The M18 76mm Gun Motor Carriage 'Hellcat' was the most successful American tank destroyer of the Second World War, using its mobility to compensate for its thin armour and accounting for a large number of German tanks during the fighting in 1944-45.
The M18 underwent a lengthy development process, with several changes of design to counter changes on the battlefield. It began life as the T42 37mm Gun Motor Carriage, a General Motors design for a vehicle with a lower profile than the Sherman tank-based M10 GMC. Work on the T42 began in response to General Staff memo of 2 December 1941 that called for a vehicle using Christie suspension, with a 37mm mm. It was to be powered by a Wright Continental engine.
On 1 April 1942 the army decided to move from the 37mm gun to the 57mm gun. The T42 became the T49 57mm Gun Motor Carriage. On 18 April 1942 two pilot vehicles were ordered. One was completed with the 57mm gun, but Army Ground Forces then decided not to the 37mm and 57mm guns in future tank destroyers.
In July 1942 General Bruce, commander of the Tank Destroyer centre, asked General Motors if they could produce an upgunned version of the T49. They responded with the T67, which was armed with a 75mm M3 gun (as used in the Sherman tank), had Christie suspension and was powered by two Buick engines. The second pilot T49 was completed as the single T67 and underwent tests at the Aberdeen Proving Ground toward the end of 1942.
The final development version was the T70 76mm Gun Motor Carriage. Tank Destroyer Command asked for the 75mm gun of the T67 to be replaced with the new M1 76mm gun. This had been developed in an attempt to produce a lighter version of the standard 3in anti-tank gun, suitable for use in medium tanks. It was used in the Hellcat and in later versions of the M4 Sherman. The new gun was carried in an open turret, with no turret basket.
The 3in gun weighed 1,990lb and had a total length of 158.1in. The new 76mm M1 weighed only 1,141lb despite being slightly longer, at 163.75in. The two guns used similar ammunition, with the same projectiles but different powder cartridges. A complete APC M62 round for the 3in gun weighed 27.24lb; the equivalent round for the 76mm gun was only 20.77lb. Despite the lighter cartridges the two guns had the same muzzle velocity and armour penetration.
Earlier designs in the series had used Christie suspension, but the T70 used torsion bar suspension. It was powered by a Wright Continental R975-C1 engine, with the drive wheel at the front (the earlier prototypes had the drive wheel at the back).
Six pilot models were ordered from General Motors in January 1943, although this stage the army was confident in the basic design, and placed a production order for 1,000 T70s, armed with the M1A2 76mm gun, on 7 January 1943.
The six pilot vehicles were delivered in July 1943. Trials with the pilots suggested that a few changes were needed, including a simplified hull front and a modified turret with a bustle that acted as a counterweight and provided storage.
Full production at Buick began in August 1943, when 83 vehicles were delivered. The Buick publicity department gave the vehicle the name 'Hellcat', and it was widely but unofficially known by this name. The T70 was finally standardized as the M18 76mm Gun Motor Carriage in February 1944 by which time 1,056 had already been completed and the peak of production had already passed, with 267 being completed in November 1943 and 250 In January 1944. A total of 2,507 M18s (including the 6 pilots) were built, and production ended in October 1944.
Production then switched to the T41/ M39 Armoured Utility Vehicle, which used the same chassis but with the turret removed. 640 (or 700) of these vehicles were produced between October 1944 and March 1945, and they were used as a prime mover and s a reconnaissance vehicle. 640 of these vehicles were produced from some of the first 685 Hellcats, which had to be returned to factory to have the gears modified.
There was some concern that the M18 would be mistaken for a German vehicle because of the torsion bar suspension, which was rare on American vehicles but used on several German tanks. In an attempt to avoid this, the new vehicle was taken on a tour of American units, and often had over-sized national markings.
The M18 had five road wheels on each side, with four return wheels. It had a raised idler at the rear and sprocket drive wheel at the front. The track was 14.38in wide. In early vehicles both the idler and drive wheel could be adjusted to alter track tension, but later on only the drive wheel could be adjusted.
The turret was round, with sloped sides and a bustle at the rear that acted as a counterweight and provided storage space. The turret was open topped, with a ring mount for an anti-aircraft machine gun at the left-rear.
The superstructure had a level top, with a raised area behind the turret (over the engine). The sides were slightly sloped. The nose was in two parts, with the lower part (level with the tracks) sloped at 45 degrees and the upper part more steeply sloped back, although there was still a large area of flat deck in front of the turret.
The M18 was armed with several different versions of the 76mm gun. The M1A1 was the basic model with no muzzle brake. The M1A1C and M1A2 could both take a muzzle brake. The M1A1C had right-hand rifling with one full turn in 40 calibre lengths, the M1A2 was rifled with one full turn in 32 calibres. The gun could fire armour piercing, high explosive, illuminating and smoke shells. In the tank destroyer role it normally carried 75% AP and 25% HE shells, but the vehicle was often used in the fire support role with extra shells provided.
The tank destroyer doctrine meant that the M18 had some design flaws. The idea was that the tank destroyers would be used to attack and defeat any German armoured breakthroughs, and so would be operating behind Allied lines and well away from German infantry. When the M18 entered combat it was soon clear that this would rarely if ever be the case. By 1944 the Germans weren't making many massed armoured attacks, and when they made smaller scale attacks their tanks were nearly always supported by infantry. This meant that the open top to the turret made the M18's crew vulnerable to grenades and small arms fire. A second problem was that the only machine gun carried by the M18 was the anti-aircraft gun on the turret roof. Anyone operating this machine gun was totally exposed to enemy small arms fire.
