105 mm Howitzer Motor Carriage M37

United States of America (1945-Late 1950s)
Howitzer Motor Carriage – 316 Built

The 105 mm Howitzer Motor Carriage M37 (HMC) represented a step forward in artillery technology, envisioned as the successor to the widely utilized M7 Priest sporting a similar 105 mm howitzer gun, but on the more modern M24 Chaffee chassis. Despite being adopted, the end of the Second World War curtailed the M37’s widespread utilization. While initially slated to replace its predecessors, boasting mobility and modernized features, the M37’s deployment remained limited, never fully replacing the previous self-propelled guns and getting quickly taken out of service itself due to a change in doctrine due to the need to seal vehicles for nuclear war.

The Beginning

The M37 HMC was designed to fill the need for a lightweight and high-speed mobile artillery platform to replace the M7 HMC. The M7 HMC Priest, which started production in April 1942, was vulnerable when used in close support because it had no direct fire sight, inadequate ammunition protection, and thin frontal armor. However, despite this, it continued to serve into the Korean War. This led to the development of other howitzer-armed vehicles, including the M4 105 mm, M4A3 105 mm, M8 Scott, and M37 HMCs.

Between January and February 1943, various studies were performed on the T16 4.5 inch (11.4 cm) GMC (Gun Motor Carriage), based on a lengthened M5 light tank chassis, by the Field Artillery Board and Aberdeen Proving Ground. It was found that it was less expensive, weighed less, and was more mobile than the M7 HMC. However, the howitzer mounted on the rear of the vehicle caused the gun to need to be “excessively high” to allow for the desired 10° of depression and would cause the T16 to be back heavy. This meant that it would not be adopted. Additional studies showed that exchanging the gun for a 105 mm howitzer mounted in the rear would, while maintaining “good all round armor”, give the desired traverse range while allowing it to be used in direct and indirect fire roles.

Work Starts

During July 1943, work on the procurement of a pilot vehicle for a 105 mm Howitzer Motor Carriage based on the T24 light tank, the pilot vehicle for the M24, started, designated T76 105mm Howitzer Motor Carriage (T76 105 mm HMC). The T24 was likely chosen as it was bigger than the earlier M3 and M5 Stuart light tanks.

The M24 Chaffee (designated Light Tank, M24) was initially designed in 1943, with the pilot being delivered on 15 October 1943, and entered service in 1944. The M24 was created to replace the earlier obsolete M3 and M5 Stuart light tanks. These did not have sufficient armament to effectively combat most tanks, and, as such, the M24 was armed with a 75 mm M6 gun and an M2HB 12.7 mm (0.5 in) machine gun which was a vast improvement over the M3 and M5’s 37 mm gun.

On 10 June 1943, the Ordnance Council, in OCM 20679, recommended a pilot vehicle, designated 105 mm howitzer motor carriage T76, be developed and procured. A wooden mock-up of the T76 was created and subsequently reviewed by the Artillery Officers from the Ordnance Board. They advised that the vehicle was to be used as mobile artillery to support the proposed light tank units and subsequently needed a high rate of fire.

To allow for the desired rate of fire, the crew was increased from six to seven, and the size of the fighting compartment was increased. This allowed the crew to work efficiently without unnecessary interference while staying within the armor. The size of the fighting compartment was increased by relocating the engine to the rear instead of the middle. This added 30.5 cm (12 in) to the fighting compartment. A total of 12.7 mm (0.5 in) of armor was used throughout the design. The assistant driver was removed, likely so that the gun mount could be moved to be centrally located and moved forward, lengthening and increasing the fighting compartment by 15.3 cm (6 in). This also allowed the anti-aircraft ring mount to be placed to the driver’s right, where the co-driver’s hatch was previously located.

Due to an inspection by the Ordnance Board, a new mock-up was created in September 1943, and a gun crew from the Armored Command assessed various stowage arrangements using different heights and amounts of equipment. After the best arrangement had been found, later in September, the updated mock-up was reviewed by representatives from the Army Ground Forces, the Armored Board, and the Tank-Automotive Center. The representatives approved of the mock-up’s arrangement and requested at least two pilot models with the same characteristics so that they could be tested. During December 1943, the Army Services Force decided to approve the characteristics to be implemented on the T76 105 mm HMC.

