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M4
M4A1

81mm Mortar Carrier M4, early production1-12

M4: General
Date of first acceptance August 1941 Total acceptances 572
Manufacturer White Motor Co. Crew 6 men
M4: Dimensions
Combat weight 17,350lbs
7,970kg		 Height 89.375"
227.01cm
Length with roller 236.75"
601.35cm		 Width over side armor 77.25"
196.2cm
Front tread 64.5"
164cm		 Rear tread 63.8"
162cm
Wheelbase 135.5"
344.2cm		 Ground clearance 11.2"
28.4cm
Ground pressure, tires 29.8psi
2.09kg/cm²
M4: Armament
Type Mount Ammunition Traverse Elevation
81mm Mortar M1 Mount M1 96 rounds 130 mils
(65 mils left and 65 mils right;
manual)		 +80° to +40°
(manual)
.30cal M1919A4 MG Flexible on skate mount M29, M30, M35, or M35C 2,000 rounds 360°
(manual)		 +35° to -25°
(manual)
Aiming equipment
Sight M6 for gunner
M4: Armor
Assembly
Bolting
Hull
Rolled face-hardened steel
Location Thickness Angle from vertical
Radiator louvres .25"
.64cm		 26°
Windshield cover .50"
1.3cm		 25°
Sides .25"
.64cm		 0°
Rear .25"
.64cm		 0°
Hood top .25"
.64cm		 83°
M4: Automotive
Engine White 160AX; 6 cylinder, 4 cycle, in-line gasoline
Horsepower Net: 147@3,000rpm Torque Net: 325 ft-lb@1,200rpm Fuel capacity 60gal
230L
Transmission Spicer 3461 constant mesh, 4 speeds forward, 1 reverse
Steering Steering wheel
Brakes Hydraulic (Hydrovac)
M4: Suspension
Type Road wheels Track return rollers
Front: Semi-elliptic longitudinal leaf spring
Rear: Vertical volute spring		 Front: Steel ventilated disc
Rear: 1 bogie/track;
4 dual/bogie		 1 dual/track
Drive sprockets Idlers Shock absorbers
18-tooth front drive Adjustable fixed at rear of track On front wheels
M4: Track
T68E1
Center guide band type
Width 12"
30cm		 Pitch 4"
10cm		 Pitches/track 58 Track ground contact length 46.75"
118.7cm
M4: Performance
Max level road speed 45mph
72kph		 Max grade 60%
Angle of approach 37° Angle of departure 45°
Max vertical obstacle 12"
30cm		 Min turning diameter 59'
18m
Max fording depth 32"
81cm		 Cruising range ~200mi, roads
~320km, roads

The M4 mortar carrier was based on the half-track car M2, and the mortar was placed in the rear compartment and pointed rearwards. The side ammunition compartments were retained, and additional 81mm mortar bomb stowage compartments were placed behind the standard stowage boxes. A rear door was installed on the M4, but the machine gun skate mount was retained, forcing crewmen to crawl under the skate rail if they wanted to use the rear door. The mortar was intended to be fired from the ground except for emergency situations, so the vehicle mortar mount was very limited in traverse.

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81mm Mortar Carrier M4A11-11

