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M50
M50A1

Multiple 106mm Self-propelled Rifle M501-5

M50: General
Date of first acceptance October 1956 Total acceptances 297
Manufacturer Allis-Chalmers Manufacturing Co. Crew
3 men:
  • Commander/gunner in hull center rear
  • Driver in hull left front
  • Loader in hull center rear
M50: Dimensions*
Combat weight 19,050lbs
8641kg
Height 83.9"
213cm
Length 150.8"
383.0cm
Width over fenders 102.3"
259.8cm
Tread 73.0"
185cm
Ground clearance 14.6"
37.1cm
Fire height, top rifles ~78"
~200cm
Turret ring diameter 31.7"
80.5cm
Ground pressure, zero penetration 5.1psi
.36kg/cm²
M50: Armament
Type Mount Ammunition Traverse Elevation
Six 106mm Recoilless Rifles M40A1C T149E5 on turret 18 rounds 80°
(40° left and right;
manual)
+20° to -10°
(manual)
.30cal M1919A4 MG Fixed or flexible in turret mount 1000 rounds 360°
(Manual)
Manual
Rangefinder
Four .50cal Spotting Rifles M8C on top of 106mm rifles;
80 rounds .50cal
M50: Armor
Assembly
Welding
Hull
Rolled homogeneous steel
Location Thickness Angle from vertical
Upper front .5"
1.3cm
71°
Lower front .5"
1.3cm
45°
Upper sides .5"
1.3cm
42°
Lower sides .5"
1.3cm
Upper rear .5"
1.3cm
27°
Lower rear .5"
1.3cm
Top .5"
1.3cm
90°
Floor .25"
.64cm
90°
Turret
Rolled homogeneous steel
Location Thickness Angle from vertical
Front .5"
1.3cm
30°
Sides .5"
1.3cm
30°
Rear .5"
1.3cm
30°
Top .5"
1.3cm
90°
M50: Automotive
Engine General Motors Model 302; 6 cylinder, 4 cycle, in-line gasoline
Horsepower Net: 124@2400rpm
Gross: 145@3400rpm
Torque Net: 252 ft-lb@1400rpm
Gross: 255 ft-lb@2000rpm
Fuel capacity 47gal
180L
Transmission Allison X-drive XT-90-2, 3 ranges forward, 1 reverse
Steering Mechanical clutch-brake, steering levers
Brakes Multiple disc
M50: Suspension
Type Road wheels Track return rollers
Torsilastic 4 individually sprung dual/track 4 track skid bumpers/track
Drive sprockets Idlers Shock absorbers
15-tooth front drive Rear road wheels serve as adjustable trailing idlers On first, second, and third road wheels/track
M50: Track
T123
Center and outside guide band type
Width 20"
51cm
Pitch 60" long sections;
4" crossbar pitch
150cm long sections;
10cm crossbar pitch
Shoes/track 5 sections/track;
75 crossbars/track
Ground contact length 94.2"
239cm
M50: Performance
Max level road speed 30mph
48kph
Max trench 54"
140cm
Max grade 60% Max vertical obstacle 28"
71cm
Min turning diameter 18'
5.5m
Max fording depth 24"
61cm
Cruising range ~115mi, roads
~185km, roads

The M50, known as the Ontos, mounted six recoilless rifles, 3 per side, on a small turret atop its pyramid-like hull. The rifles were actually 105mm in diameter, but were dubbed 106mm rifles to prevent confusion with earlier 105mm rifles. The .50cal spotting rifles were mounted on top of the upper 106mm weapons, and the .30cal MG mount was in the center on the turret roof. The rifles were numbered 1 through 6 clockwise starting with the bottom left rifle when looking at them from behind the vehicle; although any rifle could be quickly dismounted for ground use, rifles 2 and 5 were specifically designated for this and consequently their spotting rifles were not used when mounted on the vehicle. The spotting rifles were ballistically matched to 1100 yards (1000m) and could be used to 1500 yards (1400m), beyond which burst on target was the preferred spotting method. The rifles could be fired singly or in combination up to all six at once. The suggested single firing order was rifle 1, 6, 2, 5, 3, 4 in order to maintain the maximum two-rifle salvos at all times, and the recommended two-rifle firing order was rifles 1 and 6, 2 and 5, and 3 and 4 in order to maintain turret balance. Crew access included a driver's hatch in the front of the vehicle and double doors in the rear for the gunner and loader. Besides the six 106mm rounds stored in the loaded rifles, there was an eight-round ammunition compartment in the vehicle's bottom rear, and four more rounds were stowed in the right rear of the gunner's compartment. The 106mm rifles could only be loaded from outside the vehicle.

