M18 Hellcat - History

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.

In light of experience gained in North Africa, the 37 mm gun was found to be inadequate and the design was changed to use a British 57 mm gun. During the development process, the design was further upgunned to 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.

As a new design, the M18 incorporated several innovative maintenance features. The Wright R-975 engine was mounted on steel rollers, which permitted it to be disconnected from the transmission, rolled out onto the lowered engine rear cover, serviced and then reconnected to the vehicle. Similarly, the transmission could be removed and rolled out onto a front deck plate to allow inspection and repairs.

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.

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 the M10) 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 an 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.

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 armour plated refrigerator. It was not designed to do so, but it proved impossible to seal off the crew compartment entirely from engine induced drafts.

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.

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.