75mm Howitzer Motor Carriage M81-5
M8: General
Date of introduction September 1942 Total acceptances 1778
Manufacturer Cadillac Motor Car Division of General Motors Crew
4 men:
  • Chief of section in turret right rear
  • Corporal gunner in turret right
  • Loader in turret left
  • Driver in hull left front
M8: Dimensions
Combat weight 34,600lbs
15,700kg
Height over AAMG 107"
272cm
Length with sandshields 196"
498cm
Howitzer overhang forward 0"
Width with sandshields 91.5"
232cm
Tread 73.5"
187cm
Ground clearance 14"
36cm
Fire height 76"
190cm
Turret ring diameter 54.4"
138cm
Ground pressure, zero penetration 12.5psi
.878kg/cm²
M8: Armament
Type Mount Ammunition Traverse Elevation
75mm Howitzer M2 or M3 M7 in turret 46 rounds
(6 ready)
360°
(manual)
+40° to -20°
(manual)
.50cal M2HB MG Ring mount in turret 400 rounds 360°
(manual)
Manual
M8: Armor
Assembly
Welding
Hull
Rolled homogeneous steel
Location Thickness Angle from vertical
Upper front 1.125"
2.858cm
45°
Lower front 1.75"
4.45cm
18°
Front sides 1.125"
2.858cm
Rear sides 1.0"
2.5cm
Upper rear 1.0"
2.5cm
50°
Middle rear 1.0"
2.5cm
Lower rear 1.0"
2.5cm
17°
Top .5"
1.3cm
90°
Front floor .5"
1.3cm
90°
Rear floor .375"
.953cm
90°
Turret
Rolled homogeneous steel
Location Thickness Angle from vertical
Howitzer shield (cast) 1.5"
3.8cm
0° to 60°
Front 1.5"
3.8cm
0° to 63°
Sides 1.0"
2.5cm
20°
Rear 1.0"
2.5cm
20°
Top Open
M8: Automotive
Engine Twin Cadillac Series 42; 16 cylinder (8/engine), 4 cycle, 90 vee gasoline
Horsepower Net: 220@3400rpm
(110/engine)
Gross: 295@3200rpm
(148/engine)
Torque Net: 488 ft-lb@1200rpm
(244/engine)
Gross: 560 ft-lb@
1200rpm (260/engine)
Fuel capacity 89gal
340L
Transmission Twin Hydramatic, 4 speeds forward, 1 reverse
Steering Controlled differential, steering levers
Brakes Mechanical, external contracting
M8: Suspension
Type Road wheels Track return rollers
Vertical volute spring 2 bogies/track;
2 wheels/bogie
3/track
Drive sprockets Idlers Shock absorbers
13-tooth front drive Trailing adjustable with volute spring at rear of track None
M8: Track
T16E1
Outside guide, rubber bushed, double pin, reversible rubber
Width 11.6"
29.5cm
Pitch 5.5"
14cm
Shoes/track 66 Ground contact length 119"
302cm
T16E2
Outside guide, rubber bushed, double pin, non-reversible rubber
Width 11.6"
29.5cm
Pitch 5.5"
14cm
Shoes/track 66 Ground contact length 119"
302cm
T36E6
Outside guide, rubber bushed, double pin, steel, parallel grouser
Width 11.6"
29.5cm
Pitch 5.5"
14cm
Shoes/track 66 Ground contact length 119"
302cm
T55E1
Outside guide, rubber bushed, double pin, steel, chevron
Width 11.6"
29.5cm
Pitch 5.5"
14cm
Shoes/track 66 Ground contact length 119"
302cm
M8: Performance
Max level road speed 36mph
58kph
Max trench 64"
160cm
Max grade 60% Max vertical obstacle 18"
46cm
Min turning diameter 42'
13m
Max fording depth 36"
91cm
Cruising range ~100mi, roads
~160km, roads


The 75mm HMC M8 was based on the light tank M5, but the front hull was modified by deletion of the drivers' hull roof hatches since the drivers had access to the vehicle through the open turret. Instead, the drivers each had a large door in the hull front plate for direct vision and two periscopes in the hull roof. The M7 howitzer mount incorporated parts of the medium tank M4's M34 gun mount. The 75mm howitzer M3 differed from the M2 by having the recoil surface and keyway machined directly onto the howitzer tube and therefore not requiring a barrel support sleeve. Both howitzers used the same breech, and a large flash suppressor was fitted around the howitzer on the M8. Late-model M8s were armed with the M3 howitzer, equipped with sandshields around the tracks, and they stored track grousers on the turret.

The mounted positions of the crew differed from the action positions listed above. For travel, the chief rode in right side of the turret, the loader occupied the .50cal ring mount, and the gunner sat in the assistant driver's position.


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References

  1. TM 9-732B 75-mm Howitzer Motor Carriage M8. Washington, DC: War Department, 31 January 1944.

  2. Hunnicutt, R.P. Stuart: A History of the American Light Tank, volume 1. Navato, CA: Presidio Press, 1992.
    Reprinted with permission from Stuart, R.P. Hunnicutt ©1992, available from Presidio Press, 505B San Martin Drive, Suite 160, Navato, CA 94945.

  3. FM 17-69 Crew Drill, Service of the Piece, and Gunnery (75-mm Assault Howitzer on Motor Carriage M8). Washington, DC: War Department, 30 November 1943.

  4. Chamberlain, Peter, and Chris Ellis. British and American Tanks of World War Two. Frome, England: Cassell & Co., 2000.

  5. Siemers, Cary. "USA's Self Propelled Guns." World War II Tanks & Vehicles and Advanced Squad Leader. 25 Nov 2000. 24 Jan 2001 <http://www.shadowsfolly.com/WWII/USA/SelfPropelled.htm>.



Last updated 20 Aug 2013.

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