To speed up the delivery of the pilot vehicles, the Tank-Automotive Center designed and procured the gun mount. This work was finished, and the Gun Mount T14 was proof fired on 17 March 1944, at which point malfunctions were recorded, modifications subsequently applied, and the design of the necessary additional or replacement parts was started. The resultant changes were implemented, and the new mount had reinforcements welded on to attach the mount to the vehicle. This caused the maximum elevation to decrease from 45° to 42°. The Armored Board approved this and was still present in production vehicles. The elevating mechanism was redesigned to allow for an improved support pad and increased elevation radius. In addition, modified sleeves or throttling groves were created and placed into the recoil cylinders.

This new mount was tested at the Rock Island Ordnance Center (Illinois) sometime between 4 and 11 June 1944 and was found to be very satisfactory. After this, the vehicle was sent to Aberdeen Proving Ground (Maryland) to perform extended firing tests, which also checked the fire control equipment. These tests found the design to be satisfactory, provided the following issues were rectified:

1. When operating with all hatches closed and canvas cover in place, the temperature was too high for the crew to operate.
2. The gun’s recoil guard was too short, endangering the crew.
3. The breech block opened due to the operating handle unlatching, which made it hard for the loader to remove the shell casing.
4. When traversing right, the interphone communication control box would block the traverse wheel, limiting the traverse.
5. The inner gun shield would bend, which rubbed against the opening, preventing the gun from easily elevating and depressing.
6. The Panoramic Sight Mount T96 loosened and had excess dispersion when firing.
7. The travel lock was unsatisfactory.

After the tests at Aberdeen Proving Ground, Pilot No1 was sent to Armored Command at Fort Knox (Kentucky) for automotive tests, including stowage requirements. The design was well-liked and was found to be superior to the M7 HMC. Some of the superior factors included fuel economy, climbing slopes, and armor protection. After these tests, Pilot No1 was returned to Rock Island Ordnance Center to fit a modified gun mount, fire control, gun travel lock, and other minor modifications.

After Pilot No1 was returned to Rock Island Ordnance Center, Pilot No2 was sent as well to receive the same modifications. After this, it underwent firing tests at Aberdeen Proving Ground. It was then sent to the American Car and Foundry Company to be reworked, including replacing the M49C machine gun ring mount for the T107 anti-aircraft ring mount, the elimination of the SCR 510 (to provide space for more 105 mm ammunition), redesigning the rear hull door to act as a loading ramp, and the ammunition stowage being changed by stowing the rounds horizontally increasing from 68 to 128 rounds. After this, it served as a model for production drawings. After these changes, the T76 was standardized as the 105 mm Howitzer Motor Carriage M37.

Production

A production order for 750 vehicles was issued on 12 December 1944, to be completed before 31 December 1945. This was later reduced to only 448, likely due to the end of the war. With the sighting and fire control equipment standardized during July 1944, production started in January 1945 and lasted until 1953. Around 316 M37s were actually produced out of the 448 ordered, with around 150 produced post-war by American Car & Foundry and the remainder produced by Cadillac and Massey-Harris, likely starting during World War 2. However, some sources, in particular R. P. Hunnicutt, state that only 150 were built, but this could be a confusion with which manufacturers created the vehicles. However, no serial numbers above 150 could be found during research.

Design

Dimensions

The M37 was 5.49 m (6 yd) long, 3 m (3.28 yd) wide, and 2.84 m (3.11 yd) tall.

Armor

The armor was made of 9.53 mm to 12.7 mm of rolled homogeneous steel, which was welded together.

