155 mm gun motor carriage M40
Self Propelled Gun - 311 produced 1945.
Development of the M40 Gun Motor Carriage
Before the M40 was an earlier vehicle projected as a way to make mobile the 155 mm 1918 heavy field gun manufactured in 1918. This led to the design of the T6 GMC built and tested in early 1942. 100 were ordered when standardized by late 1942. The success of the 155 mm M12 GMC was relative to the chassis, which appeared overwhelmed. Only 100 M12 were manufactured by Pressed Steel Car Company between September 1942 and March 1943. It used the chassis of the M3 Grant tank but in operations, the recoil itself almost destroyed the suspensions. Most were later reconverted as armoured supply vehicles for the M40, named the M30 cargo carrier, initially paired with each M12 to carry extra rounds (40). It was mostly used in the assault of German fortifications in Italy and France after D-Day notably the Siegfried Line. Its 1918 gun was also perfectible.
The shotcomings of the M12 led in late 1942 already to plan a successor, the M40, designed on a late-war M4A3 Sherman chassis and with the 155 mm gun M1, successor to the 155mm M1918. The prototype designation was the T38, and it was tested in 1944. The first pilot was completed on 28 July 1944, tested at Aberdeen Proving Grounds. Soon after the 4th and 5th pilots were completed as the T89, 8in Howitzer Motor Carriage, prototypes for the M43 HMC. The 2nd and 3rd T83 were completed in October and were used for tests at the Field Artillery Board at Fort Bragg. Designation was changed to the M40 in March 1945, but production started a month earlier.
A single pilot vehicle was then sent to the European Theatre in 1945, deployed by the 991st Field Artillery Battalion, which also tested a 8-inch howitzer motor carriage T89 (future M43 HMC). Results were very positive and 600 were ordered to the same company that made the M12, Pressed Steel Car Company. However only 311 were completed by the at the end of the war when the order was cancelled. 24 of the late batch were converted postwar into M43s. Most of the production vehicles saw action in the Korean War.
Design of the M40 GMC
The "155 mm gun motor carriage, M40" simplified as M40 GMC, was a self-propelled artillery setup on a widened and lengthened medium tank M4A3 chassis. There was one more axle, and the drive sprocket and idlers were pushed further forward and aft, and to compensate for the weight inscreas, a Continental engine was installed. The last point was was the installation of the late war improved HVSS (horizontal volute spring suspension). The vehicle weighted 81,000 lbs (37,000 ton), and was measuring 280.4 inches or 7,12 meters without the gun, which protruded forward 68 inches or 1.70m. The vehicle was 124 inches or 3,15 meters wide, and 130 inches or 3,30 meters tall, gun lowered in travel lock forward. At max angle it was around 4.5 meters or more.In terms of layout, the M40 GMC recalled the 155mm GMC M12. It had the engine relocated to the middle, with the driver and co-driver at the front, each having a late M4A3 turret cupola with manoramic view. The transmission was located between them and at in nose. The final drive and differential housing was angled forward to make up for the steeper slope of the propeller shaft after moving the engine forward. Behind this mid-hull engine compartment enclosed by fireproof bulkheads on each side, was located the main casemate supporting the ordnance. It had walls tall enough to protect the gun crew of six, commander, left gunner, right gunner and three loaders.
The rear combat compartment comprised a base mount, a chassis, and seen from the rear, on the right and left were located universal ammo racks, and folded gun crew seats on both sides as well. Stowage boxes were located on the floor, and went down to the chassis's torsion bar floor. There were air cleaners on both sides of the main gun, which was assorted with a traversing handwheels to the left and elevating handweel/clutch on the right and elbow telescope for the gunner seated to the right, protected by a folded shield. On the left was located a winch crank handle and cable to fold down the rear spade and wall enclising the space, forming a platform to walk on for loaders. There was also a portable fire extinguisher. Optionally, frames could be installed forward and at the rear of the box to hoist a protective tarpaulin above, espcially useful in winter.
