The M10 tank destroyer, formally known as the 3-inch gun motor carriage M10 or M10 GMC, was an American tank destroyer of World War II. After US entry into World War II and the formation of the Tank Destroyer Force, a suitable vehicle was needed to equip the new battalions. By November 1941, the Army requested a vehicle with a gun in a fully rotating turret after other interim models were criticized for being too poorly designed. The prototype of the M10 was conceived in early 1942 and delivered in April that year. After appropriate changes to the hull and turret were made, the modified version was selected for production in June 1942 as the "3-inch Gun Motor Carriage M10". It mounted the 3-inch (76.2 mm) gun M7 in a rotating turret on a modified M4 Sherman tank chassis.
It was built in two variants. The M10 GMC used the M4A2 Sherman chassis, and the M10A1 used the M4A3 chassis. Production of the two models ran from September 1942 to December 1943 and October 1942 to November 1943, respectively.
The M10 was numerically the most important U.S. tank destroyer of World War II. It combined thin but sloped armor with the M4's reliable drivetrain and a reasonably potent anti-tank gun mounted in an open-topped turret. Despite its obsolescence in the face of newer German tanks like the Panther medium tank and the introduction of more powerful and better-designed types as replacements, the M10 remained in service until the end of the war. During World War II, the primary user of the M10 tank destroyer was the United States, but many were supplied under Lend-Lease to the United Kingdom, Canada and Free French forces. Several dozen were also sent to the Soviet Union. Post-war, the M10 was given as military surplus to several countries, such as Belgium, Denmark, and the Netherlands, through the Mutual Defense Assistance Act or acquired through other means by countries like Israel and the Republic of China.
The M10 is often referred to by the nickname "Wolverine", an unofficial name that sometimes appeared in wartime Chrysler advertising, but that was not used by U.S. troops;Zaloga (2002), author's note the M10 was never officially assigned a nickname or referred to with one when used by American soldiers, who simply called it a "TD" (a nickname for any tank destroyer in general) beyond its formal designation.Bryan Perrett (2003), Impossible Victories, p 98, Barnes & Noble, Chris Henry & Brian Delf (2004), British Anti-tank Artillery 1939–45, p 23, Osprey, .
Doctrine U.S. combined arms doctrine on the eve of World War II held that tanks should be designed to fulfill the role of forcing a breakthrough into enemy rear areas. Separate GHQ (General Headquarters) tank battalions would support infantry in destroying fixed enemy defenses, and armored divisions would then exploit the breakthrough to rush into the enemy's vulnerable rear areas. U.S. tanks were expected to fight any hostile tanks they encountered in their attack, but the mission of destroying massed enemy armored thrusts was assigned to a new branch, the Tank Destroyer Force developed in 1941. Tank destroyer units were meant to counter German blitzkrieg tactics. Rather than rely on a "thin cordon" of anti-tank guns which would be defeated by a concentrated attack, the tank destroyer units were to be held as a reserve behind the battleline (at the corps or army level), and were to move quickly to the site of any massed enemy tank breakthrough.Steven J Zaloga M10 and M36 Tank Destroyers 1942-53 Osprey They would maneuver aggressively and using ambush tactics to destroy enemy tanks; charging or chasing enemy tanks was explicitly prohibited. This led to a requirement for very fast, well-armed vehicles. Though equipped with turrets (unlike most self-propelled anti-tank guns of the day), the typical American design was more heavily gunned, but more lightly armored, and thus more maneuverable, than a contemporary tank. The idea was to use speed and agility as a defense, rather than thick armor, to bring a powerful self-propelled gun into action against enemy tanks. Or more precisely, to use speed to deploy ahead of the attacking enemy, take up camouflaged and protected firing positions on their flanks if possible, and then open fire. If unable to destroy the enemy force or to force them to retreat, then mobility would be used to avoid enemy fire until the TDs could withdraw, preferably to move up and deploy for another ambush. Direct combat in the open against tanks was to be avoided whenever possible.
Development After the formation of the Tank Destroyer Tactical and Firing Center at Camp Hood, Texas in November 1941, the Army began testing to standardize on a configuration for the new tank destroyer battalions. The Tank Destroyer board began to examine several hundred Ordnance Department prototype proposals for a tank destroyer mounting a 3-inch gun, initially focusing the most interest on two:
The T1, developed beginning in 1940 and standardized as the "M5 3-inch Gun Motor Carriage" in January 1941. It was a modified Cleveland Tractor Company airfield towing tractor mounting a development of the 3-inch gun M1918 anti-aircraft gun in a limited-traverse mounting. T24, developed beginning in October 1941. It was an M3 Lee chassis mounting a 3-inch gun M1918 in a limited-traverse mounting. The T24 was initially rejected as being too tall and the T40 was its improved derivative. The T40 was standardized as the "M9 3-inch Gun Motor Carriage" for limited production in May 1942 but never built.
