Welcome to the suggestion post for the M40 GMC! This is an American self-propelled artillery vehicle, mounting the 155mm M2 “Long Tom” field gun. While it can fire a devastating M101 HE round, it can also fire an APBC-HE round known as M112. In-game, this shell would penetrate about 246mm of homogenous armor at 0°, as calculated by Gaijin’s calculator. Needless to say, the M40 GMC can certainly pack a punch against anything unfortunate enough to be hit by it. However, despite being an M4A3 Sherman chassis, the armor in most parts will only have enough protection against light machine guns, meaning the commander of the vehicle probably shouldn’t get too close to the action. Owing to the large gun, there is limited ammunition, and the time to reload will take longer than lower caliber guns found on most tanks, so the crew will have to make their shots count!
Men of the 991st Field Artillery Battalion manning M12 GMCs at Bildchen, Aachen, 1944. This particular battalion is a key element of the M40 GMC’s story, as you’ll find out later.
After it entered World War 2, the United States brought to war some of its latest weapons, one of which was the M12 Gun Motor Carriage. Built on a Medium Tank M3 chassis, the M12 GMC mounted a 155mm field gun, derived from the famous French 155mm GPF from the World War 1 era. However, one problem the U.S. Army faced throughout the war was a lack of supply of these guns. Even after its entry into service, there were no plans to replace the M12 GMC’s gun, despite the gun’s replacement, the 155mm Gun M1, nicknamed “Long Tom,” having entered service in 1938. Field Artillery Command didn’t see this as an issue, as they saw vehicles such as the Mack NO truck and later the M4 High-Speed Tractor as sufficient for towing the 155mm M1. Their minds were changed in 1944 when it was realized that the Army would need something mobile with enough firepower to break through the Siegfried Line. On March 9th, 1944, the Ordnance Committee recommended the development of a new self-propelled gun armed with the 155mm Gun M1.
At first, it was thought that mounting this gun on the M12 chassis would be sufficient, but studies showed that the M12 was wholly unsuitable for the M1 field gun. Further analysis showed that while the M3 tank was unsuitable as a chassis, the Medium Tank M4 was. This was ideal, as the M4 tank by 1944 was being produced in large quantities, simplifying logistics and production. The Ordinance Committee then authorized the start of work on the new project, designated Gun Motor Carriage T83.
The first 155mm GMC T83, bearing the name “Big Shot”, which may be familiar to War Thunder players!
The work on developing the T83 GMC was given to the tank-automotive plant in Detroit, and the Pressed Steel Car Company in Pittsburg, who was responsible for the M12 GMC. Due to the expected increase in weight, the T83 was to use a Sherman chassis fitted with horizontal volute spring suspension from the outset. On top of this, the vehicle would use the 580 mm / 23 inch T66 metal tracks, and the hull would be lengthened and widened. Despite these changes, the vehicle’s layout followed that of the M12 GMC, with the fighting compartment and gun located at the rear and the driver and his assistant at the front. With the design complete, the Ordinance Committee submitted a contract to the Pressed Steel Car Company for five prototypes and five ammunition carriers to accompany the vehicle.
The T89 HMC, note that it is still the chassis named “Big Shot” as before, but is fitted with a larger 203mm / 8-inch M1 howitzer.
The pilot vehicle was finished on July 28th, 1944, and the T83 performed extremely satisfactorily when tested at Aberdeen Proving Ground. After firing 200 rounds, it was concluded that the platform was sufficiently stable at all elevation ranges with and without the use of the spade. After testing with the 155mm, the vehicle would be fitted with the 203 mm M1 howitzer, which would fire 75 rounds, and be redesignated as the 8-inch howitzer motor carriage T89. Two further T83 GMCs were completed in October and sent to Fort Bragg for a month of intense testing. After the conclusion of this round of testing, several modifications were suggested, and introduced. Pilot #2 was sent to Aberdeen, with Pilot #3 being sent to the Lima Tank Plant for overseas shipment. Before production began, it was decided in January of 1945 to send one T83 GMC and one T89 HMC to Europe after modification. Pilot #3, sent to Lima Tank Plant, was chosen to represent the T83, while one of the two T89s produced that month was selected to accompany it. These two would arrive in Europe in February, just as Pressed Steel Car Company began delivering its first production T83 GMCs.
One of the two pilot vehicles in a firing position near a wrecked Junkers Ju-87 near Burbach, Germany, 1945.
