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United States' M18 Gun Motor Carriage⁶, Hellcat⁶

M18 US Ordnance Dept⁶	M18 US Ordnance Dept⁶	M18 supporting 2nd Battalion, 397th Infantry Regiment in Wiesloch, Germany on 1 April 1945⁶ US Army⁶	M18 Aberdeen Tank Museum
M18	M18	M18	M18

Design

In February 1944, it was standardized as the M18 Gun Motor Carriage and nicknamed the Hellcat.^1,6,7

The M18 Hellcat had three compartments: driver's, fighting, and engine.⁶

Driver's Compartment

The driver sat on the left and the assistant driver on the right.⁶ Located between them was the transmission with the shift levers on top.⁶ This allowed for either to shift the gears.⁶ Each had an accelerator pedal with the assistant driver having a lockout mechanism.⁶ Each had steering levers that would hang down, and the levers could be moved out of the way.⁶ On the left side of the driver was the instrument panel.⁶ There were adjustable seats for both.⁶ In the roof each had hinged double doors.⁶ These also had periscopes.⁶

Fighting Compartment

The turret basket contained three folding and adjustable seats.⁶ The commander was on the left side behind the gunner.⁶ The loader was located on the right side of the 76 mm gun.⁶

The gunner could use either a hydraulic or hand traverse control to rotate the turret.⁶ He also had an azimuth control.⁶ Periscopic and telescopic sights were used by the gunner.⁶

There was an auxiliary generator, located in the sub floor at the right front of the turret, that was used to recharge the batteries.⁶

The assistant driver had a portable fire extinguisher beside him.⁶

The turret bulge held the radio equipment.⁶

Engine Compartment

The fuel tanks were located on each side of the engine.⁶ The left held 75 gallons and the right 90 gallons.⁶

A propeller shaft went under the sub floor transmitted power from the engine to the transmission.⁶

The torqmatic transmission was mounted on extension rails so it could be slid out for repairs.⁶

There were controls inside and outside of the engine compartment that controlled its fire extinguisher.⁶

Starting with vehicle 1,700 it had blowers that would move hot air over the oil cooler, the battery, the engine, and to the crew.⁶ This equipment was sometimes installed at tank depots for earlier vehicles to winterize them.⁶

Main Armament

The M18 was armed with the 76 mm M1A1, M1A1C or M1A2 L/55 gun.⁶

The M1A1 had no muzzle brake.⁶ The M1A1C has threads for a muzzle brake and the barrel had rifling of one turn for each 40 calibers.⁶ M1A2 had threads for a muzzle brake and rifling of one turn for each 32 calibers.⁶

A travel lock was located in the turret for vehicles 1 - 1,857.⁶ This was a swinging lever with a pin.⁶ From vehicle 1,858 there was a spring loaded ball stud.⁶

Could penetrate 101 mm. Muzzle velocity 2,600 ft/sec.⁵ The AP shell weighed 15.4 lbs.⁵ It could fire a HE shell 14,000 yards.⁵

Prototype

On December 2, 1941, a memorandum from the G-3 to the G-4 of the General Staff recommended that a gun motor carriage be developed to carry a 37 mm M6 gun on a Christie type suspension.⁶ On April 1, 1942, the Ordnance Department suggested that a 57 mm M1 gun be used.⁶

On April 18, 1942, it was agreed to construct two prototypes that would be identified as the T49 Gun Motor Carriage.⁶ It was to be mobile, weigh around 12 tons, have a crew of five, reach a speed of 50 mph, armor was to be 7/8" on the turret, and 3/8" all around on the hull.⁶

The first prototype was tested and as a result the Tank Destroyer Command and the Ordnance Department wanted the second prototype to have a 75 mm M3 gun.⁶ This became the T67 Gun Motor Carriage.⁶ It was to have its armor increased to 1" in front.⁶ The side armor was reduced and the top and bottom was increased.⁶

The prototypes had helical coil suspensions.⁶ Two Buick 320 cubic inch gasoline engines produced a total of 330 HP.⁶

In late 1942, after the testing of a prototype at the Aberdeen Proving Ground, the Special Armored Vehicle Board recommended that the T67 have a standard engine, a 76 mm gun, and a torsion bar suspension.⁶ The Secretary of War approved the building of six prototypes.⁶ These would carry the 76 mm M1 in an open turret without a basket.⁶ The Continental R975-C1 engine was used.⁶ These prototypes were designated the T70 Gun Motor Carriage.⁶

Production

On January 7, 1943, without testing the T70 Gun Motor Carriage prototypes, the Army Service Forces ordered 1,000 to be constructed.⁶ The first first T70 was delivered in July 1943.⁶

M18: 2,507^3,6,7
- Manufacturer: Buick Motor Division (GMC)⁵
- Production: July 1943 - October 1944⁷
T41, T41E1 (M39): 640⁶
T86: 3 prototypes⁶
- Manufacturer: Marmon-Herrington⁶