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Multiple 106mm Self-propelled Rifle M50A11-2,6-8

M50A1: General
Date of first acceptance 1963
Manufacturer Allis-Chalmers Manufacturing Co. Crew
3 men:
  • Commander/gunner in hull center rear
  • Driver in hull left front
  • Loader in hull center rear
M50A1: Dimensions*
Weight 19,050lbs
8641kg
Height 86"
220cm
Length 151"
384cm
Width 102.25"
259.72cm
Tread 73.0"
185cm
Ground clearance 14.625"
37.148cm
Fire height, top rifles ~78"
~200cm
Turret ring diameter 31.7"
80.5cm
Unit ground pressure 4.7psi
.33kg.cm²
M50A1: Armament
Type Mount Ammunition Traverse Elevation
Six 106mm Recoilless Rifles M40A1C T149E5 on turret 18 rounds 80°
(40° left and right;
manual)
+20° to -10°
(manual)
.30cal M1919A4 MG Fixed or flexible in turret mount 1000 rounds 360°
(Manual)
Manual
Rangefinder
Four .50cal Spotting Rifles M8C on top of 106mm rifles;
80 rounds .50cal
M50A1: Armor
Assembly
Welding
Hull
Rolled homogeneous steel
Location Thickness Angle from vertical
Upper front .5"
1.3cm
71°
Lower front .5"
1.3cm
45°
Upper sides .5"
1.3cm
42°
Lower sides .5"
1.3cm
Upper rear .5"
1.3cm
27°
Lower rear .5"
1.3cm
Top .5"
1.3cm
90°
Floor .25"
.64cm
90°
Turret
Rolled homogeneous steel
Location Thickness Angle from vertical
Front .5"
1.3cm
30°
Sides .5"
1.3cm
30°
Rear .5"
1.3cm
30°
Top .5"
1.3cm
90°
M50A1: Automotive
Engine Chrysler HT-361-318; 8 cylinder, 4 cycle, vee gasoline
Horsepower Gross: 180@3450rpm Torque Gross: 283 ft-lb@2400rpm Fuel capacity 47gal
180L
Transmission Allison X-drive XT-90-5, 3 ranges forward, 1 reverse
Steering Mechanical clutch-brake, steering levers
Brakes Multiple disc
M50A1: Suspension
Type Road wheels Track return rollers
Torsilastic 4 individually sprung dual/track 4 track skid bumpers/track
Drive sprockets Idlers Shock absorbers
15-tooth front drive Rear road wheels serve as adjustable trailing idlers On first, second, and third road wheels/track
M50A1: Track
T123
Center and outside guide band type
Width 20"
51cm
Pitch 60" long sections;
4" crossbar pitch
150cm long sections;
10cm crossbar pitch
Shoes/track 5 sections/track;
75 crossbars/track
Ground contact length 94.1875"
239.236cm
M50A1: Performance
Max level road speed 30mph
48kph
Max trench 54"
140cm
Max grade 60% Max vertical obstacle 28"
71cm
Min turning diameter 18'
5.5m
Max fording depth 24"
61cm
Cruising range ~125mi, roads
~200km, roads

The M50A1 got a new engine and transmission, and can be differentiated from M50 by the additional cooling louvres on the engine and transmission access doors as well as above the engine compartment to the right of the driver.

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References

  1. Hunnicutt, R.P. Sheridan: A History of the American Light Tank, volume 2. Navato, CA: Presidio Press, 1995. Reprinted with permission from Sheridan, R.P. Hunnicutt ©1995, available from Presidio Press, 505B San Martin Drive, Suite 160, Navato, CA 94945.
  2. Estes, Kenneth W. M50 Ontos and M56 Scorpion 1956-1970: US Tank Destroyers of the Vietnam War. Oxford: Osprey Publishing Ltd., 2016.
  3. MICO P1550.228 The Ontos. Washington, DC: Marine Corps Institute, 12 Mar 1962.
  4. Crismon, Fred W. U.S. Military Tracked Vehicles. Osceola, WI: Motorbooks International, 1992.
  5. LFB-23 Employment of the Antitank Battalion. Washington, DC: Headquarters, US Marine Corps, 23 Dec 1959.
  6. TM-00545B-10 Rifle, Self-propelled, Full-tracked, Multiple 106mm, M50A1 Operation and First-echelon Maintenance. Washington, DC: Headquarters, US Marine Corps, 30 Dec 1963.
  7. TM-00545B-35/1 Rifle, Self-propelled, Full-tracked, Multiple 106mm, M50A1 Field and Depot Maintenance. Washington, DC: Headquarters, US Marine Corps, 15 Jan 1964.
  8. Estes, Kenneth W. Marines Under Armor. Annapolis, MD: Naval Institute Press, 2000.

*The dimensional table for the M50 was compiled from information reprinted with permission from Hunnicutt's Sheridan. That for the M50A1 was compiled from TM-00545B-10. Any inconsistencies should presumably simply be chalked up to differences in source data and not to actual differences in production.


Last updated 17 Apr 2021.
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