M18 Hellcat

The M18 Hellcat was an American tank destroyer of World War II. Armed with a 76 mm cannon, the vehicle was the fastest tracked, armored fighting vehicle during World War II with a top speed up to 60 mph (92kph), and Buick nicknamed it the Hellcat. The speed was attained by keeping armor to a minimum, no more than 1" thick. Hellcat crews took advantage of the vehicle's speed to minimize the enemy's ability to pierce its thin armor.

History
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 engine, and a 37 mm gun. 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. Even the Hellcat logo on the M18’s front corner and patches worn by its crew was designed by Earl’s staff. Flanked by the words “Seek, Strike, Destroy,” it depicts a wildcat biting down on crushed treads, signifying the Hellcat’s mission of targeting enemy tanks. Buick engineers brought the Hellcat to life from the design team’s sketches and developed an innovative torsion bar suspension that provided a steady ride. Though it weighed about 20 tons – the same as almost nine modern day Buick Enclaves – the Hellcat was designed to be one of fastest tanks on the battlefield and was capable of traveling upwards of 60 mph. Its power came from a nine-cylinder, 450-horsepower radial-type aircraft engine paired with a three-speed Hydramatic transmission. “The Hellcat was considered the hot rod of World War II,” said Bill Gross, a historian who restored an M18 now on display at the Sloan Museum in Flint, Mich. “To give perspective, most German tanks of the day were capable of just 20 mph and even today’s M1 Abrams tank is outpaced by the Hellcat.” Once developed, the Hellcat was tested in the same manner as millions of Buick 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. Of course, the M18 also required unique tests of its ability to ford six feet of water, climb small walls, and ram through structures. Production of the M18 Hellcat began in mid-1943 and ended in October 1944. The project was so secretive that a story about the “new” tank destroyer ran in newspapers just a month before production

During fighting in North Africa, the vehicle's original 37 mm gun was inadequate and the design was upgraded with a British 57 mm gun. During the development process, the design was further upgraded to a utilize a 75 mm gun, and then finally to the 76 mm gun. The Christie suspension requirement was also dropped, and replaced with a torsion bar suspension. The design was standardized in February 1943 and production began in July 1943.

Design
The M18's new design incorporated several innovative maintenance features. The Wright R-975 engine was mounted on 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 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, 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 armor, 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 nearly all fully tracked 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 frontal armor penetration, but this was never available in quantity.



Maneuver capability
While the M18 was capable of high road speeds this attribute was difficult to use successfully in combat, but along with the high top speed was a commensurate ability to accelerate rapidly and change direction rather quickly. Although sustained travel at road speeds was hardly ever used outside of the Allied response during the Battle of the Bulge, 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 a shot instead 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. 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.

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. M39s saw combat during the Korean War, primarily as armored personnel carriers and munitions carriers, and were finally declared obsolete on February 14, 1957. About 100 M39s were transferred to the West German Bundeswehr in 1956, where they were used to train the reestablished Panzergrenadier armored infantry units.

Production
The M18 continued in production until October 1944, when the war was nearing its end. 2,507 had been produced by that time, at a unit cost of $57,500. Though all tank destroyer units were disbanded by the U.S. after the war, surplus M18s continued to see limited service.

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

Use in the Pacific Theatre
When the Americans entered the war in 1941, they began to supply China with armored vehicles, including the M18 Hellcat. These, along with M3 Stuarts and M4 Shermans, trickled in through Burma and formed part of the several well-equipped, well-trained armies that the Chinese Nationalists deployed. These units were instrumental in stopping numerous Japanese attacks during the later phases of the war. However, due to the comparative rarity and poor quality of Japanese armor the M18 was often used in a fire support role instead of as a tank destroyer.

Use in Africa and 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. The tank destroyers were attached in platoon size units to American Infantry Divisions.

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 113 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.

The M18 Hellcat was a key element during World War II in the Battle of the Bulge. On December 19–20, the 1st Battalion of the 506th PIR was ordered to support Team Desobry, a battalion-sized tank-infantry task force of the 10th Armored Division (United States) assigned to defend Noville[3] located north-northeast of both Foy and of Bastogne just 4.36 miles (7 km) away. With just four 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 wherein the legendary top speed of the M18 Hellcat (55 miles per hour (89 km/h), faster than today's M1A2 Abrams) was actually used to get ahead of an enemy force.

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 1000 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.

Combat tactics
The Hellcat's 76mm gun often could not penetrate the thick sloped front armor of German Panther tanks. The Hellcat had very little armor, and the use of high flash powder made the Hellcat a highly visible and vulnerable target for German tank crews.

The Hellcat had a gun that could penetrate roughly 88mm of armor at 2000 m. This was enough to penetrate a Panzer IV (a tank originally designed in the 1930s) frontally, but not enough to deal with the newer Panther or Tiger from the front. The average combat range noted by the Americans for tank vs. tank action was around 800m to 900m. If facing a Panther, a Hellcat would be facing a tank with roughly 140mm of line-of-sight armor frontally that could not be pierced at any range, with a 100mm manlet that could be pierced at suicidally close range. However the 76mm 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 not exposing their vulnerable large side profiles.

Tank destroyer doctrine
American prewar armored doctrine was based on the assumption that enemy armored attacks would be delivered at a time and place of the enemy's choosing against an American defense. Similarly, American armored attacks would be delivered at a time and place of friendly forces choosing against an enemy defense. For this, the U.S. envisioned using tanks in the attack solely in a support and exploitation role, usually in conjunction with infantry. Tank destroyers, such as the Hellcat, 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 aid these purposes, it was designed with light armor and extremely high speeds. U.S. doctrine originally called for the Hellcat to be held in reserves so that it could block an incoming armored thrust.

This doctrine failed on the 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, taking on the role of self-propelled anti-tank guns. During the battle for Italy, tank destroyers compensated for a shortage of 155mm artillery ammunition by using their 3 inch or 76mm 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 practice a tank destroyer battalion was assigned nearly permanently to a division and would move toward an enemy penetration from local assembly areas. The doctrine of the time had Shermans acting in support of infantry to break enemy defenses (Infantry leads, tanks follow or support by fire), and then exploiting the attack (Tanks lead, infantry follows) with infantry in support during exploitation.

Prewar expectation was that all anti-tank work was supposed to be done by tank-destroyer crews, because attacking tanks could concentrate against a small part of a defending line. Independent tank destroyer groups were to counter concentrate, to stop enemy tanks from penetrating deeply. Speed was essential in order to bring the Hellcats from the rear to destroy incoming tanks. Obviously this would make it harder for an armored force to achieve a deep breakthrough, a main objective of armor, if the enemy had tanks. It would also be easier for an opposing armored force to achieve a local breakthrough against an American unit which would not have all of its anti-tank assets at the front during the beginning of any attack. This doctrine was not entirely used as it would create a small window of time of weakness in the armored battalion until tank destroyers moved to the front. Tank destroyer battalions assigned to front line divisions often split up to companies attached to regiments, and platoons attached to infantry battalions. When so attached, defending tank destroyer units supplemented organic antitank weapons (bazookas and 57mm towed guns).

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).

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.

Prototype variants

 * 105 mm Howitzer Motor Carriage T88: M18 with the 76 mm gun replaced with a 105 mm T12 howitzer; 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 specially designed flotation hull, using its tracks for water propulsion.
 * 76 mm Gun Motor Carriage T86E1 (Amphibious): Same as T86, but with the addition of propellers for propulsion.
 * 105 mm Howitzer Motor Carriage T87 (Amphibious): This model had the 105 mm T12 howitzer of the T88, and like the T86, used its tracks for water propulsion.

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