Plate	Thickness		Angle
	(mm)	(inches)	(all angles are from the vertical)
front top	12.7 mm	0.5 in	90°
front floor	12.7 mm	0.5 in	90°
upper front	12.7 mm	0.5 in	60°
lower front	12.7 mm	0.5 in	45°
lower rear	12.7 mm	0.5 in	45°
front sides	12.7 mm	0.5 in	12°
fighting compartment	12.7 mm	0.5 in	0°
upper rear	12.7 mm	0.5 in	0°
howitzer shield	12.7 mm	0.5 in	0° to 38°
rear floor	9.53 mm	0.375 in	90°

Armament

The M37 was armed with an M4 105 mm Howitzer, descended from the towed M2A1 Howitzer. The M4 Howitzer was initially designed to fit in the M4 Sherman’s turret in an M5 mount in the front of the hull. Compared to the M2A1, the M4 has a modified breech and a cylindrical recoil surface.

The M4 Howitzer had a fire rate of eight rounds per minute. In the M37 HMC, the M4 Howitzer could manually traverse 51.7°, 25.4° to the left and 26.3° to the right. Elevation was from -10.5° to +42.8°. The howitzer had very little overhang forward and a fire height of 1.7 m (1.83 yd).

The main gun used one of each of the following:

1. T92 Periscopic Sight, which made direct fire easier
2. M12A2 Panoramic telescope (with an M19 light instrument), normally used to lay the weapon on the azimuth for indirect fire
3. M76G Telescope (on T96 Telecop mount, with an M33 light instrument)
4. M1 Gunner Quadrant, used to lay elevation and measuring angles of elevation
5. T14 Range Quadrant (with an M18 light instrument)
6. M1 Aiming Post
7. M14 Light Aiming Post
8. M22 Fuse Setter

The gun could fire a variety of shells, including: the M1 HE (High-Explosive), M67 HEAT (High-Explosive Anti-Tank), M84 smoke (white or colored), M60 white phosphorus or mustard gas, M1 empty shell, and the M14 Drill cartridge. On board, there were 126 rounds, of which 6 were ready to fire.

M4 Howitzer Rounds fired from the M37 HMC
Type	Model	Weight of the round	Length of the round	Warhead Contents	Muzzle velocity	Range (at 44º)
HE	M1 HE Shell	19.08 kg (42.07 lb)	78.87 cm (31.05 in)	TNT or an equal mix of TNT and amatol	472 m/s (1,550 ft/s)	11,160 m (12,205 yd)
HEAT	M67 HEAT
Smoke, white	M84 HC BE Shell	19.02 kg (41.94 lb)	80 cm (30.49 in)	HC (Zinc chloride) smoke mixture	472 m/s (1,550 ft/s)	11,160 m 12,205 yd
Smoke, colored	M84 BE Shell	Green, Violet: 17.95 kg 39.57 lb Red 18.04 kg 39.77 lb Yellow 17.86 kg 39.37 lb		Various Smoke mixtures 44.38 lb	Likely greater than 472 m/s (1,550 ft/s)	Likely greater than 11,160 m (12,205 yd)
Smoke	M60 WP Shell	19.83 kg (43.71 lb)	78.94 cm (31.08 in)	White phosphorus	472 m/s (1,550 ft/s)	11,160 m (12,150 yd)
Smoke	M60 FS Shell	19.2 kg (42.32 lb)	Likely around 78.94 cm (31.08 in)	White phosphorus	Likely around 472 m/s (1,550 ft/s)	11,160 m (12,150 yd)
Chemical	M60 H Shell	Likely around 19.2 kg (42.32 lb)	Likely around 78.94 cm (31.08 in)	Mustard gas	Likely around 472 m/s (1,550 ft/s)	11,160 m (12,150 yd)
Practice	M1 Empty Shell	2.83 kg (6.23 lb)	15.24 cm (6 in)	No warhead it had a 0.68 kg (1.5 lb) or 2 lb (0.91 kg) charge the rest was filled with sand	N/A	N/A
Drill	M14 Drill Cartridge	18.76 kg (41.35 lbs)	78.92 (31.07 in)		N/A	N/A
Blank		2.83 kg (6.23 lbs)		M15 Cartridge Case wth No warhead it had a 2 lb (0.91 kg) charge	N/A	N/A

The vehicle had a 12.7 mm (0.50 in) Browning M2HB machine gun, which was primarily for anti-aircraft use. This was mounted on the front left of an M68 Concentric Ring Mount, which allowed the gun to manually traverse 360°. There were 990 stowed rounds, likely stowed in the sponsons.

