M18 Hellcat

76 mm Gun Motor Carriage M18
Type	Tank destroyer
Place of origin	United States
Production history
Designed	1942
Manufacturer	Buick division of General Motors
Unit cost	$55,230[1]
Produced	July 1943 – October 1944
Number built	2,507
Specifications ([2])
Weight	39,000 lb (17.7 metric tons)
Length	17 ft 4 in (5.28 m) hull 21 ft 10 in (6.6 m) including gun
Width	9 ft 5 in (2.87 m)
Height	8 ft 5 in (2.57 m) over antiaircraft machine gun
Crew	5 (Commander, gunner, loader, driver, assistant driver)
Armor	0.19 to 1.0 in (4.8 to 25 mm)
Main armament	76 mm gun M1 or M1A2 45 rounds
Secondary armament	.50 caliber (12.7 mm) Browning M2HB machine gun 800 rounds
Engine	Continental R-975-C1 or C4; 400 hp (298 kW) at 2,400 rpm
Power/weight	22.6 hp/metric ton
Transmission	900T Torqmatic 3 speeds forward, 1 reverse
Suspension	Torsion bar
Fuel capacity	165 US gallons (625 litres)
Operational range	100 mi (160 km)
Speed	50 mph (80 km/h)

The M18 Hellcat (officially designated the 76 mm Gun Motor Carriage M18 or M18 GMC for short) was an American tank destroyer of World War II, used in the Italian, European, and Pacific theatres, and in the Korean War. It was the fastest American tracked armored vehicle until the turboshaft-powered M1 Abrams main battle tank appeared decades later.^[3] Even then, most sources list the M1 Abrams with a top speed of only 45 mph (governed speed), leaving the Hellcat with a superior paved-road top operating speed. The speed was attained by keeping armor to a minimum, no more than one inch thick and roofless, open-top turrets (a standard design feature for all American fully tracked tank destroyers of World War II) and by powering the relatively small vehicle with a radial engine originally designed for aircraft usage. The Hellcat, along with the M4 Sherman-based M10 tank destroyer and the highly effective, 90mm gun-armed M36 tank destroyer, provided American and Allied forces with a respectable mobile anti-tank capability against the newer German armored types. Despite being armed with an only partially effective 76 mm cannon,^[4] it performed well.

The Hellcat was the most effective American tank destroyer during World War II. It has a higher kill to loss ratio than any tank or tank destroyer fielded by American forces in World War II.^[5][6]

Development

When the Tank Destroyer Force was organized in 1941, their commander Lieutenant Colonel (later General) Andrew Davis Bruce envisioned the units being equipped with something faster than a tank, with a better gun but less armor to allow for speed, a cruiser rather than a battleship.^[7] He objected to the 3 inch M10 Gun Motor Carriage because it was too heavy and slow for his needs,^[8] and later on to the 90 mm M36 Gun Motor Carriage because it was essentially an M10 with a bigger gun.^[9] The United States Ordnance Corps made several failed attempts to provide said vehicle using the weapons (the 37 mm, 57 mm, 3 inch, 75 mm and finally the lightweight 76 mm of 1942–1943) and technology available, including mounting the 3-inch gun on the fast M3 Light Tank chassis.^[10] The M18 was the end product of a long line of research vehicles aimed at providing the desired machine.

In December 1941, the Ordnance Corps issued a requirement for the design of a fast tank destroyer using a Christie suspension, the Wright-Continental R-975 radial engine, and a 37 mm gun. Two pilot vehicles were to be built.^[11]

The M18 originated in the design studio of Harley Earl from the Buick motor company division of General Motors, whose team also worked extensively on early camouflage paint.

Buick engineers used a torsion bar suspension that provided a steady ride.^{[lower-alpha 1]} Though it weighed about 20 tons, the Hellcat was capable of traveling upwards of 60 mph. Its power came from Wright R-975, a nine-cylinder, 450-horsepower radial-type aircraft engine, paired with a three-speed 900T Torqmatic transmission.

Changes to the specification mean that the first pilot – the 57 mm Gun Motor Carriage T49 – was built with the British (57 mm) QF 6-pounder gun instead of the 37 mm and a torsion bar suspension instead of the Christie suspension. It was tested in 1942 but the army wanted a heavier gun – the same 75 mm gun M3 as used on the M4 Sherman medium tank. The T49 project was cancelled and the second pilot was built with the 75 mm gun as the 75 mm Gun Motor Carriage T67. This met approval but in early 1943 the army requested a more powerful gun – the 76 mm gun M1 under development for the Sherman. Six pilot models – as the 76 mm Gun Motor Carriage T70 – were built with this gun. The trials of these models led to a new turret and changes to the hull front but, the design was otherwise accepted for production which began in July 1943.^[11]

Once developed, the Hellcat was tested in the same manner as passenger cars before and after it, at the General Motors Milford Proving Ground. Top speed testing was done on a paved, banked oval and ride quality tests were done over specially developed stretches of bumps. The M18 also required additional tests of its ability to ford six feet of water, climb small walls, and ram through structures.