M18 Monthly Production
July 1943	6⁶
August 1943	83⁶
September 1943	112⁶
October 1943	150⁶
November 1943	267⁶
December 1943	194⁶
January 1944	250⁶
February 1944	218⁶
March 1944	170⁶
April 1944	150⁶
May 1944	150⁶
June 1944	150⁶
July 1944	150⁶
August 1944	150⁶
September 1944	150⁶
October 1944	157⁶

T41 Monthly Production
October 1944	10⁶
November 1944	60⁶
December 1944	163⁶
January 1945	180⁶
February 1945	180⁶
March 1945	107⁶

Variants

M44 Armored Personnel Carrier: The top hatches were side hinged.⁶
M44E1 Armored Personnel Carrier (T17 Command Post Vehicle): Hull raised 10".⁶ Hatches front hinged.⁶ Used during Korean War by the United States Air Force and called the Tactical Air Control Party (TACP) vehicle.⁶
T9 Armored Utility Vehicle: Parts from M18 and M22.⁶ Had one less bogie wheel and only two support rollers.⁶ 9.5 tons in weight.⁶
T41 Armored Utility Vehicle:

The T41 was used as a prime mover for the 3" gun.⁶
Had a ring for a .50 cal Browning MG installed in the front. Weighed 35,000 lb. Crew 2 plus 7 passengers. Height 5' 11".
T41E1 (M39): Reconnaissance, troop carrier.⁶ Became the M39 in early 1945.⁶
T49 Gun Motor Carriage: Prototype with 37 mm M6 gun.⁶

US Ordnance Dept⁶
T65 Flame Tank: Converted M39.⁶ Carried Canadian Iroquois flame thrower.⁶

US Ordnance Dept
T67 Gun Motor Carriage: Prototype with 75 mm M3 gun.⁶

US Ordnance Dept⁶
T70 Gun Motor Carriage: Prototype with 76 mm M1 gun.⁶ Used Torsion bar suspension.⁶

US Ordnance Dept⁶

Buick Motor Division, General Motors Corporation⁶

US Ordnance Dept⁶
T86 Amphibious Gun Motor Carriage (Esch Device): Removed the hull plate down to the sponson line and put in a lighter amphibious hull.⁶ The reduction gear was lowered.⁶ Was to use the 21" track from M24, however the tracks weren't ready so the M18's 14" track was used.⁶ Propelled in water by its tracks.⁶ Had speed of 4.6 mph in water.⁶
T86E1 Amphibious Gun Motor Carriage: Had two 26" screws to propel it in water.⁶ These were located in tunnels with two rudders, controlled by cables, behind them.⁶ Testing started in April 1944.⁶ Weighed 23 tons.⁶ Had speed of 6.2 mph in water.⁶ Later testing removed one screw.⁶
T87 Amphibious Gun Motor Carriage: Same as T86E1 but with 105 mm howitzer.⁶ Was 2' 3" shorter than T86E1.⁶
T88 105 mm Howitzer Motor Carriage: In August 1944, the Ordnance Department wanted to develop a vehicle with the 105 mm T12 howitzer. By December 1944, a pilot model was finished. It was identical to the M18 except for the gun and the sights. It was canceled in August 1945.

Usage

Used by tank destroyer battalions in Europe.¹

It first saw action in the Summer of 1944 in Europe.¹ One unit to use it quite effectively was the 630th Tank Destroyer Battalion in July 1944 reported destroying 53 Panthers & Tigers and 15 self propelled guns with only a loss of 17 of their M18s.¹

Post World War II

After World War II the M18 was used by Argentina, Austria, Nationalist China, West Germany, Greece, Iran, Soviet Union, Turkey, Venezuela, and Yugoslavia.⁶