The vehicle initially carried one 0.45 caliber submachine gun, likely an M3 or M3A1 “Grease Gun”, with 750 rounds and four 0.30 caliber carbines, likely the M1 model. However, this was likely changed to either all M3 submachine guns or four M3 submachine guns and one M1 0.30 carbine later in the vehicle’s life.

Automotive and Performance

The vehicle used a liquid-cooled two 8-cylinder Cadillac Series 44T24 engines, with a net horsepower of 220 hp@3,400rpm and a gross horsepower of 296 hp@3,200rpm. The engine developed a net torque of 480 ft-lb@1,200rpm and a gross torque of 560 ft-lb@1,200rpm. The electrical system ran at 24 volts at 3,000 watts with a 50 amp panel set. The vehicle had an unloaded weight of 17.2 tonnes (19 tons) and a combat weight of 25 tonnes (23.1 tons). The engine held 9.09 liters (8 quarts) of engine oil and 45.5 liters (40 quarts) of coolant for the entire system.

The M37 had a fuel capacity of 416.4 liters (110 gallons) of 80-octane gasoline in two tanks, each holding half the fuel. These were located on either side of the engine compartment.
Steering was through a controlled differential with steering levers, the brakes were mechanical external contracting, and the transmission was a herringbone gear, twin hydramatic, with 8 speeds forward and 4 in reverse. Each engine and transmission assembly weighed 529 kg (1,166 lbs).

The top speed on road was 56 km/h (35 mph), with a cruising range of around 161 km (100 mi) on road and a turning circle of 12.2 m (40 ft). The maximum length of trench it could cross was 2.44 m (8 ft). It had a climbing grade ascending ability of 60° and could cross a step of 1 m (3.3 ft). It had a bridging weight of 17.7 tonnes (19.5 tons), and a fording depth of 2.13 m (7 ft) when waterproofed. The fire protection system consisted of a 4.54 kg (10 lb) C02 fixed fire extinguisher and a 1.81 kg (4 lb) one.

Suspension

The suspension consisted of torsion bars with five individually sprung dual road wheels, with the first two and last two road wheels with shock absorbers. The tyre size on the road wheels was 57.2 cm (22.5 in) by 11.4 cm (4.5 in). The drive sprockets had 13 teeth, the idlers were at the rear, and four return rollers held the upper part of the track. The size of the idler was 57.2 cm (22.5 in) by 12.7 cm (5 in). The tread was 2.4 m (2.67 yd), and the ground clearance was 46 cm (0.5 yd). The ground pressure with the T72 tracks was 0.814 kg/cm² (11.6psi). The track used 80 track links with a ground contact length of 3.15 m (124 in), with a pitch of 78.7 mm (5.5 in).

There were two main types of tracks, T72 and T85E1. The T72 were steel and rubber bushed with a single pin that used parallel grousers. The T85E1 used a rubber chevron contact pad, the rest being steel, with a double pin with a center guide. When using the T72 track, the track width was 40.6 cm (16 in). When using the T85E1 track, the track width was 35.6 cm (14 in) without extended-end connectors and 41.9 cm (16.5 in) with extended-end connectors.

Crew

In April 1945, the M37 HMC had a crew of 7: a chief of section in the left of the hull, a gunner in the left rear of the hull, four cannoneers (the artillery term for loader), and a driver in the front left of the hull beside the gun.

After October 1952, the crew was increased to 8 with an additional cannoneer, likely to increase the fire rate.

The crew communicated using an M238 flag set and, after October 1947, using 3 RC99 radios. There was an option to install a British No. 19 wireless set if 24 rounds of ammunition were removed.