The first models of the tank destroyer were tested by the US Army's 704th Tank Destroyer Battalion. The unit had originally been trained on the M3 Gun Motor Carriage (a 75 mm gun installed in the bed of an M3 half-track). Despite its T70 prototypes requiring several improvements, the 704th had "superlative" testing record, and the unit was later issued production Hellcats after many of their suggestions were integrated into the vehicle. The testing phase of the Hellcat proved that teamwork was an essential element of the new light tank destroyer units, and replaced the fixed, rigid structure of other units with a much more flexible command structure that allowed adapting to more complicated tasks.^[12]

Design

The M18's new design incorporated several labor saving and innovative maintenance features. The Wright R-975 engine was fully unitized, as it was mounted on rails equipped with steel rollers that allowed maintenance crews to disconnect it easily from the transmission, roll it out onto the lowered engine rear cover, service it, and then reconnect it to the transmission. The transmission could also easily be removed and rolled out onto a front deck plate to facilitate quick inspection and repairs.

In contrast to the M10 tank destroyer, which used the heavy chassis of the M4 Sherman, the M18 Hellcat was designed from the start to be a fast tank destroyer. As a result, it was smaller, lighter, more comfortable, and significantly faster, but carried the same gun as the Sherman 76 mm models. The M18 carried a five-man crew as well as 45 rounds of main gun ammunition, and an M2 Browning machine gun on a flexible ring mount for use against aircraft and infantry.

The main disadvantages of the M18 were its very light open-topped armor protection, and the inconsistent performance of its 76 mm gun against the frontal armor of later German designs such as the Tiger and Panther. The open-topped turret—a characteristic which it shared with all American tank destroyers—left the crew exposed to snipers, grenades, and shell fragments. The doctrinal priority of high speed at the cost of armor protection thus led to a relatively unbalanced design. The problem of the main gun performance was remedied with High Velocity Armor Piercing (HVAP) ammunition late in the war, which allowed the 76 mm gun to achieve greater armor penetration, but this was never available in quantity.^[13] The 76 mm gun with standard ammunition could only penetrate the frontal turret armor of Panther tanks at very close ranges,^[14] whereas the HVAP ammunition gave it a possibility of effectively engaging some of the heavier German tanks and allowing to penetrate the Panther turret at ranges of about 1,000 m (1,100 yd).^[4][15]

Production

Original plans called for a total of 8,986 M18s to be supplied – 1,600 for Lend Lease to other countries and 7,386 for the US Army. Production plans of the M18 were curtailed to 2,507, not including the six pilot models, of which 650 were converted to M39 armored utility vehicles, leaving 1,857 combat vehicles. The reasoning behind the reduction (in no particular order) was that:

• The Army Ground Forces preferred the 90 mm Gun Motor Carriage M36 for firepower and overrode Tank Destroyer Force commander Andrew Bruce's objections to adopting it
• The number of self-propelled Tank Destroyer battalions had been reduced to about half due to a policy change forced by the AGF who wanted towed guns to be used and hence far fewer self-propelled units were needed for the Tank Destroyers
• There was little potential Lend Lease activity: Britain and Soviet Union did not care for it.^[16] Two were transferred to the United Kingdom, and five to the Soviet Union.^[17]

Production of M18 Hellcats ran from July 1943 until October 1944, with 2,507 built. Several changes were made during production. The 76 mm gun M1 fitted to most Hellcats kicked up large amounts of dust when it fired. This was enough to impede the vision of the crew, who had to wait until the muzzle blast cleared to fire accurately again. To solve this problem, the 76 mm gun M1 was replaced with the muzzle brake-equipped 76 mm gun M1A2 as soon as it became available. Beginning in June 1944, the last 700 Hellcats received this new gun. Hellcats with serial numbers 1350 and below had the naturally-aspirated R-975 C1 engine. The ventilation grate for the transmission and oil coolers behind the driver's hatch on these early Hellcats had a bulged shape, protruding above the line of the upper hull. M18s with serial numbers 1351 and above had the supercharged R-975 C4 engine. At roughly the same time as the change in engine type, the shape of the ventilation grate was changed to be flush with the upper hull.^[18]

There were three production contracts for the Hellcat: RAD-563 covered the six pilot models. T-6641 was for the first 1,000 vehicles, and T-9167 was for the final 1,507 vehicles.^[19][20]

M18 Hellcat of the 824th Tank Destroyer Battalion in action at Wiesloch, Germany, April 1945.

Combat performance

The M18 served primarily in Western Europe, but was also present in the Pacific.

