws blank
The reasons may stem from the fact that the
Ontos was produced in small numbers. Only 176 vehicles are known
to have been in the Marine Corps at the start of the Vietnam War.
Another factor is the Marine Corps quickly disposed of the surplus
vehicles; removing much of the hulls and gun mounts. With so few
examples of surviving Ontos making it into the hands of museums and
collectors, its story didn't get told. There are more surviving
WWI tanks today than Ontos.
The Ontos was a
relatively light weight tracked armoured fighting vehicle that was
designed in the early 1950's to destroy the main battle tanks of this
era using the firepower from its six 106mm recoilless rifles. Its
diminutive size, 12 ½' long, 8 ½ ' wide, crammed three crewmembers
into a compartment slightly higher than 4'. It served the US
Marines from 1956 until the bulk of them were dismembered in 1970.
Its service to the Marine coincided with the Corps's use of the 106mm
The Ontos would be
more than 10 years into its life cycle before it would be tested under
fire. The first test would be against the Dominican rebels
in April of 1965. The
second test was in the environment of Vietnam;
and its role would have no relationship to what was originally intended
for this fast little tank killer.
If it is true that
an army fights its present war with tactics and equipment from its last
war; then it is the mark of a successful army to be able to adapt in
order to accomplish the new mission. The Ontos and its crews
had to convince the Marine Corps leadership that this fighting vehicle
had a role in Vietnam. The success, at convincing its leaders of
the Ontos's potential, is mixed. The men that made up the Ontos
crews attest that it was only at the company level that they convinced
leadership of the enormous firepower that could be available to the
grunts; firepower that could change the outcome of a fire fight.
I am struck at the
similarities of the Ontos's role within the Infantry Company and the
role of the little Stuart tank used by the Marines in the pacific
battles of WWII. Both were lightly armoured and vulnerable to the
destruction by weapons above 50-caliber. Both of these vehicles
were effective because they were small yet could carry relatively high
firepower into an infantry fire fight. Their size allowed them to
go into areas the larger tanks could not.
The 20" wide tracks
of the 9-ton Ontos would allow it to go on the soft soils surrounding
the rice paddies of Vietnam. They both served as bunker busters.
Both vehicles lessened the infantry's causalities by being close to the
fight; and could be quickly deployed to overcome an enemy's fixed
The Ontos carried
the beehive round that sent out a hundred darts per firing to clean out
a jungle of its enemy. There
was no other weapon that could clear a jungle for a depth of a ¼ mile
like the 106mm recoilless rifle using the beehive round.
Artillery shells and bombs effectiveness was cut to the area of a direct
The jungle vegetation absorbed both concussion and
fragmentation. The other vehicles that mounted the 106mm
recoilless rifle were open to enemy small arms fire. The Ontos
could expose itself to enemy small arms for the short time it took to
empty its 6 guns and depart to a more secure position to reload.
It was an armoured
the North Vietnamese Army feared it.
It is no surprise to
the veteran of any country's army that weapon systems get misused,
unsupplied and/or forgotten by the generals that demanded their
development. The Ontos fell into this grouping.
Deployment of the Ontos seemed like an after thought to many commanders
and the Ontos's parts replacement was a serious concern. It is a
testament to the men that manned this small armoured fighting vehicle
that some important history was written by its participation in Vietnam.
The Ontos was
designed in another era for another purpose. Developed to kill
tanks; the Ontos found itself outmoded before it was in the hands of its
first crewmen. It was left to the men who manned the Ontos to
reinvent it; and they reinvented it into a weapon that served the Marine
The Ontos crews were
pulled from the Marine Infantry Battalions to learn the trades of
gunners, radiomen, mechanics and tacticians. The Marine
designations for jobs within the infantry battalion were in the series
0300. The Ontos's crews carried variations on these job numbers.
Some crewmen were motor transport or track maintenance trained, but most
were more likely to be former
After their tours with the anti-tank units, they were just as likely to
return into the battalions from which they came as to be reassigned
another anti-tank unit.
The Marine high
command was single minded in pitting the Marine Infantryman against the
North Vietnamese Army and Viet Cong veterans. They felt,
with good assurance, that the individual Marine, coupled with
traditional artillery and air cover, could defeat this enemy without any
distractions from those weapons not carried to the field by their enemy.
that Vietnam was not conducive for tank operations. If it were,
the NVA would have fielded armour. Since tanks were not fielded by
the NVA, then there was little use for the small anti-tank known as the
Ontos also known as a "pig".
