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United States' M12 Gun Motor Carriage
Nickname: door knocker⁶

M12	M12 At Battle of Bulge	M12 In Germany 1945.	M12
M12 Aberdeen Tank Museum	M12

Design

The Chief of Ordnance ordered a pilot model to have a 155 mm M1918M1 gun put onto a M3 medium chassis.^1,5 This was designated the T6 and work began on it in June 1941.^1,5

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 M12.⁶

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.⁶ After World War I they were placed into storage.⁶

The 155 mm gun fired a 95 lb shell at a muzzle velocity of 2,380'/sec and a range of 18,000 yards.⁴

Firing Spade

The M12 had a spade at the rear to help stabilize against the recoil of the gun.¹ 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.¹

The T6 prototype started testing at the Aberdeen Proving Ground in February 1942.^1,5 It had some modification done and was sent to Fort Bragg for the Field Artillery Board to test.⁵ The T6 proved acceptable, except to the Army Ground Forces, who felt towed artillery was good enough.^1,6

During tests the T6 was fired, moved six miles, and then fired again.⁵ This took a total of 35 minutes to complete.⁵ A tractor towed 155 mm gun required three hours to do the same thing.⁵ The Ordnance Board ordered 50 initially, which was increased to 100.^1,5

Production

Initial production of 100 of the M12 and M30 were completed in March 1943 by Pressed Steel Car Company.⁵ These were stored or used for training.⁵

When the Normandy landings was getting closer it was decided to remanufacture them.⁵ Baldwin Locomotive Works rebuilt 74 of them by May 1944 with the M4 chassis.^1,5

• M12 Gun Motor Carriage:
  • Manufactured by: Pressed Steel Car Company^4,5
• M30 Cargo Carrier:
  • Manufactured by: Pressed Steel Car Company⁵
• Total: 100⁵
  • Production: late 1943 - March 1944⁶

Variants

• M12 Gun Motor Carriage:
• M30 Cargo Carrier: Identical to M12 except no gun.⁶ There was on M30 for each M12.⁶ The crew primarily traveled in the M30.⁶ 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.⁶

Usage

Eventually 74 were sent to Europe in June 1944.^5,6 They were used in the taking of Cologne⁵ and in busting the bunkers in the Siegfried Line¹.

Used in Italy, France, and Germany.⁴

		M12 Gun Motor Carriage	M30 Cargo Carrier
Crew		Commander, driver, gun crew (4)2,5 54, 61,2,5,6
Physical Characteristics
Weight		58,000 lb2,5 26.3 tons1, 27.1 tons4, 29 tons6 26,762 kg1, 29,464 kg6	47,000 lb2,5
Length w/gun	22' 1"	22.1'4, 22' 1"5,6, 22' 3"1,2 6.67 m1, 6.73 m6	19' 10"2,5
Length w/o gun
Height	8' 10"	8.8'4, 8' 10"2,5,6, 9' 6"1 2.69 m6, 2.88 m1	10'2,5
Width	8' 9"	8'4, 8' 9"1,2,5,6 2.67 m1,6
Width over tracks
Ground clearance	17 1/8"	16"4
Ground contact length	14' 3"	148"4
Ground pressure	11.6 psi	11.5 psi4
Turret ring diameter
Armament
Main	155 mm M1917	155 mm M19171
OR	155 mm M1918A1	155 mm M1917A14
OR	155 mm M1918M1	155 mm M19181
OR		155 mm M1918M12,5,6
Secondary
MG		1: 0.5" Browning MG6 1: 12.7 mm Browning MG6
MG - anti aircraft			.50 cal Browning2,5
Side arms	5: .30 cal Carbines Grenades
Quantity
Main		64, 101,2,5,6	402,5,6
Secondary
MG	1,000		1,0002,5
Side arms	22
Armor Thickness (mm)	(Actual thickness at horizontal)	506 Front: 1"4 Side: 0.4"4
Hull Front, Upper	1.5-2" (3.5")
Hull Front, Lower
Hull Sides, Upper	1"
Hull Sides, Lower
Hull Rear	0.75"
Hull Top	0.5"
Hull Bottom	0.5-1"
Turret Front	Shield: 0.75"
Turret Sides
Turret Rear
Turret Top
Engine (Make / Model)	Continental R-975 C1	Continental R-9752,5,6 Wright4	Continental R-9752
Bore / stroke
Cooling		Air4
Cylinders		R-94 Radial6
Capacity
Net HP		3535,6, 400@2,400 rpm4
Power to weight ratio
Compression ratio
Transmission (Type)	Syncromesh	Synchromesh4 5 forward, 1 reverse4
Steering		Controlled differential4
Steering ratio
Starter		Electric4
Electrical system		24-volt4
Ignition		Magneto4
Fuel (Type)		Gasoline4,5, Petrol6
Octane
Quantity		200 gallons4
Road consumption		0.6 mpg4
Cross country consumption
Performance
Traverse		14° left, 14° right2,5
Max speed	24 mph	21 mph4, 24 mph1,2,5,6 38 kph1, 39 kph6	24 mph2
Cross country speed	12 mph	5-21 mph4, 12 mph2,5	12 mph2
Road radius	140 miles	120 miles4, 140 miles1,2,5,6 225 km6	140 miles2
Cross country radius
Turning radius	35'
Elevation limits		-5° to +30°2,5
Fording depth	3'	3'2,4,5	3'2
Trench crossing	7' 6"	6'4, 7' 6"2,5	7' 6"2
Vertical obstacle	2'	18"4, 2'2,5	2'2
Climbing ability		22° (40%) slope4
Suspension (Type)	Vertical volute	Vertical volute2,4,5	Vertical volute.2
Wheels each side		3 x 2-wheeled bogies4
Return rollers each side		34
Tracks (Type)		Rubber block, double pin4
Length
Width	16.5"	16"4, 16.5"2,5	16.5"2
Diameter
Number of links		794
Pitch		6"4
Tire tread
Track centers/tread	6' 11"	6' 11"2,5, 6.95'4	6' 11"2

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

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