Protection of the M40 GMC
If the M4A3 chassis was well protected with a Rolled and cast homogeneous steel all welded hull, but the rear compartment was open to the elements and shrapnel, and only the walls provided some degree of lateral protection, plus the folded shields forward only for the gun operators. The Upper front was protected by 0.5 inches (1.3cm) sloped at 58°, the lower front at 4.25 inches down to 2 inches (10.8cm to 5.1cm) at 46° for the latter. The open compartment's upper sides were protected against machine gun fire at 0.5 inches (1.3cm) and the lower sides at 1 inch (2.5cm). The rear wall was 0.5 inches (1.3cm), front floor 1 inch (2.5cm), rear floor 0.5 inch (1.3cm) and the gun shield was 0.5 inch thick (1.3cm) at roughly 45° since it was shaped like an "S". It was not rare also to bury the vehicle in prepared holes and stack sandbags around.Mobility
The M40 was powered by a Continental R975 C4; 9 cylinder, 4 cycle, static radial, supercharged gasoline. It was coupled wth a Synchromesh, 5 speeds forward, 1 reverse gearbox and steered by classic differencial levers. Brakes used a simple mechanical external contracting system. Performances were 400 hp at 2,400rpm and gross 460 hp at the same rev, for a torque of 940 ft-lb at 1,700rpm or 1025 ft-lb gross. This provided a top speed on flat of 21 mph/34 kph sustained and 24 mph/39 kph in a dash. 39kph dash.The M40 GMC had a Ground clearance of 17 inches (43cm), and a track tread of 101 inches or 2,57m. Ground pressure on hard pavement was 10.7 psi or 0.751kg/cm². The drivetrain comprised three bogies with horizontal volute spring, each with dual wheels and dual track pin, 2 dual and 3 single track return rollers, a 13-tooth front drive and dual wheel rear idler, adjustable. Schok absorbers were located on each bogie. Fuel capacity was 215 gallons or 814L, for a cruising range of roughly 100 miles or 160km on roads. The vehicle was field tested, and showed able to clmb a 60% grade, with a turning diameter of 83 feet or 25 m. It could cross a 92 inches or 2.30 m trench, climb a 24 inche sor 61 cm wall, and ford up to 40 inches or 1m of water without preparation.
Armament
The centerpiece of the design was its 155mm Gun M1A1 or M2 installed on an M13 mount at the rear of the chassis. Traverse was 36° (18° left and right) and elevation +45° to -5°, all manual. 20 rounds were carried, also manual loading. It came with the Panoramic telescope M12 or M12A7C, telescope M69F for the chief gunner and elbow telescope M16A1F for the cannoneer. The legendary "long tom" was a beast of a gun, a replacement for the French WWI Canon de 155mm GPF. It could fire a 100 lb (45 kg) shell to a range of 14 mi (23 km) and estimated accuracy life of 1,500 rounds.Rate of fire was about 40 rounds per hour, meaning without supply, the M40 would ran of ammunition after just 30 minutes. Muzzle velocity was 853 m/s (2,799 ft/s). Rounds were in separate casing, APBC/HE M112 with AP capabilities against armour, 45 kgs explosive D or HE M101 with 43 kg TNT. It could also fire smoke and chemical shells. When used in direct fire against armur, the AP M112 Shell could penetrate a 30° sloped 160mm plate at 457m or 500 yards and 152 mm (8 inches) at 914 m or 1000 yards of face hardened armour. There was no secondary armament or defensive ones apart the troop's own personal small arms. At 23 km range behind the frontline it was deemed unecessary. There was not even a ball mount LMG.
Variants, T38 chassis:
M43 SPH
Cargo carrier T30: several pilots but production cancelled in December 1944.
8-inch howitzer motor carriage M43: 8 inches (203 mm) HMC, standardized August 1945: 48 built
250 mm mortar motor carriage T94 10 in (250 mm) MMC, design started in February 1945, single prototype completed 1946. Not adopted.
