The M18 "Hellcat" served as the finest example of an American Army tank destroyer in World War 2. The type was fast, agile, well-armed and available in numbers sufficient to combat the armored forces of the German Wehrmacht across Europe. The M18 was an improvement over the preceding M10 series and proved as capable as the M36 "Slugger" family, managing its part for the ground successes needed in toppling Germany's late-war surges. The Hellcats served through to the end of the war and were even featured in the inventories of several nations in the post-war world.
The original M10 became the definitive American tank destroyer of World War 2 and was produced in nearly 7,000 examples for use by the US Army as well as the armies of its allies. However, the type was based upon the modified chassis of the M4 Sherman and lacked much in the way of armor protection. Its main gun was eventually shown to be largely inadequate as the war progressed. The M36 "Slugger" was then developed from the M10 family lineage to field a more potent 90mm main gun and this design was also based on the classic M4 Sherman tank chassis. It saw production reach 1,400 examples and was capable of tackling the latest German tank offerings but appeared towards the end of the war.
The design that was to become the M18 Hellcat was already in development as early as December of 1941. The Japanese attack on Pearl Harbor that month ushered the United States into total war with the Empire of Japan to which Germany and Italy declared war on the United States. British PM Churchill convinced US President Roosevelt that tackling Hitler and Mussolini in Europe and Africa was of priority so resources were geared towards such a foray.
A US Ordnance Department specification was issued for a "fast tank destroyer" design centered around the fitting of a 37mm main gun mount. The vehicle was to be powered by a Wright Continental R-975 C-series 9-cylinder radial engine with the suspension system based on the famed Christie arrangement. This made the new tank destroyer design the first American vehicle specifically developed for the tank-killing role as opposed to a design being a modification of an existing hull to fit the role.
By the middle of 1942, the T49 GMC ("Gun Motor Carriage") prototype emerged for review. By this time, actions in North Africa had already shown that the originally-intended 37mm armament was vastly inferior for the tank-killing role considering the armor quality of the latest German tanks. The prototype was given a 57mm caliber armament instead and was now fitted with a more universal torsion bar suspension system. Evaluations were ongoing and soon the need for ever-more potent armament became apparent for the German Army's reach had now gone beyond the point of fielding Panzer III and Panzer IV medium tanks - the excellent Panther and Tiger I heavy tanks were soon forming the backbone of all German Army actions and proving quite the fore. These German tanks sported highly-capable main guns with thick armor arrangements that outclassed all Allied tanks of the time. As such, the 75mm M3 main gun was selected for the future development in America's new tank destroyer.
The changes soon produced the "T67 GMC" pilot vehicle design which was a lighter, smaller vehicle the 75mm M3 main gun. The idea of fitting a 76.2mm main gun created the "T70 GMC" prototype model which became the preproduction design for what was to be designated the "M18 GMC". Serial production began in July of 1943 and spanned until October of 1944 to which 2,507 examples rolled out of American factories and into war. Operational status was achieved in the summer of 1944 and the M18 received the unofficial nickname of "Hellcat" in due time.
In the field, the M18 proved an excellent vehicle for the intended role. Her power-to-weight ratio provided the vehicle with an excellent top speed of 55 to 60 miles per hour in ideal conditions - faster than any other armored fighting vehicle of the war. The Continental powerplant allowed for great acceleration while the coupling of the engine with the chosen hull design made for a rather agile mount. It was the vehicle's speed that was often utilized as an inherent defensive measure where her armor protection could prove suspect, allowing M18 crews the capability to fire at an enemy and then retreat at speed before a response could be mustered. Her powertrain was noted as reliable and a major asset considering the unforgiving nature of war. The M18 was much smaller in profile and size while being half the weight of the M10 series before it. This made her a harder target to spot and engage. Her armor was improved over that of the M10 but still not entirely adequate when facing off squarely with enemy combat tanks - this job better left to the M4 Shermans and hidden anti-tank gun crews. German tankers actually enjoyed a major advantage when able to target the thinly-armored M18s. The gunnery crew still operated within an open-topped turret emplacement. While this exposed them to unnecessary battlefield dangers and the elements, it provided for unfettered views of the action and plenty of headroom for which to manage the functions of the main gun in the heat of battle. The 360-traverse of the turret also allowed the M18 the ability to engage targets in any direction without the need to turn the entire vehicle against a danger. In contrast, other tank destroyer contemporaries fielded in the war had their guns set within fixed superstructures - necessitating that the entire vehicle be pointed at the enemy. The M18 was nothing short of versatile, robust and effective throughout the war, in many ways making her the finest American tank destroyer of the conflict and a proven war-winner.
Combat actions involving the M18 found her battling across the European countryside and through its many villages en route to the German border. The new German Panther and Tiger I tanks showcased enviable armor protection and excellent gun arrangements but what they lacked was agility - itself a strongpoint of the M18. The M18 could maneuver and engage the weaker side and rear armor facings (through "flanking" maneuvers) typically before the German tanker crews could turn their turrets to counter. This helped M18 crews attain excellent initiative and limit their own losses in the field to a certain extent. The 76mm main gun on M18s was not entirely consistent but got the job done. The only German tank target the M18 crew could not match pound-for-pound was the heavier Tiger II series - but few Allied tanks could stand up to this beast and a lack of fuel and resources across wartime Germany was its biggest threat.