The Marines carried
its' M48A2 tanks and Ontos into the fields of battle, but they didn't
command the focus of the Regimental and Battalion Commanders as did the
traditional attachments such as the 81 and 4.2 mortars, 105mm artillery
and close air support. The Ontos's deployment was often a knee jerk
decision by Battalion Commanders. They were used mostly as
perimeter defence with some convoy duty.
Vietnam was run by
our politicians; with rules of engagement that totally distracted the
military commander. Our air power was forbidden to knock out the
surface to air missile sites that depleted their ranks. In early
Vietnam, the enemy could retreat to areas forbidden to US forces.
These rules as applied to the Ontos crews decreed that all major calibre
weapons had to secure Battalion authority before being loaded or
early Ontos crews were expected to go into combat areas unloaded.
Later, they could have 106 rounds in the guns, but had to secure
authority to fire.
These rules would
have given nightmares to WWII or Korean War veterans. If the Marine
Commanders ignored the attributes of the Ontos, the NVA didn't. In
almost all my interviews with Ontos Crewmen, one point was brought
up. The NVA was frightened of the Ontos and would avoid
contact if possible. Most contact between NVA and the Ontos was
inadvertent on the part of the enemy.
The Ontos project
was awarded to the Allis-Chalmers' farm machinery Division of Wisconsin
around the early part of November 1950. The Allis-Chalmers
engineering section was comprised of about 50 to 60 engineers; 90% of
which would eventually work on the development of the first prototypes.
All the prototypes were constructed in the Agricultural Assembly Plant
in LaPort, Indiana.
The project was
first envisioned by the government to be an air transportable tank
destroyer capable of being lifted by the cargo aircraft of the 1950's.
The contract was to be for 1000 vehicles to be delivered to the
Army. In 1953, the army would refuse to accept
delivery of the Ontos. At this point the Marines accepted delivery
of about 300 vehicles.
Ordinance Command, represented by Chief Engineer Carl Holmyard,
delivered only one page of specifications. The specifications
demanded that the vehicle would be powered by the same GMC six cylinder
gas engine that was standard for the 2 ½ ton military trucks of the day
and a front mounted Allison cross drive transmission that would carry
power to the tracks. The remainder of the specifications
restricted the outside dimensions and weight so as to be air
The project was
This is the lowest security
classification for government work, but it still required that the
prototypes be built in a walled off section of the Agricultural Division
Assembly Area. The government would accept the prototypes for
testing only after the machines had 50 hours of running time. This
required the engineering section to come to the plant on weekends and
drive the prototypes around the grounds of Allis-Chalmers.
The Ontos had two
large arms that held the six recoilless rifles. These arms were
joined to a shallow turret. This entire assembly was cast in armoured
steel. The early prototypes could swing the guns less than
15 degrees left and right. The production Ontos was modified to
turn the guns 40 degrees left and right. The welding of the Armoured
hull was a problem for Allis-Chalmers. It took the failures of
several prototypes to develop the proper welding techniques.
The first prototype
Ontos had a track system similar to that used on the self propelled
artillery vehicle called the Scorpion. This track system was later
changed. This first Ontos prototype is still in existence and in
the hands of Mr. Fred Ropkey. The later and final track system and
suspension was of a new design. Each track consisted of two
sections of rubber; 48" long with steel drive teeth in the centre.
Twenty-inch wide steel grousers held the rubber and the drive teeth
together. It took 5 sections of track to make up a complete track.
A well-motivated crew could accomplish a track section replacement in
about 1½ hours. One crewman told me that a crew made a track
repair in 42 minuets.
system was designed so that no mechanisms intruded into the already
small interior of the fighting compartment. The road wheels hung
on torsion bushings that were attached to the sides of the hull.
There was much development in the special rubber compounds for the
The rubber bladder
gas tank was mounted in the front of the vehicle directly behind the
glacis plate. It was cast of rubber and contained a tube-shaped
void through its centre to allow the left drive shaft to pass through
the fuel tank on its way to the left drive sprocket.
developed a deep water fording provision for the Ontos that was not
accepted by the Marines. It consisted of a waterproof covering for
the engine. The motor would stay dry while fording.