Meanwhile, as the final design developments of these two tank destroyers were underway, the Ordnance Department became dissatisfied and in November 1941 issued an additional specification for a tank destroyer with a 3-inch gun in a rotating turret. Design work began immediately. The 3-inch Gun Motor Carriage T35 combined an early-production M4A2 medium tank hull with the 3-inch gun M7 (also derived from the M1918 gun) from the M6 Heavy Tank in a cast, circular, open-topped turret. Using lessons learned from combat reports from the Philippines, the armor on the sides and rear of the upper hull was changed from flat to sloped plates. This new test vehicle was designated the 3-inch Gun Motor Carriage T35E1. Prototypes of these two vehicles were delivered to Aberdeen Proving Ground in April 1942, and the Army selected the T35E1 for further development on 2 May 1942.Zaloga (2002) p7 The side and rear upper hull armor of the T35E1 was reduced from 1 inch (25 mm) to 0.75 inches (19 mm) in order to reduce the weight of the vehicle. The staff at Aberdeen Proving Ground was worried that the armor of the T35E1 was too thin, and so bosses for appliqué armor panels were added to the hull sides, glacis, and turret sides. As the cast turret was found to be difficult to manufacture, the design of the turret was changed to a sloped pentagonal shape made of welded armor plate.Zaloga (2013) p25 In June 1942, the modified T35E1 was standardized as the 3-inch Gun Motor Carriage M10. By fall 1943, with its M5 and M9 competitors being eliminated from the design competition and their production contracts cancelled, the M10 was to become the United States' primary tank destroyer of the early war period.
As there were fears that the production of M4A2 chassis would be inadequate for M10 production, an alternate design, the 3-inch Gun Motor Carriage M10A1 based on the M4A3 medium tank chassis, was also authorized for production.
Design
American tank destroyer doctrine emphasized speed and gun power over armor. As a result, the M10's armor was thin, which made it vulnerable to most German anti-tank weapons. The thickness of the M10's armor ranged from . The lower hull, being modified from that of a standard M4A2 or M4A3 Sherman tank, had armor on the sides and rear, and a floor. The rounded, cast transmission cover was thick. In a departure from its M4 Sherman parent, the M10 lacked the extra -inch floor plate under the driver's and assistant driver's stations that provided them additional protection from mines.
The glacis plate was thick, sloped at 55 degrees from the vertical. The sides and rear of the upper hull were thick, sloped at 38 degrees from the vertical. The rear upper hull plate was used for storage of the vehicle's pioneer and maintenance tools: a axe, a crowbar, a mattock handle and head, a double-sided sledgehammer, and a track tensioning wrench. The sides and rear of the upper hull featured angled extensions or covers over the upper run of track. These extensions often got in the way of fitting "duckbill" extended end connectors, used to reduce ground pressure on soft ground, and were often removed, along with the front fenders, by maintenance units. The hull roof plate ranged from thick over the driver's and assistant driver's stations and turret ring, to thick over the engine compartment.
The manually rotated turret of the M10 was a pentagonal shape. The sides were sloped 15 degrees inward from the vertical and were thick. The rear of the turret was also 1 inch thick. The partial roof on the front third of the turret opening was thick. The triangular cast gun shield sported the thickest armor on the vehicle, . It was sloped at 45 degrees from the vertical and horizontal.
The M10 and M10A1 were mechanically identical except for their power plants. The M10 used the General Motors 6046, a twin engine formed from two Detroit Diesel 6-71 inline engines mated to a single output. The tandem engine produced at 2,100 rpm. One advantage of the GM 6046 was that the engines could be disconnected at will from the output and run independently. If one of the engines was damaged or destroyed, it could be disconnected and the other engine used to move the vehicle. The engine of the M10A1 was the Ford GAA, an 8-cylinder derivative of an ill-fated V-12 aircraft engine project. It produced at 2,600 rpm. When tested side by side in September 1943, the M10A1 was judged to have superior automotive performance to the M10. Even though it produced only slightly less torque, the M10A1's engine was far lighter, and used a common fuel like the rest of the Army's vehicles (gasoline). By the time the test results were released in February 1944, the Army was committed to using the M10 overseas. As a result, the M10A1 was kept in the United States for training.
The M10 and M10A1 had a crew of five; commander, gunner, loader, driver, and assistant driver. The driver and assistant driver (who also operated the vehicle's radio) were seated in the front hull and provided with periscopes. The unique design of the hull hatches to clear the gun mantlet meant that the driver's view directly to the left side was obstructed. He was provided with a second periscope at the edge of the hull for this purpose. The commander, gunner, and loader were all located in the turret. The commander sat on a folding seat at the right rear. The gunner, on the left side of the gun, normally stood to operate it, but he was also provided with a folding seat. The loader normally stood in the area behind the gun. A third folding seat was provided in the turret for the assistant driver in case he needed to assist the loader for any reason.
Unlike the M4 tanks it was based upon, the M10 lacked an auxiliary generator, which forced the crew to run the main engines in order to recharge the vehicle's batteries. The engine noise and smoke could attract enemy fire, especially in close quarters, where the M10 was vulnerable due to its thin armor and open-topped turret. The lack of an auxiliary generator was rectified with the introduction of the M36 tank destroyer.
Production