M10 tank destroyer

The M10 tank destroyer, formally 3-inch Gun Motor Carriage, M10 was a United States tank destroyer of World War II based on the chassis of the M4 Sherman tank. It was numerically the most important U.S. tank destroyer of World War II and combined a reasonably potent anti-tank weapon with a turreted platform (unlike the previous M3 GMC, whose gun was capable of only limited traverse). Despite the introduction of more-powerful types as replacements, it remained in service until the end of the war. Some of those replacements were in fact modified and/or rebuilt from the M10 itself.

It was christened the Wolverine by the British, although unlike other vehicle names such as the M4 Sherman, the name was not adopted by American soldiers, who called it TD (a nickname for any tank destroyer in general) beyond its formal designation.

Development
US combined-arms doctrine on the eve of World War II held that tanks should be designed to fulfill the infantry support and exploitation roles. The anti-tank warfare mission was assigned to a new branch, the tank destroyer force. Tank destroyer units were meant to counter German blitzkrieg tactics. Tank destroyer units were to be held as a reserve at the corps or army level, and were to move quickly to the site of any enemy tank breakthrough, maneuvering aggressively to destroy enemy tanks. This led to a requirement for very fast, well-armed vehicles. Though equipped with turrets (unlike most tank destroyers 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.

The 3-inch Gun Motor Carriage T35 was the prototype of the M10. It was equipped with a 3-inch (76.2 mm) gun in a new sloped, circular, open-topped turret, developed from the Heavy Tank T1/M6 turret, and mounted on an early-production Medium Tank M4A1 hull.

This prototype was further developed by sloping the hull, using an M4A2 chassis, and replacing the circular turret with a pentagonal version; this model was designated 3-inch Gun Motor Carriage T35E1. In June 1942 the T35E1 was finalized as the 3-inch Gun Motor Carriage M10 and ordered into full production. Towards the end of production the 76 mm gun M1 was installed in the last 300 or so M10s, as it was being fitted into the new production M4 Sherman tank at the time. The 76 mm M1 offered slightly better anti-armor performance than the previous 3" gun M7.

A British variant, designated "17pdr SP Achilles", was developed by mounting the successful 17-pounder anti-tank gun in a modified turret. The 17-pounder was of a similar bore, but had far superior armor penetration capability. It was used by the British, Canadian and Polish armies in Italy and northwest Europe.

After World War II, a batch was acquired by the Republic of China Army as demilitarized surplus items. The vehicles' main guns were rendered useless prior to delivery and consequently replaced in 1949 with ex-Imperial Japanese Army 105mm infantry howitzers.

Production
Production of 4,993 M10s and 375 M10A1s ran at General Motors' Fisher Tank Arsenal in Grand Blanc, Michigan from September 1942 through December 1943. Ford Motor Company built 1,028 vehicles of the M10A1 variant from October 1942 until September 1943. Fisher also built 300 M10A1s without turrets, which were later converted to M36 tank destroyers.

Armament
The M10 used a Medium Tank M4A2 chassis (M10A1s used M4A3 chassis) with an open-topped turret mounting a 3" gun M7. This gun fired the Armor Piercing M79 shot that could penetrate 3 inches of armor at 1,000 yards at 30 degrees from vertical. Other ammunition carried throughout its service life included the Armor Piercing Capped Ballistic Cap (APCBC) M62 projectile, High Velocity Armor Piercing (HVAP) M93 shot, and Armor Piercing High Explosive (APHE); 54 rounds of 3-inch ammunition were carried. The rear of the turret carried two large counterweights which gave it a distinctive shape. The main shortcoming of the 3 inch cannon was its APHE round, which was the round most commonly used for engaging tanks. The 3 inch APHE round was based on the naval 3 inch round and had a small charge in the rear of the round which was supposed to explode after penetration of the target's armor plating. Unfortunately it was discovered that it exploded on impact or shortly thereafter, causing the round not to penetrate. It is still a puzzling mystery as to why this problem was never addressed with a better base fuse or by deleting the small HE charge in the rear of the round. This was also the problem with the towed version of the 3 inch cannon, the M-5, in the antitank role.

A .50 in (12.7 mm) Browning M2HB machine gun could be mounted on the top rear of the turret for use against enemy infantry and for anti-aircraft use, along with 1000 rounds. The crew were also equipped with their personal weapons for self-protection.

Combat use
In its combat debut in Tunisia in 1943 during the North African campaign, the M10 was successful as its M7 3-inch gun could destroy most German tanks then in service. The M10's heavy chassis did not conform to the tank destroyer doctrine of employing very light high-speed vehicles, and starting in mid-1944 it began to be supplemented by the 76mm Gun Motor Carriage M18 "Hellcat". Later in the Battle of Normandy, the M10's gun proved to be ineffective against the frontal armor of the newer German Tiger and Panther tanks unless firing HVAP rounds, but was effective against the most common tanks such as the Panzer IV medium tank and other lighter vehicles and self-propelled guns. Tank destroyer units had been supplemented with 90mm towed guns in partial anticipation of heavier German tanks, but their lack of mobility made employing them difficult. By the fall of 1944, the improved 90mm Gun Motor Carriage M36 began to arrive in Europe as well. In the Pacific war, US Army M10s were used for infantry support, but were unpopular due to their open-topped turrets, which made them more vulnerable than a fully enclosed tank to Japanese close-in infantry attacks.

Approximately 54 M10s were supplied to the Soviet Union, though their use by the Red Army is largely unrecorded. The M10 also equipped units of the Free French Army; one M10 named Sirocco, part of the Régiment Blindé de Fusiliers Marins composed of French sailors, famously disabled a Panther on the Place de la Concorde during the liberation of Paris. British M10s were designated as (Gun) 3 inch Self Propelled (3in SP) or "M10 3 in SP" and as with all British self-propelled guns were operated by Royal Artillery units. They saw action in Italy and France, many being upgunned with the more effective 17-pounder gun (as the 17pdr SP Achilles) from 1944 onwards.

