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United States' M12 Gun Motor Carriage
Nickname: door knocker

Photos

M12 Gun Motor Carriage:
United States' M12 Gun Motor Carriage
Aberdeen Tank Museum

Design

The Chief of Ordnance ordered a pilot model to have a 155 mm M1918M1 gun put onto a M3 medium chassis. This was designated the T6 and work began on it in June 1941.

Engine

The engine was located in the front of the M12.

Crew

The vehicle commander and driver sat in a compartment at the front of the M12.

The driver and assistant driver had direct and indirect vision. In the M12 there were seats for 4 other crewmen. There was also a hinged platform for the crew for firing.

The M12 provided armor protection for the crew.

Main Armament

The 155 mm M1918 was formerly a French gun that was used as towed artillery in World War I. After World War I they were placed into storage.

The 155 mm gun fired a 95 lb shell at a muzzle velocity of 2,380'/sec and a range of 18,000 yards.

Firing Spade

The M12 had a spade at the rear to help stabilize against the recoil of the gun. This could be raised when moving.

Prototype

The T6 prototype was manufactured by Rock Island Arsenal. Pressed Steel Car Company fitted French M1917 or US made M1918 guns.

The T6 prototype started testing at the Aberdeen Proving Ground in February 1942. It had some modification done and was sent to Fort Bragg for the Field Artillery Board to test. The T6 proved acceptable, except to the Army Ground Forces, who felt towed artillery was good enough.

During tests the T6 was fired, moved six miles, and then fired again. This took a total of 35 minutes to complete. A tractor towed 155 mm gun required three hours to do the same thing. The Ordnance Board ordered 50 initially, which was increased to 100.

Production

Initial production of 100 of the M12 and M30 were completed in March 1943 by Pressed Steel Car Company. These were stored or used for training.

When the Normandy landings was getting closer it was decided to remanufacture them. Baldwin Locomotive Works rebuilt 74 of them by May 1944 with the M4 chassis.

  • M12 Gun Motor Carriage:
    • Manufactured by: Pressed Steel Car Company
  • M30 Cargo Carrier:
    • Manufactured by: Pressed Steel Car Company
  • Total: 100
    • Production: late 1943 - March 1944

Variants

  • M12 Gun Motor Carriage:
  • M30 Cargo Carrier: Identical to M12 except no gun. There was on M30 for each M12. The crew primarily traveled in the M30. There was a tailgate to help unload the ammunition. A ring mount for a .50 cal MG was installed in the rear. There was a canvas cover over the crew area.

Usage

Eventually 74 were sent to Europe in June 1944. They were used in the taking of Cologne and in busting the bunkers in the Siegfried Line.

Used in Italy, France, and Germany.

Specifications

  M12 Gun Motor Carriage
Crew Commander, driver, gun crew (4)
5, 6
Physical Characteristics  
Weight 58,000 lb
26.3 tons, 27.1 tons, 29 tons
26,762 kg, 29,464 kg
Length 22.1', 22' 1", 22' 3"
6.67 m, 6.73 m
Height 8.8', 8' 10", 9' 6"
2.69 m, 2.88 m
Width 8', 8' 9"
2.67 m
Width over tracks  
Ground clearance 16"
Ground contact length 148"
Ground pressure 11.5 psi
Turret ring diameter  
Armament  
Main 155 mm M1917
OR 155 mm M1917A1
OR 155 mm M1918
OR 155 mm M1918M1
Secondary  
MG 1: 0.5" Browning MG
1: 12.7 mm Browning MG
MG - anti aircraft  
Side arms  
Quantity  
Main 6, 10
Secondary  
MG  
Side arms  
Armor Thickness (mm) 50
Front: 1"
Side: 0.4"
Hull Front, Upper  
Hull Front, Lower  
Hull Sides, Upper  
Hull Sides, Lower  
Hull Rear  
Hull Top  
Hull Bottom  
Turret Front  
Turret Sides  
Turret Rear  
Turret Top  
Engine (Make / Model) Continental R-975
Wright
Bore / stroke  
Cooling Air
Cylinders R-9
Radial
Capacity  
Net HP 353, 400@2,400 rpm
Power to weight ratio  
Compression ratio  
Transmission (Type) Synchromesh
5 forward, 1 reverse
Steering Controlled differential
Steering ratio  
Starter Electric
Electrical system 24-volt
Ignition Magneto
Fuel (Type) Gasoline, Gasoline
Octane  
Quantity 200 gallons
Road consumption 0.6 mpg
Cross country consumption  
Performance  
Traverse 14° left, 14° right
Speed - Road 21 mph, 24 mph
38 kph, 39 kph
Speed - Cross Country 5-21 mph, 12 mph
Range - Road 120 miles, 140 miles
225 km
Range - Cross Country  
Turning radius  
Elevation limits -5° to +30°
Fording depth 3'
Trench crossing 6', 7' 6"
Vertical obstacle 18", 2'
Climbing ability 22° (40%) slope
Suspension (Type) Vertical volute
Wheels each side 3 x 2-wheeled bogies
Return rollers each side 3
Tracks (Type) Rubber block, double pin
Length  
Width 16", 16.5"
Diameter  
Number of links 79
Pitch 6"
Tire tread  
Track centers/tread 6' 11", 6.95'
  M30 Cargo Carrier
Crew  
Physical Characteristics  
Weight 47,000 lb
Length 19' 10"
Height 10'
Width  
Width over tracks  
Ground clearance  
Ground contact length  
Ground pressure  
Turret ring diameter  
Armament  
Main  
Secondary  
MG  
MG - anti aircraft .50 cal Browning
Side arms  
Quantity  
Main 40
Secondary  
MG 1,000
Side arms  
Armor Thickness (mm)  
Hull Front, Upper  
Hull Front, Lower  
Hull Sides, Upper  
Hull Sides, Lower  
Hull Rear  
Hull Top  
Hull Bottom  
Turret Front  
Turret Sides  
Turret Rear  
Turret Top  
Engine (Make / Model) Continental R-975
Bore / stroke  
Cooling  
Cylinders  
Capacity  
Net HP  
Power to weight ratio  
Compression ratio  
Transmission (Type)  
Steering  
Steering ratio  
Starter  
Electrical system  
Ignition  
Fuel (Type)  
Octane  
Quantity  
Road consumption  
Cross country consumption  
Performance  
Traverse  
Speed - Road 24 mph
Speed - Cross Country 12 mph
Range - Road 140 miles
Range - Cross Country  
Turning radius  
Elevation limits  
Fording depth 3'
Trench crossing 7' 6"
Vertical obstacle 2'
Climbing ability  
Suspension (Type) Vertical volute.
Wheels each side  
Return rollers each side  
Tracks (Type)  
Length  
Width 16.5"
Diameter  
Number of links  
Pitch  
Tire tread  
Track centers/tread 6' 11"

Sources:

  1. The Encyclopedia of Tanks and Armored Fighting Vehicles - The Comprehensive Guide to Over 900 Armored Fighting Vehicles From 1915 to the Present Day, General Editor: Christopher F. Foss, 2002
  2. British and American Tanks of World War Two, The Complete Illustrated History of British, American, and Commonwealth Tanks 1933-1945, Peter Chamberlain and Chris Ellis, 1969
  3. -
  4. Tank Data, Aberdeen Proving Grounds Series, 1968?
  5. Profile: AFV Weapons 26: Hellcat, Long Tom and Priest and Complete Check List of all U.S. World War II Self-Propelled Weapons, Colonel Robert J. Icks, 1971
  6. World Encyclopedia of Armored Fighting Vehicles, Jack Livesey, 2006
20th Century American Military History Crucial Site