4.2" Mortar Motor Carriage M21-3

M2: General
Manufacturer White Motor Co. Total acceptances 6
Crew 5 men
M2: Dimensions
Weight, net, equipped 7,670lbs
Height 81"
Length 202.50"
Width 80.37"
Front tread 63.75"
Rear tread 63.75"
Wheelbase 131"
Ground clearance 9.75"
Ground pressure 57psi
M2: Armament
Type Mount Traverse Elevation
4.2" Chemical Mortar M1A1 Mount in rear compartment Manual +45° to +60°
.30cal M1919A4 MG Flexible on pedestal mount T34 360°
M2: Armor
Location Thickness
Windshield .50"
Other surfaces .25"
M2: Automotive
Engine Hercules JXD; 6 cylinder, 4 cycle, in-line gasoline
Horsepower 95@3000rpm Torque 224 ft-lb@1100rpm Fuel capacity 26.5gal
Transmission Clark Equipment Co. Model 230-F combination sliding and constant mesh, 4 speeds forward, 1 reverse
Steering Ross Gear and Tool Co. Type 660 cam and lever type, steering wheel
Brakes Hydraulic, internal expanding
M2: Suspension
Type Road wheels Shock absorbers
Semi-elliptic leaf spring 2/side On each wheel
M2: Performance
Max level road speed 55mph
Min turning diameter 29.25'
Angle of approach 37° Angle of departure 35°
Max fording depth 22.50"

The 4.2" mortar motor carriage M2 was based on the scout car M3. The machine gun skate rail was removed from the rear compartment, and the mortar mount was emplaced centrally. The mortar could be detached from the vehicle for firing. When dismounted, elevation from 45° to 60° was achievable, and when fired while attached to the carrier, 60° of elevation was possible. An ammunition rack for the mortar was installed behind the 3-man driver's compartment, and two seats were retained in the rear for the gun crew. The rear seats needed to be removed to access the mortar ammunition. The machine gun was installed on a pedestal mount on the passenger running board behind the front fender.

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  1. Hunnicutt, R.P. Armored Car: A History of American Wheeled Combat Vehicles. Novato, CA: Presidio Press, 2002. Reprinted from Armored Car, R.P. Hunnicutt ©2002, available from Presidio Press, 505B San Martin Drive, Suite 160, Novato, CA 94945.
  2. TM 9-705 Scout Cars, M3, M3A1, and 4.2 Mortar Motor Carriage, M2. Washington, DC: War Department, 19 February 1941.
  3. 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.

Last updated 7 Oct 2021.
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