The Ontos was a lightweight tracked armored fighting vehicle, designed in the early 1950's to be an air transportable tank destroyer capable of being
transported by the current cargo aircraft. Its mission was to destroy the main battle tanks of this era using the firepower from its six 106mm recoilless
rifles.
The contract was awarded to Allis-Chamlers and, amazingly, only contained one page of specifications. These specifications demanded that the
vehicle should be powered by the GMC six cylinder Model 302 petrol engine, standard for the 2½ton military trucks in use then, and
a front-mounted Allison XT-92-2 cross drive transmission that would carry power to the tracks. The remainder of the specifications restricted the outside dimensions
and weight so that the vehicle would be air transportable. Much of the engineering work was completed in 1950 during a two-week design marathon and
all the prototypes were constructed in the Agricultural Assembly Plant in LaPort, Indiana. The government would only accept the prototypes for testing
after they had accumulated 50 hours of running time so this meant Allis-Chamlers employees had to come to the plant on weekends and drive the
prototypes around the factory grounds until the required number of hours had accumulated. The Ontos concept began with the T55 & T56. It then
went to the T164, T165, T166, T167. The T165 was chosen for further testing and it became the T165E1 and then the T165E2. This is what became the M50.
The contract was originally for 1000 vehicles to be delivered to the Army. But in 1953, the army refused to accept delivery of the Ontos. At this point the
USMC stepped in and accepted delivery of about 300 vehicles but they continued to test the vehicles for the next three years until they were finally
accepted in late 1956.
The general design of the vehicles in the series was with the engine on the front right with the transmission in front of it. A rubber bladder-type fuel tank with a capacity of 47
gallons was mounted in the front of the vehicle directly behind the glacis plate. It was moulded in rubber and contained a cylindrical tube through its center to allow
the drive-shaft to pass through the fuel tank on its way to the left hand drive sprocket.
The glacis plate was 1" thick and protected the driver and transmission. The side plates that held the track suspension parts
and formed the sides of the crew compartment were slightly thicker than ½". The floor of the fighting compartment was constructed of ¼"
thick steel plate. The majority of the remainder of the hull was formed from ½" thick armor plate. The engine decks were cast of armored steel with
each louvre having a ½" bead on the inside lip to prevent SA fire and fragments from entering the engine compartment. The double doors on the
sloping hull rear plate were the normal method of entry/exit for the crew.
The suspension system was designed so that nothing intruded into the interior of the fighting compartment. The road wheels hung on torsion bushings
that were attached to the sides of the hull.
Each track consisted of two sections of rubber; 48" long with steel drive teeth in the center. 20" wide steel grousers held the rubber and the drive teeth
together. It took 5 sections of track to make up a complete track and a crew could replace a track section in about 1½ hours.
The vehicle had a range of 150 miles at 30mph. It could climb 60° slopes and was capable of fording 24" of water, It could also climb a 30" step and
cross a 56" ditch.