The fording gear had to be carried and installed on the Ontos prior to
One of the problems
that had to be overcome by Allis-Chalmers involved the track alignment.
The lower chassis was constructed as a weldment. The distortion
involved in the welding process caused the suspension to become
out-of-line; and so the track would be thrown. Machining the lower
hull, where the track suspension parts bolted to the hull, finally
solved the problem.
developed a personnel carrier based on the Ontos track design. The
personnel carrier had one additional 48" track section. No
photos are known to exist of the personnel carrier prototype.
Much of the
engineering work was completed in 1950 during a two-week design
marathon. The Marine Corps continued to test the vehicles for the
next six years until the vehicle was accepted in late 1956. A
review of the chief engineer's notes for 1957 through 1959 showed a
continuing series of revisions.
These notes, of Chief Engineer
Craig Cannon, referred to a major revision of the Ontos called the
"1960 project". Some of the proposed revisions
called for an aluminium amphibious hull and two 105mm recoilless rifles
(designated as T237 guns) fitted with a cylinder similar to a revolver
pistol. This change would have allowed multiple firings of the two
guns without the need for a crew member to reload the guns from outside
the vehicle. Another major revision would involve the replacement of the
engine with a turbine engine.
Project" was never accepted. One of the early tests involved the
acceptance of the aiming system of the six gun turret. Part of the
test included the firing
of all six guns at once.
The test vehicle was taken to the Aberdeen testing facility that had
been built for the testing of the 106 recoilless rifle. No one
envisioned the effect of six of these weapons going off at once, least
of all the people who designed the testing facility. The back blast
from the firing knocked bricks out of a nearby building and knocked the
rear windows out of several cars.
to later refurbish the Ontos: removing the 6 cylinder engines and
replacing them with the 361 cubic inch Chrysler V8. The change
over involved redesigning the armoured engine covers with additional
venting. It is believed that, of the 300 delivered units, only 176
Ontos were refitted.
THE ONTOS ARMOURED
glacis plate of the Ontos is 1" thick. The glacis plate forms
the front of the hull and would protect the driver and transmission from
ground level to 27"in height. The side plates that hold the
track suspension parts and form the sides of the crew compartment are
slightly heavier than 1/2" thick. The floor of the fighting
compartment is ¼" thick of non armoured steel. The majority
of the remainder of the hull is formed from ½ thick armour. The
front engine covers are cast of armoured steel and its louvers have a
3/8' bead formed on the inside lip of each louver to defeat the entry of
small arms fire from entering the engine compartment.
It has been
speculated that the Ontos was top heavy and tended to overturn easily.
I found that with the top hull, gun mount and guns removed, the vehicle
still weighed in at more than 11,000 pounds. This 11,000 pounds would be
contained within the height of the tracks (34"). I therefore
doubt that the Ontos was seriously top heavy. Crewmembers have
told me that the vehicle would slip sideways if traversing a steep hill
before it would roll over.
Recoilless Rifle Firing System
The Ontos had the
ability to fire its 106 recoilless rifles one at a time or as many as
all six guns at once. Four of the six guns had 50 calibre
spotting rifles attached. The flight of the 50 calibre spotting
round approximated the flight of the 106 round. This round was
constructed as a tracer with a smoke puff that appeared on impact.
The firing of the weapons was directed by the gunner; who had a seat to
the rear of the driver and engine.
The gunner would often first
fire the spotting round at the desired target and watch its flight.
Often, even prior to the spotting round hitting the target, the 106
round would be sent on its way. The maximum effective range for
the 106 round was 3,000 yards. The 106-MM rifle was generally
considered a direct fire weapon, but the crews were taught, and used,
indirect fire at targets not within sight of the gunner.
recoilless rife is more than 11' long and weighs about 288 pounds each.
The turret of the Ontos had to carry this 1,700 plus pounds over uneven
ground. The strain on the gun mount required the crews to realign
the guns from time to time.
Two of the six
rifles were designed to be easily removed from the vehicle and used with
a ground mount should it be required.