The biggest strength of the M18 was its speed, which was twice that of the M10 or M36 tank destroyers and significantly above that of the M24 Chaffee Light Tank. This meant that the M18 was able to use 'hit and run' tactics to inflict heavy damage on significantly more powerful German armoured vehicles, without suffering overly heavy losses.
T86 and T86E1 76mm Gun Motor Carriage (Amphibious)
The T86 and T86E1 were developed in 1944 in an attempt to produce an amphibious version of the M18. A new amphibious hull with a flat fronted bow was developed. The T86 and T86E1 were tested in the spring of 1944 and work then moved onto the T87.
T87 105mm Howitzer Motor Carriage (Amphibious)
The T87 followed on from the T86. It had a modified hull and carried a 105mm howitzer in an open turret. It was ready for trials by December 1944 but the project was cancelled at the end of the war.
T88 105mm Howitzer Motor Carriage
The T88 was a more straightforward conversion that mounted a 105mm howitzer in a standard land-based M18. Two different turrets were developed, but the project was cancelled at the end of the war.
One M18 was modified in June 1945 by giving it the turret from the M36 90mm Gun Motor Carriage. Wider 21in tracks were installed to cope with the extra weight of the 90mm gun and its shells and the internal storage spaces were modified to make space for the bigger shells. The 'Super Hellcat' was a technical success, but it was cancelled at the end of the Second World War.
The Hellcat made its combat debut as the T70 in May 1944 when two of the pilot vehicles took part in the Anzio landings. They performed well in this early battle, and were seen as a great improvement on the M10.
Production M18s began to reach Italy in September 1944, reaching the 805th Tank Destroyer Battalion in the same month. They remained in use in Italy to the end of the war, taking part in the final battles in the Po valley in the spring of 1945.
The M18 began to appear in significant numbers after D-Day. A total of 689 were in the field by 15 August 1944, and its first major test came during the siege of Brest. The urban environment didn’t suit the M18, which relied on its mobility for protection, but it played a useful role in the battle, which lasted until 19 September.
The 603rd and 704th Tank Destroyer Battalions began to use the M18 in combat late in July, taking part in Operation Cobra, the breakout from Normandy.
A significant number of M18s were involved in one of the few really sizable tank battles of the French campaign, a clash between American and German tanks at Arracourt on 19 September 1944. The M18 now began to demonstrate its strengths, using it mobility and speed to take advantage of the terrain around Arracourt. The M18 battalions became involved in a close-range battle with a force of Panthers and Panzer IVs, and inflicted heavy losses on the Germans.
The 602nd, 609th and 705th Tank Destroyer Battalions entered combat with the M18 in October 1944. The 811th followed in November, the 638th and 817th in December, the 643rd in January 1945, the 656th, 661st and 809th in February 1945
The 827th Tank Destroyer Battalion (Colored) converted from towed AT guns to the M18 in July 1944. It was deployed in November and fought in Alsace, but was withdrawn in February 1945.
The M18 saw action during the Battle of the Bulge. This was the only major German panzer offensive of the campaign in north-western Europe, and so the only time when the tank destroyers were used in their original role. Even then they were rarely able to act in large numbers against large groups of German tanks, but instead were used in individual defensive positions. One example was the 705th Tank Destroyer Battalion, which was trapped within Bastogne. The M18 performed acceptably during this battle, but the 76mm gun wasn't quite powerful enough and the lack of armour protection still caused a problem. The M36 90mm GMC was considered to have been more successful, but still suffered from weak armour.
After the Battle of the Bulge the 612th Tank Destroyer Battalion converted to the M18, where it had lost many of its towed anti-tank guns.
The 801st Tank Destroyer Battalion was partly equipped with the M18 in March 1945. The 820th and 824th converted from towed anti-tank guns to the M18 in the same month, as did the 822nd in April.
The 633rd Tank Destroyer Battalion got the M18 in May 1945 and used it for the last few days of the war. The 807th began to convert to the M18 too late to complete the process.
The M18 was used in the south of France in the aftermath of Operation Dragoon.
The first unit to receive the M18 in the Pacific was the 637th Tank Destroyer Battalion, which had received its first vehicles by August 1944. As with the earlier tank destroyers the open turret of the M18 made it vulnerable to Japanese infantry attacks, but again as with earlier tank destroyers the more powerful gun was welcome.
The M18 made its combat debut during the invasion of the Philippines. It was also used during the invasion of Okinawa, the final land battle of the Second World War.
After the war the US army studied the combat record of 39 tank destroyer battalions. Between them they claimed 1,344 German tanks and assault guns (34 per battalion), and an average of 17 pillboxes, 16 machine gun nests and 24 other vehicles. The US Army decided that the tank destroyer battalions had been less effective than an equivalent number of normal tank battalions, and the tank destroyer battalions were all disbanded after the war.
A number of M18s were given to the Yugoslav People's Army the 1950s. They were still usable in the early 1990s and some served with the Serbian forces in Bosnia during the Yugoslav civil war.
Hull Length: 21ft 10in
Hull Width: 9ft 9in
Height: 8ft 5in
Crew: 5 (commander, driver, three gunners)
Weight: 40,000lb battle weight, 35,526lb empty
Engine: 340hp Continental R975-C1 (first 1,349 vehicles) then 400hp R975-C4
Max Speed: 55mph road speed, 20mph cross country
Max Range: 105-150 miles road radius
Armament: M1A1, M1A1C or M1A2 76mm L/55 gun with 45 shells, plus one flexibly mounted anti-aircraft machine gun
Turret front: 1in / 25mm
Turret sides and rear: 0.5in/ 13mm
Hull front, sides and rear: 0.5in/ 13mm
Hull top: 5/16in/ 8mm
Floor: 0.25in/ 6mm