Use in the Pacific Theatre

M18s served in tank destroyer battalions supporting US Army infantry divisions in the latter stages of the war, notably in the Phillipines and Okinawa. M18s were not issued to Marine Corps units.

Use in Europe

The T70 prototype for the M18 first saw combat at Anzio, Italy, and production versions of the M18 were used in North-West Europe and Italy from the summer of 1944 onwards. Typically, every US Infantry or Armored Division had a Tank Destroyer Battalion attached on a long-term basis.

Notable battles

On September 19, 1944, in the Nancy bridgehead near Arracourt, France, the 704th Tank Destroyer Battalion was attached to the 4th Armored Division. Lt. Edwin Leiper led one M18 platoon of C Company to Rechicourt-la-Petite, on the way to Moncourt. He saw a German tank gun muzzle appearing out of the fog 30 feet away, and deployed his platoon. In a five-minute period, five German tanks of the 113th Panzer Brigade were knocked out for the loss of one M18. The platoon continued to fire and destroyed ten more German tanks while losing another two M18s. One of the platoon's M18s commanded by Sgt Henry R. Hartman knocked out six of the German tanks, most of which were the much-feared Panthers.^[23]

The M18 Hellcat was a key element during World War II in the Battle of the Bulge.^[24] On December 19–20, the 1st Battalion of the 506th Parachute Infantry Regiment was ordered to support Team Desobry, a battalion-sized tank-infantry task force of the 10th Armored Division assigned to defend Noville located north-northeast of both Foy and of Bastogne just 4.36 miles (7 km) away. With just four^[25] M18 tank destroyers of the 705th Tank Destroyer Battalion to assist, the paratroopers attacked units of the 2nd Panzer Division, whose mission was to proceed by secondary roads via Monaville (just northwest of Bastogne) to seize a key highway and capture, among other objectives, fuel dumps—for the lack of which the overall German counter-offensive faltered and failed. Worried about the threat to its left flank in Bastogne, it organized a major joint arms attack to seize Noville. Team Desobry's high speed highway journey to reach the blocking position is one of the few documented cases^[25] wherein the top speed of the M18 Hellcat – 55 miles per hour (89 km/h) – was actually used to get ahead of an enemy force.^[25]

An M39 carrier used in the Korean War.

The attack of 1st Battalion and the M18 Hellcat tank destroyers of the 705th TD Battalion near Noville together destroyed at least 30 German tanks and inflicted 500 to 1,000 casualties on the attacking forces, in what amounted to a spoiling attack. A Military Channel historian credited the M18 destroyers with 24 kills, including several Tiger tanks, and believes that in part, their ability to "shoot and scoot" at high speed and then reappear elsewhere on the battlefield, confused and slowed the German attack, which finally stalled, leaving the Americans in control of the town overnight.^[25] However, actual German combat records show that no Tiger tanks were in operation in the area at the time and that the nearest Tigers were some 20km to the south east, still in Luxembourg.

Combat tactics

The average combat range noted by the Americans for tank vs. tank action was around 800 to 900 m (2,600 to 3,000 ft). The Hellcat had a gun that could penetrate roughly 3.5 in (88 mm) of armor at 2,000 m (2,200 yd), which was enough to penetrate a Panzer IV medium tank frontally. However, against the Panther, a Hellcat would be facing a tank with roughly 5.5 in (140 mm) of line-of-sight armor frontally that could not be pierced at any range, with a 3.9 in (100 mm) mantlet that could be pierced only at extremely short ranges unless using the exceedingly rare HVAP ammunition.^[13][14] The 76 mm gun could knock out the Panther with relative ease from the flanks and rear, as the turret and side armor was weak and the quality of German armor plate declined in the last two years of the war. While Panthers in defense were formidable, Panthers in the attack had great difficulty with not exposing their vulnerable large side profiles. A common tactic for any AFV is employing the use of Hull down firing positions. This allows the vehicle to remain mostly behind cover while engaging the enemy.

Tank destroyer doctrine

American prewar armored doctrine was based on the assumption that massed enemy armored attacks would be delivered at a time and place of the enemy's choosing against an American defense. U.S. doctrine therefore originally called for the tank destroyer units to be held in reserve so that they could quickly deploy to destroy such massed armored thrusts. These independent tank destroyer groups were to quickly concentrate, to stop enemy tanks from penetrating deeply.

Similarly, US armored attacks would be delivered at a time and place of friendly forces choosing against an enemy defense. For this, the US envisioned using tanks in the attack in a support and exploitation role, usually in conjunction with infantry. Tank destroyers were to be used against tanks that had already penetrated the front lines. The Hellcat was not intended to engage in protracted combat but to quickly respond to breakthroughs in the line by enemy armor. To accomplish this, it was designed for very high mobility at the expense of armor protection.