Experiments

M37 with a Recoilless Rifle

Throughout 1945, the US launched a series of projects to develop vehicles that wielded a recoilless weapon. The first experiments on the M37 HMC chassis began in spring 1945, with the first project replacing the M2HB with a T21 75 mm recoilless rifle. The main disadvantage of this arrangement lay in the fact that the recoilless rifles had excessive backblast, which could injure the crew. This meant that the recoilless rifle could only be fired in certain directions to prevent the powerful exhaust blast from going into the vehicle due to the open top. In addition to this, these possible fire directions were not the most effective. The vehicle was canceled on 2 October 1947, being replaced by an M19 with four recoilless rifles instead of the anti-aircraft mount.

T38 Mortar Motor Carriage

The T38 was designed by the York Safe and Lock Company of York, Pennsylvania to provide a kit to convert the M37 to a mortar carrier, possibly to extend the life of the M37. The plans were then transferred to Detroit Arsenal, where one was converted and taken to Aberdeen Proving Ground in December 1945. The trials lasted until 1949, but the vehicle was not accepted into production, as self-propelled mortars had fallen out of favor.

The T38 MMC had an M4 10.7 cm (4.2 in) mortar mounted instead of the howitzer. The howitzer opening was closed off, as the mortar fired through the open roof. The T38 was similar to the M21 Mortar Motor Carriage, as the mortar was installed in the fighting compartment and could be fired from within the vehicle or outside the vehicle using a baseplate. A beam was placed along the bottom of the hull at the rear to support the mortar. The weight was decreased to 17.5 tonnes (17.2 tons), and it carried 140 mortar rounds. The vehicle’s crew was reduced to six. These would have included an assistant mechanic to man the mortar with the other crew members. The ammunition was stored in the fighting compartment. The mortar used a screw rotation mechanism which gave 90º of traverse to either side. The elevation of the mortar had a range from 45º to 60º.

Service

The M37 entered service in 1945 likely around April or within the first six months, however, it was too late to be deployed in the Second World War.

The only limited US combat deployment of the M37 happened during the Korean War, which lasted from 1950 to 1953. There, they were used to support the infantry as mobile artillery and to attack enemy positions. The M37 served in the 58th Armored Field Artillery Battalion (a primarily black segregated unit until 16 October 1951 when it was integrated), which was attached to the 65th Infantry Regimental combat team; however, it was converted to use towed howitzers and redesignated the 58th Field Artillery Battalion on 10 November 1951. This meant that the M37 served in Korea for around a year; some areas the M37 fought were near the Imjin River and Han River.

The M37 also served with the US forces in West Germany, likely being there until around 1957, including with the 30th Field Artillery Group and the 3rd, 14th, 70th, 74th, 78th and 517th Armored Field Artillery Battalions.

The M37 likely started to exit service in the late 1950s, after the M52 entered service. It remained active with the National Guard and Reserve units until the early 1960s. The M37 was superseded by the M52, a turreted self-propelled gun based on the M41 light tank which offered better protection for the crew, particularly as it could be sealed if fighting in a dangerous environment, such as the one created by the envisioned use of nuclear or chemical weapons.

Other Users – Spain

Spain likely received 28 M37 HMCs (although some English-language sources, such as M24 Chaffee Light Tank 1943-85 state 36). The first three vehicles arrived on 7 January 1957 in the port of Cartagena. These went to the Regimiento de Artillería a Caballo nº19 (Horse Artillery Regiment No 19) of the División de Caballería ‘Jarama’ (Jarama Cavalry Division). An additional vehicle arrived in June, and the remaining 28 in 1958. Twelve of these were used to complement the existing ones at the Regimiento de Artillería a Caballo nº19 with four M37s per battery. Another twelve were given to the Regimiento de Artillería de Campaña nº13 (Field Artillery Regiment No 13). The Artillery Academy received the remaining 4 M37 for training.

After the Regimiento de Artillería a Caballo nº19 was dissolved, its M37s were transferred to the Grupo de Artillería de Campaña Autopropulsada XI (Self-Propelled Field Artillery Group XI). Similarly, the twelve M37s of the Regimiento de Artillería de Campaña nº13 were transferred to the Grupo de Artillería de Campaña Autopropulsada XII (Self-Propelled Field Artillery Group XII). Both the XI and XII belong to the Brigada Acorazada ‘Brunete’ (Brunete Armored Brigade). Around six survive in museums.