M40 GMC specifications | |
| Dimensions (L-w-H) | 9.1 x 3.15 x 2.7 m (29 ft 10 in x 10 ft 4 in x 8 ft 10 in) |
| Total weight | 36.3 metric tons (80,000 lb) |
| Crew | 8 (Commander, driver, 6 gun crew) |
| Propulsion | Wright Continental R975 EC2 340 hp (253 kW) p/w 9.36 hp/t |
| Top speed | 38 km/h (24 mph) on road, 23 km/h (14 mph) off-road |
| Suspensions | HVSS (Horizontal Volute Spring Suspension) |
| Range | 170 km (106 mi) |
| Armament | 155 mm M2 gun, 20 rounds |
| Armor | 12 mm (0.5 inches) |
The M40 Gun Motor Carriage in action
As deployed in Korea
One of the T83 pilots arrived in France for combat tests with the Zebra mission, with a T89 and a few Pershings. The SPGs ended at the 991st Field artillery Battalion and the 8in howitzer of the second was replaced by a 155mm gun. They took part in the battle for Cologne. The T89 later had its howitzer restored. It was clear that the open fighting compartment left the gun crews exposed in urban combat. General Barnes suggested an armour and secondary machine gun and if later at home a light armoured cab was designed it was considered too unwieldy for the gun crew to operate and was not adopted.
The vehicle was only standardized in November 1945 and as the war long ended in Europe, it also just ended in Asia. The ones produced were thus mothballed, with one kept for further evaluation. They could had been scrapped after ten years, but the Korean war broke up. Thus after World War II, the M40 was used not only by the US Army but also the British Army in Korea. The later designated it "155 mm SP, M40 Cardinal". The naming was to keep the ironic tradition of ecclesiastical names for self-propelled (SP) artillery. In Korea, the M40 was deployed tactically by Gun sections of one M40 GMC and one M4A1 high speed tractor for towing it and a 4-wheel, 8-ton M23 ammunition trailer. Each battery commrised four gun sections, each with the M40, the M4A1 with M23 ammo trailer. The latter were replaced by the M30 cargo carrier.
The M40 saw action indeed in 1950-53, espcially when the war became more static in Jan-Feb. 1951. Artillery came back with a vengeance, and the three hundred M40s available were deployed in several actions such as the retreat cover of Chosin reservoir, and generally all defensive actions of 1951-53, the gruelling and long stalemate on the 38th Parallel. The M40, alongside the closely related M48, were kept in reserve until 1960. Others were sent in between to the british Army which used some "east if suez" and in had some deployed in Germany.
Gallery
"Courageous Confederate" 937th Field Artillery Battalion of the Arkansas National Guard, Korea 1950
"Big Bruiser" Battery B, 937th FAB, U.S. 8th Army, Korea, 1953.
Read More/Src
Books
M40 Gun Motor Carriage and M43 Howitzer Motor Carriage in WWII and Korea (Legends of Warfare: Ground): 2 Hardcover – Illustrated, 28 Oct. 2017, by David Doyle (Author)Hunnicutt, R.P. Sherman: A History of the American Medium Tank. Navato, CA: Presidio Press, 1994.
Doyle, David. M40 Gun Motor Carriage and M43 Howitzer Motor Carriage in WWII and Korea. Atglen, PA: Schiffer Publishing, Ltd., 2017.
TM 9-747 155-mm Gun Motor Carriage T83 and 8-inch Howitzer Motor Carriage T89. Washington, DC: War Department, 26 February 1945.
TM 9-747 155-mm Gun Motor Carriage M40 and 8-inch Howitzer Motor Carriage M43. Washington, DC: War Department, 15 September 1947.
TM 9-1747 Ordnance Maintenance--155-mm Gun Motor Carriage M40 and 8-in. Howitzer Motor Carriage M43 Hull and Suspension, ORD 9 SNL G-232 List of All Service Parts for Carriage, Motor, 155-mm Gun, M40 and Carriage, Motor, 8-in Howitzer, M43. TM 9-2300 Artillery Matériel and Associated Equipment. Washington, DC: Department of the Army.
Chamberlain, Peter, and Chris Ellis. British and American Tanks of World War Two. Cassell & Co., 2000.
Siemers, Cary. "USA's Self Propelled Guns." World War II Tanks & Vehicles and Advanced Squad Leader.
Links
Full specs on afvdb.50megs.comen.wikipedia.org
Photos on afvdb.50megs.com
historyofwar.org/
digital.library.unt.edu: 155-mm gun motor carriage M40 and 8 in. howitzer motor carriage M43 hull and suspension manuals, 1947.
panzerserra.blogspot.com
David Doyle book on amazon
militaryfactory.com
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