The M18 was designed from the start to be a tank destroyer and it became the fastest fully tracked vehicle used in World War II.
On December 2, 1941, a memorandum from the G-3 to the G-4 of the General Staff recommended that a gun motor carriage be developed to carry a 37 mm M6 gun on a Christie type suspension. On April 1, 1942, the Ordnance Department suggested that a 57 mm M1 gun be used.
The M18 Hellcat was to rely on its maneuverability to help defend against enemy vehicles.
The driver sat on the left and the assistant driver on the right. Located between them was the transmission with the shift levers on top. This allowed for either to shift the gears. Each had an accelerator pedal with the assistant driver having a lockout mechanism. Each had steering levers that would hang down, and the levers could be moved out of the way. On the left side of the driver was the instrument panel. There were adjustable seats for both. In the roof each had hinged double doors. These also had periscopes.
The turret basket contained three folding and adjustable seats in an open turret. The commander was on the left side behind the gunner. The loader was located on the right side of the 76 mm gun.
The gunner could use either a hydraulic or hand traverse control to rotate the turret. He also had an azimuth control. Periscopic and telescopic sights were used by the gunner.
There was an auxiliary generator, located in the sub floor at the right front of the turret, that was used to recharge the batteries.
The assistant driver had a portable fire extinguisher beside him.
The turret bulge held the radio equipment.
The fuel tanks were located on each side of the engine. The left held 75 gallons and the right 90 gallons.
A propeller shaft went under the sub floor transmitted power from the engine to the transmission.
The torqmatic transmission was mounted on extension rails so it could be slid out for repairs.
There were controls inside and outside of the engine compartment that controlled its fire extinguisher.
Starting with vehicle 1,700 it had blowers that would move hot air over the oil cooler, the battery, the engine, and to the crew. This equipment was sometimes installed at tank depots for earlier vehicles to winterize them.
The M18 was armed with the 76 mm M1A1, M1A1C or M1A2 L/55 gun.
The M1 could fire 16,100 yards / 14,721 m with APCBC/HE-T ammunition.
The M1A1 had no muzzle brake. The M1A1C has threads for a muzzle brake and the barrel had rifling of one turn for each 40 calibers. M1A2 had threads for a muzzle brake and rifling of one turn for each 32 calibers.
A travel lock was located in the turret for vehicles 1 - 1,857. This was a swinging lever with a pin. From vehicle 1,858 there was a spring loaded ball stud.
Could penetrate 101 mm. Muzzle velocity 2,600 ft/sec. The AP shell weighed 15.4 lbs. It could fire a HE shell 14,000 yards.
Tank Destroyer Armament Performance