After they arrived in Europe, the T83 and T89 were attached to the United States Army’s Ordinance Department’s “Zebra” Mission, which also saw the combat debut of the T26E3 Heavy Tank. The T83 and T89 were attached to the 991st Artillery Battalion, fighting as part of the 3rd Armor Division. Soon after, the 991st replaced the T89’s 203mm M1 howitzer with the 155mm M1 for uniformity, essentially converting the T89 into a T83. The vehicles were often used for infantry support, and thanks to their elevation angles, they could be used for direct fire and their intended indirect fire role.
Following the end of the Zebra Mission, General Barnes directed Aberdeen to study the addition of extra armor protection and secondary armament. Since Pilot #3 was off fighting in Europe, Pilot #2, which had been sent to Aberdeen, was fitted with a ball-mounted .30 caliber M1919 machine gun at the front of the assistant driver’s position, as on standard M4 Shermans. In addition, a further two machine guns were put at each rear corner of the vehicle, tests of which proved that these provided excellent coverage. Another machine gun was fitted to the gun shield, but this didn’t pan out due to the limited traverse. Further armament options were explored, such as the 57mm and 75mm recoilless rifles, but these proved difficult and dangerous to fire from the vehicle due to the backblast. Aberdeen recommended that if armament larger than the .30 caliber was required, the .50 caliber M2 be used. For further protection, several wooden mockup cab protection options were tested, but these ultimately didn’t make it to production vehicles.
In Europe, the converted T89 had a significant role as the first artillery piece to fire on German positions in Cologne on February 27th, 1945. Later, the 991st Artillery Battalion put the 203mm M1 howitzer back on the converted vehicle and would see action until the war’s end in Europe. Praise from their crews, and no doubt the infantry it supported, was noted back in the United States, and would impact the number of vehicles planned for production. In May of 1945, the T83 was officially standardized as the 155 mm Gun Motor Carriage M40, with an order for 308 being placed in July.
M40 Gun Motor Carriages of Battery B, 937th Field Artillery Battalion, providing fire support to the U.S. Army 25th Infantry Division, Munema, Korea, November 26th, 1951.
It wouldn’t be long after the war before the M40 GMC was again called into action. On June 25th, 1950, Korean People’s Army forces crossed the border into South Korea, kicking off what would be known as the Korean War. The United Nations Security Council was quick to condemned the invasion. From this, the United Nations Command was formed, with forces authorized to be sent to the Korean Peninsula to push back the attack. Most of the UN force sent to aid the South Koreans were American troops, which were armed with the M40 GMC in larger numbers. In Korea, the M40 GMC would be the mainstay of American artillery and, as it did in World War II, support infantry, directly or indirectly. By the time of the Korean War, most M40 GMCs had T80 or T84 tracks instead of the T66 tracks used previously.
By the 1950s, several M40s had been sent to the UK and France. With the UK, they would serve with the British Army of the Rhine until the mid-1960s and with France until 1972. With the United States, it would be replaced in the following decades with more advanced artillery but be remembered as a powerful and effective heavy artillery piece. Today, there are 10 M40 GMCs remaining, 7 in the United States, 2 in the UK, and one in Germany.
An M40 GMC at the 3rd Cavalry Museum, Fort Hood, Texas.
- Weight: 36.3 metric tons
- Length: 9.1 m
- Width: 3.15 m
- Height: 2.7 m
- Crew: 8 (Commander, driver, 6 gun crew)
- Armor: 12 mm
- Main armament: 155 mm M2 gun
- Ammunition carried: 20 rounds
- Traverse: 36° (18° left and right)
- Elevation: +45° to -5°
- Engine: Wright Continental R975 EC2, 340 hp
- Power/weight: 9.36 hp/t
- Suspension: HVSS (Horizontal Volute Spring Suspension)
- Operational range: 170 km
- Speed: 38 km/h on road & 23 km/h off road
- Hunnicutt, R. P. (1994). Sherman: A History of the American Medium Tank. Presidio Press. ISBN 0-89141-080-5
- Ness, Leland (2002). Janes World War II Tanks and Fighting Vehicles. Harper Collins. ISBN 0-00-711228-9
- TM 9-747 155-mm Gun Motor Carriage T83 and 8-inch Howitzer Motor Carriage T89, 1945-02-26
- TM 9-747 155-mm Gun Motor Carriage M40 and 8-inch Howitzer Motor Carriage M43, 1947-9-15
- Doyle, David. Late War U.S. Tanks The M26 Pershing, M24 Chaffee and M40 SPG. Letterman Publications, 2005.
- Tank Archives: Once More on a New Chassis
- 155mm GMC M40