The M39 was supplied to the Netherlands and West Germany.⁶

	T49 Gun Motor Carriage⁶	T67 Gun Motor Carriage⁶	M18 Gun Motor Carriage⁶
Crew			Commander, driver, gun crew (3)² Commander, loader, gunner, driver, assistant driver⁶ 5^1,2,3,5,7
Physical Characteristics
Weight	16 tons⁶	16 tons⁶	37,557 lb^3,6, 40,000 lb^2,7 17.9 tons¹, 19.5 tons⁵ 17,036 kg³, 18,142 kg¹, 18,160 kg⁷
Weight - empty			35,526 lb⁶
Length w/gun	17' 10.5"⁶	17' 10.5"⁶	21' 10"^1,2,3,6,7 6.65 m³, 6.655 m⁷, 6.7 m¹
Length w/o gun			17' 4"², 17.5'⁵, 17' 10"^3,7, 21' 2"⁶ 5.436 m⁷, 5.44 m³
Height	7' 0.25"⁶	7' 0.25"⁶	8.4' (top of AA)⁵, 8' 5"^1,2, 8' 5 7/16"⁶, 8' 5.44"⁷, 8' 5.5"³ 2.5765 m⁷, 2.58 m³, 2.6 m¹
Width	8' 9.75"⁶	8' 9.75"⁶	9.1'⁵, 9' 5"^3,6, 9' 9"^1,2,7 2.87 m³, 2.97 m¹, 2.972 m⁷
Width over tracks
Ground clearance			14", 14.25"^5,6
Ground contact length			9' 8", 116.5"⁵
Ground pressure			11.9 psi⁶ 12.5 psi⁵
Turret ring diameter
Armament
Main			76 mm⁷ 76 mm M1A1² 76.2 mm (3") M1A1³ 3" (76 mm) M1¹ 76 mm M1A1, L/53⁵ 76 mm M1A1 L/55⁶
OR			76 mm M1A1C² 76 mm M1A1C L/55⁶
OR			76 mm M1A2² 76 mm M1A2 L/55⁶ 76.2 mm (3") M1A2³
Secondary
MG			12.7 mm (.50 cal) MG^1,3,7
MG - bow	1: MG⁶
MG - antiaircraft			.50 cal Browning MG² .50 cal M2 Browning M1919A4⁶ .50 cal M2 MG⁵
Side arms			M3 .50 cal Tripod mount 5: M1 Carbines Grenades Smoke Pots
Quantity
Main			45^1,2,3,5,6,7 (HE, APC, HVAP, Canister, Smoke)
Secondary
MG			800^2,7, 840⁶, 1,000⁵
Side arms			450 12 4
Armor Thickness (mm)			7², 12² Front: 0.5"⁵ Side: 0.5"⁵
Hull Front, Upper			0.5"^6,7 12.7⁷
Hull Front, Lower			12
Hull Sides, Upper			0.5"^6,7 12.7⁷
Hull Sides, Lower			12
Hull Rear			0.5"^6,7 12.7⁷
Hull Top			5/16"⁶ 8
Hull Bottom			0.25"⁶ 7
Turret Front			0.75"⁵, 1"^6,7 25.4⁷ Mantlet: 0.5"⁵
Turret Sides			0.5"^5,6 12
Turret Rear			0.5"⁶ 12
Turret Top
Engine (Make / Model)	2: Buick⁶	2: Buick⁶	Continental R-975 C1^1,3 Continental R-975² Continental R975C4⁵
Vehicle 1 - 1,349			Continental R975-C1⁶
Vehicle 1,350 - 2,507			Continental R974-C4⁶
Bore / stroke			4 cycles⁵
Cooling			Air^5,6
Cylinders			R-9⁵, 9⁶
Capacity
Net HP			340³, 400⁷, 400@2,400 rpm⁵ C1: 340⁶ C4: 400⁶
Power to weight ratio
Compression ratio
Transmission (Type)			Torqmatic^5,6 3 forward 1 reverse^5,6
Steering			Controlled differential⁵
Steering ratio
Starter			Electric⁵
Electrical system			24-volt⁵
Ignition			Magneto⁵
Fuel (Type)			Gasoline^3,5
Octane
Quantity			165 gallons⁶, 169 gallons⁵, 170 gallons⁶
Road consumption			0.6 mpg⁵
Cross country consumption
Performance
Traverse			360°^2,5, electric Hydraulic⁵
Max speed	51 mph⁶	51 mph⁶	45 mph⁵, 45-50 mph², 50 mph¹, 55 mph^3,6,7 80 kph¹, 88.5 kph^3,7
Cross country speed			20 mph²
Road radius			105 miles^3,5,6, 150 miles^1,2,7 169 km³, 240 km¹, 241 km⁷
Cross country radius			150 miles⁵
Turning radius			33'⁶
Elevation limits			-10° to +19.5 °² , -10° to +20°^5,6
Fording depth			4'^2,3,5,6 1.22 m³
Trench crossing			6' 2"^2,3,6, 6.2'⁵ 1.88 m³
Vertical obstacle			3'^2,3,5,6 0.91 m³
Climbing ability			31° (60%) slope⁵ 60%⁶
Suspension (Type)	Helical spring⁶	Helical spring⁶	Torsion bar^2,5,6
Wheels each side	5⁶	5⁶	5^5,6
Return rollers each side	2⁶	2⁶	4^5,6
Tracks (Type)			T69, dry pin, steel shoe⁵ T69 steel⁶
Length
Width	12"⁶	12"⁶	1'⁵, 1' 2.38"⁶, 1' 2.4"^2,5,7 0.3657 m⁷
Diameter			26"⁶
Number of links			83^5,6
Pitch	5 3/32"⁶	5 3/32"⁶	5 3/32"⁶, 5.25"⁵
Tire tread
Track centers/tread			7.9'⁵, 10' 10.25"^2,7 3.308 m⁷

Sources:

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
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
The Encyclopedia of Weapons of World War II, Chris Bishop, 1998
-
Tank Data, Aberdeen Proving Grounds Series, 1968?
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
Airfix Magazine Guide #26 American Tanks of World War 2, Terry Gander and Peter Chamberlain, 1977