There were three men
to an Ontos: driver, commander/gunner and loader. If the Ontos was
carrying a lot of ammunition and/or other gear, or if the weather was
extremely hot, you could find the loader sitting on the driver's hatch,
riding on the machine gun crossbar or riding in the platoon's ¾ ton
Dodge truck that often escorted a platoon movement.
could and did drive with the rear doors open on occasions. This
mode of travel would roll road dust into the interior making the crew
look like pigs. For this reason the crews usually referred to the
Ontos as a "pig".
The training of the
crew varied as the demands of the war changed. The early crews,
prior to March 1965, were trained at Camp Horno in the home of the 1st
Marine Division, Camp Pendelton on the coast of California near Los
Angeles. The training of later crews were assigned to units
that trained them in the field. They had to learn: vehicle
maintenance, small arms, tactics and direct and indirect fire.
All Marines were trained in small arms, but the Ontos crews also carried
a sub-machine gun that was not used by most Marine units. They
also had to know how to operate the three main radios and intercom.
Some of the Vietnam assigned crews went to the firing ranges on Okinawa
for extensive day and night-time firing of the 106MM rifles.
The Ontos crews were
required to replace the 48" long sections that made up the track.
They also tightened the track adjustment when a track was repaired or
when a series of hard turns stretched it. An Ontos mechanic was
assigned to each platoon, but the crewmen had to assist to keep the
machines running. The platoons were often separated when assigned
to infantry units.
The platoon mechanic was often
unavailable to make a repair when needed. Replacement parts were
often rare or non-existent. Many Ontos were turned into parts
vehicles due to poor parts supply.
The Ontos platoons
were organized into heavy and light sections. There were three
Ontos in a heavy section and two Ontos in a light section. There
were three platoons to a company; and three Companies to an Ontos
Battalion. The 1st and 3rd Ontos Battalions saw action in Vietnam.
The machines were in Vietnam from early 1965 to mid 1969.
There is some evidence that at the end of 1965 there were 65 Ontos in
If this figure is correct it may have represented 45
Ontos of the 3rd Marine Anti-Tanks and a lesser number from the 1st
Marine Anti-Tanks; as some of the machines were aboard ships in a
standby mode awaiting to be deployed in any hot spots that arose.
The Ontos crew
carried 6 of the 106MM rounds in their guns. They carried 8 shells
in the rear storage area under the rear doors and 4 rounds in a rack
located in the right rear of the vehicle. The loader would
dismount and reload from this ammo locker. The interior of the
vehicle may carry additional shells depending on the situation. I
interviewed an Ontos platoon Sgt. that removed both the driver's seat
and commander's seat and piled
30 additional shells
into the cramped
space. He sat on the ammo while driving or firing the weapons.
The crew also
carried an M-3A1 submachine gun (also known as the grease gun or SMG)
and Colt 45 automatic pistol (worn in a shoulder holster) with 250
rounds, 1,000 tracer rounds for the 50 calibre M8 spotting rifles, and
1,000 or more rounds for the 1919A4 Browning machine gun. Many of
the crewmen carried personal weapons.
Some of the personal weapons
included shotguns and captured weapons such as the Thompson submachine
gun, AK-47 and SKS communist made rifles as well as the French made
submachine guns. One crew, known to me, also mounted a 60MM mortar
on the front plates of the Ontos.
The Marine Infantry
Battalions were armed with the M60 machine gun during this period.
For some unknown reason, the Ontos continued to carry the older light
Browning machine gun. Some of the crews had the option of changing
to the more modern, fully automatic weapon, but opted for the Browning.
The older Browning had a reputation to require fewer barrel changes from
heavy use. The Browning machine gun was mounted on a pipe support
attached to the gun mount/turret. It could be fired manually or
remotely from inside the Ontos by way of a foot pedal.
happened to the Ontos?
deactivated the Ontos from Vietnam in May 1969. A few of the
Ontos were left in Vietnam and turned over to an Army Light Infantry
Brigade near Tam KY. The Army ran them until they ran out of
replacement parts. They then made them into fixed bunkers.
The remainder of the machines in Vietnam were loaded into ships in May
of 1969 for return to the US. The crews were reassigned to various
Marine Infantry Battalions.
Once the machines
were returned to the US, their top hulls were cut off and many of the
chassis were sold for construction equipment or given to local
governmental agencies for rescue work. http://ontos.homestead.com/ms3.html