M4A1: General
Date of first acceptance May 1943 Total acceptances 600
Manufacturer White Motor Co. Crew 6 men
M4A1: Dimensions
Combat weight 18,000lbs
8,200kg		 Height 89.375"
227.01cm
Length with winch 243.625"
618.808cm		 Width over side armor 77.25"
196.2cm
Front tread 64.5"
164cm		 Rear tread 63.8"
162cm
Wheelbase 135.5"
344.2cm		 Ground clearance 11.2"
28.4cm
Ground pressure, tires 29.8psi
2.09kg/cm²
M4A1: Armament
Type Mount Ammunition Traverse Elevation
81mm Mortar M1 Mount M1 96 rounds 600 mils
(manual)		 +80° to +40°
(manual)
.30cal M1919A4 MG Flexible on skate mount M29, M35, or M35C 2,000 rounds 360°
(manual)		 +35° to -25°
(manual)
Aiming equipment
Sight M6 for gunner
M4A1: Armor
Assembly
Bolting
Hull
Rolled face-hardened steel
Location Thickness Angle from vertical
Radiator louvres .25"
.64cm		 26°
Windshield cover .50"
1.3cm		 25°
Sides .25"
.64cm		 0°
Rear .25"
.64cm		 0°
Hood top .25"
.64cm		 83°
M4A1: Automotive
Engine White 160AX; 6 cylinder, 4 cycle, in-line gasoline
Horsepower Net: 147@3,000rpm Torque Net: 325 ft-lb@1,200rpm Fuel capacity 60gal
230L
Transmission Spicer 3461 constant mesh, 4 speeds forward, 1 reverse
Steering Steering wheel
Brakes Hydraulic (Hydrovac)
M4A1: Suspension
Type Road wheels Track return rollers
Front: Semi-elliptic longitudinal leaf spring
Rear: Vertical volute spring		 Front: Steel ventilated disc
Rear: 1 bogie/track;
4 dual/bogie		 1 dual/track
Drive sprockets Idlers Shock absorbers
18-tooth front drive Spring-loaded at rear of track On front wheels
M4A1: Track
T68E1
Center guide band type
Width 12"
30cm		 Pitch 4"
10cm		 Pitches/track 58 Track ground contact length 46.75"
118.7cm
M4A1: Performance
Max level road speed 45mph
72kph		 Max grade 60%
Angle of approach 33° Angle of departure 45°
Max vertical obstacle 12"
30cm		 Min turning diameter 59'
18m
Max fording depth 32"
81cm		 Cruising range ~200mi, roads
~320km, roads

The limited traverse mount of the M4 was unacceptable once it was realized that it was desirable to fire the mortar mounted on the carrier. The M4A1 incorporated a new rough traverse mechanism that allowed 600 mils of traverse in 100-mil increments, but fine adjustments were still made with the mortar's bipod mount. To accommodate the rough traverse feature, the mortar socket was elevated 7.375" (18.73cm) and the rear mortar bomb ammunition racks were removed. Ammunition stowage remained at 96, however. The M4A1 also featured stowage boxes mounted on the outside of the rear plate, on either side of the access door.

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References

  1. Hunnicutt, R.P. Half-Track: A History of American Semi-tracked Vehicles. Navato, CA: Presidio Press, 2001. Reprinted from Half-Track, R.P. Hunnicutt ©2001, available from Presidio Press, 505B San Martin Drive, Suite 160, Navato, CA 94945.
  2. Doyle, David. U.S. Half-tracks: The Development and Deployment of the U.S. Army's Half-track Based Multiple Gun Motor Carriages and Gun Motor Carriages, Part two. Ed. Pat Stansell. Delray Beach, FL: The Ampersand Publishing Group, Inc., 2016.
  3. TM 9-710 Basic Half-Track Vehicles (White, Autocar, and Diamond T). Washington, DC: War Department, 23 February 1944.
  4. TM 9-710/TO 19-75A-77 Half-track Vehicles Car M2A1; Personnel Carrier M3 and M3A1; 81-mm Mortar Carrier M4, M4A1, and M21; Combination Gun Motor Carriage M15A1; and Multiple Gun Motor Carriage M16 and M16A1. Washington, DC: Departments of the Army and the Air Force, 8 May 1953.
  5. Crismon, Fred W. U.S. Military Tracked Vehicles. Osceola, WI: Motorbooks International, 1992.
  6. TM 9-2800 Standard Military Motor Vehicles. Washington, DC: War Dept., 1 Sep 1943.
  7. Sola, Samuel, Vincent Bobkowski, and Kara Crocker. Weapon Mounts for Secondary Armament. Santa Monica, CA: G. O. Noville & Associates, Inc., April 1957.
  8. Chamberlain, Peter, and Chris Ellis. British and American Tanks of World War Two. Frome, England: Cassell & Co., 2000.
  9. Hogg, Ian V. The Greenhill Armoured Fighting Vehicles Data Book. London: Greenhill Books, 2000.
  10. Siemers, Cary. "USA's Half Track Gun Motor/Mortar Carriages." World War II Tanks & Vehicles and Advanced Squad Leader. 4 Jul 2001. 11 Aug 2001 <http://www.siemers.com/wwii/USA/GunMotorCarriage.htm>.
  11. Track Data. Warren, MI: Track & Suspension Laboratory, Components Research and Development Laboratories, Research & Engineering Directorate, US Army Tank-Automotive Center, 23 June 1965.
  12. Tank Data, vol. 2. Aberdeen Proving Ground, MD: US Army Ordnance School, Jul 1958.
Last updated 8 Jan 2024.
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© Copyright 2001-24 Chris Conners