This doctrine failed on the European battlefield where attacking Sherman tanks ran into defending German tanks far more often than intended and the tank destroyers were called in to assist. Tank destroyers were often deployed to attack enemy armor at long range from an ambush position. During the battle for Italy, tank destroyers compensated for a shortage of 155mm artillery ammunition by using their 3 inch or 76 mm guns in indirect fire role. Near the end of the war, there were so few German tanks that tank destroyers were increasingly used as self-propelled artillery in support of infantry for lack of any other targets. In effect, they were used exactly like tanks.

In practice, tank destroyer battalions were not held in reserve but were attached nearly permanently to divisions. Tank destroyer battalions assigned to divisions were often split up, with TD companies attached to infantry regiments, or platoons attached to infantry battalions. When so attached, defending tank destroyer units supplemented organic antitank weapons (bazookas and 57mm towed guns).^[26]

Mobility

While the M18 was capable of high road speeds, this attribute was difficult to use successfully in combat.^[25]

Although sustained travel at road speeds was hardly ever used outside of the Allied response during the Battle of the Bulge,^[25] most Hellcat crews found the higher speeds especially useful in a sprint to flank German tanks, which had relatively slow turret traverse speeds, and such maneuvering allowed the tank destroyer crew to direct a shot into the enemy's thinner side or rear armor.

In general, Hellcat crews were complimentary of their vehicle's performance and capabilities, but did complain that the open top created a cold interior in the Northern European winter of 1944–45.^[25] This problem was not helped by the fact that the air-cooled engine pulled a percentage of its cooling air through the crew compartment, creating in effect, a large armor-plated refrigerator. It was not designed to do so, but it proved impossible to seal off the crew compartment entirely from engine induced drafts.

Post war

After World War II, many M18s were sold to other countries. These were rebuilt and refurbished by Brown & Root in northern Italy in the late 1940s and early 1950s, and bear data plates that indicate those rebuilds. One of the users was Yugoslavia, which kept them in reserve until the early 1990s. A number of these vehicles were later used by the Military of Serbian Krajina and Army of Republika Srpska during the Yugoslav wars. One example was used on an armored train named the "Krajina express" (Krajina Ekspres).^[27]

The Military of the Republic of China also operated several M18s until their chassis and hulls were worn out, at which point the turrets were salvaged and installed onto surplus hulls of M42 Duster anti-aircraft vehicles to produce Type 64 light tanks.

The Venezuelan military still operates M18s, with 75 still in reserve service. An unknown number of these vehicles were modernized by a Yugoslavian firm in 1991.

An M18 is on display at the Army Heritage and Education Center in Carlisle, PA. M18 Hellcat "Amaz N Grace" is on loan to the Museum of American Armor in Old Bethpage NY, from the US Military Museum.

Armored Utility Vehicle M39 in Korea, 1952.

Variants

The only M18 variant which was produced in significant numbers was the M39 Armored Utility Vehicle, a turretless variation used to transport personnel or cargo or as a gun tractor. This version was armed with a single M2 machine gun on a flexible mount. 650 early production M18s were converted into M39s by removing the turret and fitting seats for up to eight men in the open fighting space.^[28] M39s saw combat during the Korean War, primarily as armored personnel carriers and munitions carriers, and were finally declared obsolete on February 14, 1957.^[29] About 100 M39s were transferred to the West German Bundeswehr in 1956, where they were used to train the reestablished Panzergrenadier armored infantry units.^[30]

Variants

• 105 mm Howitzer Motor Carriage T88

M18 with the 76 mm gun replaced with a 105 mm T12 howitzer. A pilot was built in 1944 but project cancelled after the end of the war.

• 90 mm Cannon Motor Gun Carriage: M18 with the 76 mm gun replaced with a 90 mm Cannon; cancelled after the end of the war
• 76 mm Gun Motor Carriage T86 (Amphibious)

M18 with a much larger and lightweight flotation hull, using its tracks for water propulsion. The T86E1 variant test vehicle used propellers for propulsion.

• 105 mm Howitzer Motor Carriage T87 (Amphibious)

The T86 vehicles had shown that track propulsion was better and this was used for the T87 which had the same 105 mm T12 howitzer of the T88.

All work on the three amphibious models was canceled after the end of the war.

See also

• G-numbers
• M36 tank destroyer, the heaviest-gunned (90 mm) US tank destroyer of World War II.

Notes

References

External links

Wikimedia Commons has media related to M18 Hellcat.

• 76mm Gun Motor Carriage M18 (with photos) – AFV Database
• Armored Utility Vehicle M39 – AFV Database
• M18 Tank Destroyer, Hellcat – World War II Vehicles (photos and video)
• "WWII tank to join in parade" – Daily Herald (Utah), 3 July 2008
• M18Hellcat.com, a website dedicated to the history and preservation of the M18 Hellcat
• Tankdestroyer.net (Web based United States tank destroyer forces information resource)