The M10's open-topped turret theoretically left the crew vulnerable to artillery and mortar fire as well as infantry close assault, especially in urban combat and wooded areas, but this was not considered a major flaw in the US as American infantry carried significant support firepower when supporting the vehicles in the type of combat that made them most vulnerable. Moreover, the open-topped turret gave excellent visibility, which was valuable for a vehicle that was tasked with finding enemy armored vehicles and other targets. The open top also made escape easier when the vehicle was hit and improved communications with accompanying infantry. In action, some individual US crews improvised extra overhead armor in Normandy to protect against mortars and grenades. One M-10 was even photographed with an almost complete roof fitted to a raised edge which had vision slits, all manufactured out of captured German plating. In UK service, one M-10 in the 86th Anti-Tank Regiment (12th Corps) in Normandy drove back out of action three separate times with the entire turret crew dead. Two turret crews had been killed by the much feared 88mm air bursts or mortars exploding in treetops, one crew were killed by a direct hit through the turret. The same driver survived each time. When this driver was placed with a new crew, his fourth, he was declared to be a 'Jonah' (bad luck) and they refused to drive with him. He was transferred to another unit and told to keep quiet about his history.

By the end of the war its armor was clearly too thin to provide protection from the newer German tanks, anti-tank guns, and infantry anti-tank weaponry. M-10s in Europe were photographed with layers of sandbags or baulks of timber attached to front and side armor to detonate bazooka rockets and Panzerfausts before they struck the main plate. The M10 had a very slow turret rotation speed, as the turret traverse was unpowered and the crew had to hand-crank the turret around. It took approximately two minutes to rotate a full 360 degrees. However, this slow rotation speed may have been again more a theoretical flaw than real as compared to German armored fighting vehicles (AFVs), as the M-10 was generally more mobile than its turreted opponents in the most common tactical situations in Europe and had far better traverse than turretless German tank destroyers with virtually no traverse and which were much less mobile. The German Panzer IV Ausf. J, produced exclusively in 1944-45 also had manual-only turret traverse, which was still twice as fast as the M10, with the Tiger I having the same speed as the J's. Panthers and Tiger IIs could traverse four times as fast. The Sherman tank's traverse was the fastest of all, twice as fast as the Panther, and this was not considered a significant tactical advantage for the Sherman. What was more important was the fact that the US AFVs would generally operate in greater numbers in tactical situations and therefore had more firing angles and a greater rate of fire with accuracy than their German opponents, assuring that even in best case scenarios for the Germans in the West, they would lose more AFVs than they could afford. The Western European terrain permitted very little in the way of long distance ranges where the Germans could exploit their high velocity guns and heavy frontal armor. The lack of German AFV numbers is indicated by the fact that U.S. tank destroyers fired many more high-explosive shells than anti-tank ammunition, indicating that they were employed much like the tanks they were supposed to support. In UK service, the M-10 was normally issued to four-battery regiments of the Royal Artillery. Typically they were re-armed with the more powerful 17-pounder and, typically, two batteries had M-10s while two batteries had towed 17-pounders. One tactical theory was that the two towed batteries would form a gun line while an M-10 battery remained mobile on each flank and drove or led enemy tanks on to the static gun line. In practice, UK batteries were frequently separated in Normandy, with the M-10 batteries often being seconded to UK tank brigades. UK tank brigades were equipped with Churchill tanks which did not carry the 17-pounder gun.

In the final analysis, the M10, although it was clearly not a superior weapons system in Europe in 1944-45, proved to be useful, effective, and survivable enough to maintain unit strengths through replacement and repair.

The most decorated American soldier, Audie Murphy, earned his Medal of Honor at the Battle of the Colmar Pocket, when he used the heavy machine gun of an abandoned and burning M10 to repel German infantry. He was reportedly very disappointed when an M10 was not available for his reenactment of the event in the post-war film To Hell and Back and he had to use a Sherman in its place.

Ten German Panther tanks were modified to look like M10s in the Ardennes Offensive.

Variants

 * 3-inch Gun Motor Carriage T35 (Prototype): Early production Medium Tank M4A2 chassis.
 * 3-inch Gun Motor Carriage T35E1 / 3-inch Gun Motor Carriage M10 (3in SP, Wolverine in British service ): Diesel engine (~5000 vehicles)
 * 3-inch Gun Motor Carriage M10A1: M4A3 chassis, Ford GAA gasoline engine (~1700 vehicles)
 * 17pdr SP Achilles: M10 equipped with an Ordnance QF 17 pounder Mark V gun as used on the Sherman Firefly and British tanks. They can be identified by the muzzle brake at the end of the barrel and a counterweight behind the muzzle brake.
 * Diesel-engined M10 became 17pdr SP Achilles IC,
 * Gasoline-engined M10A1 became 17pdr SP Achilles IIC
 * Full-Track Prime Mover M35: Turretless M10A1 used as an artillery tractor
 * 3in SP Wolverine: Proposed Canadian-built version using a Ram tank chassis — a single prototype was built in 1942.
 * M10 Self-Propelled Howitzer (ROC): Previously-demilitarized M10 transferred to China and then in 1949 rearmed with modified ex-IJA 105mm infantry howitzers. Other modifications included a permanent turret roof with crew access/observation hatches, lighter but more impact-resistant armor plating, and a bow machine gun port. One prototype and 16 follow-on vehicles were made.

* SP = Self-Propelled