Surviving M37

Many M37 HMCs have managed to survive to this day.

US

The US has eighteen surviving M37, mostly in good condition, in the following locations:

• Georgetown, Massachusetts
• Vestal, New York (nicknamed “CarolAnn”)
• Fort Lee U.S. Army Ordnance Museum, Virginia (serial number 75)
• American Armored Foundation, Tank Museum, Danville, Virginia
• Liberty, North Carolina
• National Armor and Cavalry Museum, Fort Benning, Georgia (serial number 37)
• 3rd Infantry Division Museum, Fort Stewart, Georgia
• Georgia Army National Guard Armory, Savannah, Georgia
• Gainesville, Florida
• Institute of Military Technology, Titusville, Florida (previously exhibited in the World War II Vehicle Museum and Learning Center in Hubbard, Ohio)
• Carleton, Michigan
• Russell Military Museum, Russell, Illinois
• US Army Artillery Museum, Fort Sill, Oklahoma (came from Fort Drum and arrived in 1966)
• Russell Military Museum, Russell, Illinois
• American Society of Military History “Tankland”, South El Monte, California (incomplete)

Serial number 115 survives and was once at the John W. Rich Auto Museum, Reading, Pennsylvania, but was likely sold to an unknown buyer in 2014.

Spain

Five M37s survive in Spain: one in El Goloso Museum (Madrid) and four at various locations in Zaragoza.

Conclusion

The M37 emerged as an improved artillery platform, born out of the necessity for a lightweight, high-speed mobile solution to replace its predecessor, the M7 Priest. Through meticulous development and rigorous testing, the M37 evolved into a useful tool which was too late to serve in World War 2, but served in the Korean War, boasting a blend of firepower, mobility, and crew protection. Over time, the M37’s role continued beyond wartime theaters, serving in West Germany and continuing its duty with National Guard and Reserve units well into the early 1960s. Internationally, the M37 found a new home in Spain, where it contributed to their artillery regiments.

M37 Specifications
Dimensions (LxWxH)	Length: 5.49 m (6 yd) Width: 3 m (3.28 yd) Height: 2.84 m (3.11 yd)
Track width	T72: 40.6 cm (16 in) T85E1: 35.6 cm (14 in)
Total Combat Weight	25 tonnes (23.1 tons)
Crew	Originally 7 Later 8
Engine	two 16-cylinder Twin Cadillac Series 44T24 220 hp
Maximum speed	56 km/h (35 mph)
Suspension	Torsion bar
Range	161 km (100 mi)
Armament	105 mm M4 howitzer .50 caliber M2HB machine gun
Armor	9.53 mm (0.375) to 12.7 mm (0.5 in)

Sources

E J Zawadzki (compiled by), Development History of 105mm Gun Howitzer Motor Carriages and 25-pdr Gun Motor Carriage, Office of the Chief of Ordnance, 9 March 1945
FM 6-76: Service Of The Piece 105mm Howitzer Motor Carriage, M37, War Department, 15 April 1945
TM 9-1901 ARTILLERY AMMUNITION, WAR DEPARTMENT, 29 June 1944

RP Hunnicutt, Stuart – A history of the American light tank, Presidio Press, Novato, 1992
Steven J. Zaloga, 077 – M24 Chaffee Light Tank 1943-85, Osprey Publishing, New York, 2003
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Jim Mesko, Armor in Korea A Pictorial History, Squadren /Signal Publications inc, Carellton, 1984
Francisco Marín Gutiérrez & José Mª Mata Duaso, Carros de Combate y Vehículos de Cadenas del Ejército Español: Un Siglo de Historia (Vol. II) (translated: Tanks and Chain Vehicles of the Spanish Army: A Century of History (Vol. II)), Quirón Ediciones, Valladolid, 2005

Donald W Boose Jr, US Army Forces in the
Korean War 1950 – 53, Osprey Publishing, Oxford, 2005

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