During July of 1944, the American 630th Tank Destroyer Battalion accounted for no less than 53 Panther medium and Tiger I heavy tanks in ensuing battles. The group also managed to net no fewer than 15 German self-propelled tracked vehicles during the same span. Of note among these totals was that only 17 Hellcats were lost to enemy action or other factors. It was this sort of kill-to-loss ratio that M18 crews enjoyed through the course of the war. The development of High Velocity Armor Piercing (HVAP) later in the war only served to make their 76.2mm guns more potent and increase penetration values against German targets.
Like the M10 before it, the M18 soldiered on in its tank destroyer battalions until it was rationalized that dedicated tank destroyer groups were no longer needed considering the advances made to combat tanks in general. Future armored warfare would rely strictly on tank-versus-tank battles that did not require the intervention of dedicated tank destroyers per se. As a result, American tank destroyers were fielded more and more as part of the direct armored force and not held in the reserve role, being called to action when needed. This placed such units more in line with the assault and self-propelled artillery roles in which they functioned alongside infantry actions and were further supported by air cover. The Allies enjoyed air superiority towards the end of the war which limited the reach of German assaults, especially on good weather days. The dedicated tank destroyer concept was effectively dead by war's end and dropped from American Army doctrine thereafter.
Such was the success of the M18 hull and powertrain that the US Army was quick to develop other useful battlefield roles for the type. A late-war development saw the fitting of a 150mm field howitzer to the M18 chassis to create the "T88 Howitzer Motor Carriage" prototype. This self-propelled artillery platform was undergoing testing when the war ended and subsequently saw no production beyond the prototype stage. The "90mm Cannon Motor Gun Carriage" attempted to fit a 90mm high-velocity main gun to the M18's turret but the end of the war stopped its progress. The "T41E1" prime mover and "M39" fast infantry carrier were also developed - each sans the turret of the original M18 - though the T41E1 fell to naught with the end of the war and the M39 (more formally as the "Armored Utility Vehicle M39") was produced in approximately 650 examples. Up to eight personnel could be carted in the M39 which was armed with 1 x 12.7mm Browning M2HB heavy machine gun for self-defense and these saw action in the upcoming Korean War. The "T65 Flame Tank" as well as the "T86", "T86E1" and "T87" amphibious howitzer vehicles all failed to make it to production. Other prototypes trialed included a mobile command post.
Design of the M18 was highly conventional and followed common American tracked vehicle practices of the time. The powerpack was settled in a compartment to the rear of the vehicle with the drive sprocket at the front of the hull. The track idler was set to the rear and four track return rollers managed the upper portion of the track systems themselves. There were five rubber-tired road wheels per track side with little in the way of side armor skirting for point defense against side direct hits. The turret was set just ahead of amidships and fitted the long barrel main gun, capped by a double-baffled muzzle brake (this found on M1A2 guns). The sides of the hull superstructure sported clean edges and were sloped inwards for ballistics protection. The open-topped turret was oblong from the overhead profile with an overhang at the rear for maximum internal stowage. The turret also featured sloped sides and an armored front facing for maximum protection within the required design weight limit. A close-in heavy machine gun was fitted to a flexible ring mount at the rear of the turret and could be operated by any of the turret crew.
The M18 was powered by a Continental R-975 C 9-cylinder radial, air-cooled, gasoline-fueled engine delivering 340 to 400 horsepower. This supplied the vehicle with a top speed of 55 miles per hour and an operational range of 150 miles. She held a crew of five including a driver, co-driver, a dedicated gunner, an ammunition handler and the tank commander. Primary armament was the 76mm (3 inch) M1A1 or M1A2 main gun with secondary armament - mostly for defensive purposes - supplied by a 12.7mm Browning heavy machine gun. The main gun was developed from the primary armament of the preceding M10 tank destroyer though improved. The M1A2 version main gun was identified by its muzzle brake which the M1A1 lacked. The machine gun was suitable for engaging (or suppressing) enemy infantry, light armored vehicles and low-flying attack aircraft. 45 x 76.2mm projectiles were carried aboard and these could be a mix of Armor-Piercing (AP) and High-Explosive (HE) ammunition types to counter just about any battlefield need. Armor protection was between 6mm and 25mm in thickness. The vehicle stood at 7 feet, 9 inches tall and weighed 16.76 tons.
Amazingly, the M18 Hellcat was still in operational service with the Yugoslavian Army in the early 1990s - either indicating the excellent design of the M18 Hellcat series or lack of modernization on the part of Yugoslavian authorities. These M18s saw combat by Serbia in the Yugoslav Wars that followed. Taiwan became another post-war user of the type as did the rebuilding "West" German Army. American Army M18s were in service from 1944 to 1957.
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