USA M50 Ontos tank destroyer Armoured Vehicles of the 1950s and 1960s In the early 1950s the US Marine Corps issued a requirement for a highly mobile tank destroyer and in October 1951 authorization was forgiven the building of no less than five prototype vehicles all of which had various numbers of recoilless rifles as their main armament These were built and tested and in February 1953 approval was forgiven the procurement of 24 models of the T165 which was armed with six 106-mm recoilless rifles. Trials with the first of these vehicles showed that some work was required with the mounting fire-control system and suspension. The remaining vehicles were built to a slightly modified design and designated the T165E2. Following trials with the latter vehicles and more modifications the vehicle was finally accepted for service with the US Marine Corps and in 1955 was standardized as the Rifle Multiple 106-mm Self-Propelled M50 or as it was normally called the Ontos (Greek for The Thing). In August 1955 Allis Chalmers was awarded a production contract for 297 vehicles which were all completed by November 1957 At a later date it was decided to replace the original General Motors petrol engine with a Chrysler petrol engine developing 180 hp (134 kW) and subsequently, in June 1963 the original manufacturer was awarded a contract to rebuild 294 M50 vehicles to the new configuration known as M50A1 at the same time a number of other minor improvements were made to the vehicle The M50 was used in South Vietnam and in the Dominican Republic but it has now been retired from service with the US Marine Corps without a direct replacement although ground- and vehicle-mounted TOW ATGWs carryout a similar function. The vehicle was armed with six M40A1C recoilless rifles mounted on a common mount at the rear of the hull. These had a traverse of 40° left and right with an elevation of +20° and a depression of -10° elevation and traverse all being manual. The top four recoilless rifles were fitted with a 12.7- mm 5-in) (0 M8C spotting rifle: the weapons were first lined up with the optical sight and the spotting rifle was then fired a hit on the target being indicated by a puff of smoke whereupon the gunner knew that the recoilless rifle was correctly aligned with the target. One or more of the recoilless rifles could be fired maximum effective range being about 1100m (1,200 yards) although maximum range was over 7000 m (7655 yards). The ammunition was of the fixed type and included HEAT (High Explosive Anti-Tank) and HEP-T (High Explosive Plastic-Tracer) the latter type being known as HESH in British service. Totals of 1 8 rounds of 106-mm and 80 rounds of spotting ammunition were carried. In addition an M1919A4 7.62 -mm (0.3-in) machine-gun was fitted to the top of the mount for local protection. The driver was seated at the front of the hull on the left with the engine to his right and the very cramped crew compartment at the rear entry to the latter was effected via two indoors the hull rear. The engine was coupled to a General Motors Corporation (Allison Division) X T -90-2 cross drive transmission that transmitted power to the drive sprockets at the front of the hull. The chassis was also used for a number of experimental vehicles but none of these including several armoured/ infantry carriers entered production or service. Specification Crew: 3 Weight: 864 tonnes Dimensions: length 3.82 m (12 ft 6% in) width 260 m (8 ft 6!/4 in) height 213 m M50 On tos tank destroyer as used by the US Marine Corps. Note the 12.7- mm spottingMGs above the top four 106-mm recoilless rifles. Once these had been fired the crew had to leave the vehicle to reload them. (6 ft 11% in) Powerplant: one General Motors Corporation Model 302 petrol engine developing 145 hp (108 kW) Performance: maximum road speed 48 km/h (30 mph) maximum road range 240 km (150 miles) gradient 60 percent vertical obstacle 0.76 m (30 in)trench 1.42 m (4 ft 8 in) «¦If m m M56 90-mm airborne self-propelled anti-tank gun Apart from hand-held weapons the most important anti-tank weapon used by US airborne forces in World War II was the jeep-towed 57-mm anti-tank gun Ml which was essentially the British 6-pdr made in the United States, After the war a requirement was issued for a highly mobile self- propelled anti-tank gun that could be air-dropped by parachute during the initial phases of airborne operations and have a firepower similar to that of a tank Two prototypes of a vehicle called the T101 were built by the Cadillac MotorCar Division of the General Motors Corporation. Further development resulted in the improved T101E1 which was eventually standardized as the Gun Anti-tank Self-propelled 90- nun M56 or more commonly the Scorpion. Production was undertaken by the Cadillac MotorCar Division between 1953 and 1959 .In the US Army the M56 was issued only to the 82nd and 101st Airborne Divisions but was replaced in the 1960s by theM 551 Sheridan Armored Reconnaissance/ Airborne Assault Vehicle A few M56s were supplied to Spain and Morocco, and some were also deployed by the US Army to Vietnam where they were used mainly in the fire-support role. The hull of the M56 was of all welded and riveted aluminium construction, with the engine and transmission at the front gun in the centre and the crew area at the rear The engine was coupled to a General Motors Corporation (Allison Division) transmission with one reverse and two forward ranges which in turn supplied power to the final drives on each side. The suspen- MS6 90-mm self-propelled anti-tank gun which was often called the Scorpion. This was developed specifically for the US 82nd and 101st Airborne Divisions. Its main drawback apart from the recoil when the 90-mm gun was fired was the complete lack of armour protection for the stun crew apart from the small shield. A total of 29 rounds of fixed 90-mm ammunition was carried for the gun which had a maximum effective range of about 1500 m (4920 ft). sion was of the torsion-bar type with four rubber-tyred road wheels idler at the rear and drive sprocket at the front there were no track-return rollers The track consisted of a steel-reinforced endless rubber-band The main armament was a 90-mm gun M54 fitted with a muzzle brake and a vertical sliding breech block. The gun had an elevation of +15° and depression of -10° and a traverse of 30° left and right all manual. A total of 29 rounds of fixed ammunition was car- One of the prototypes of theM56, then designated the T101 shortly after the 90-mm gun had tired, showing the gun recoilling to the rear and the forward part of the chassis lifting clear of the ground. The dust often obscured the gunner's line of sight for the next shot. w 243
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