When the Tank Destroyer Force was organized in 1941, thye were looking for something light and fast and a heavy hitter. The M 18 was the last of a long line of guns that the US field commanders felt would be better on the battlefield not as a front line vehicle, but a way to put more guns into the field of fire and therefore increase chances of winning exchanges.
It had just a half inch of armor that would stop small arms fire, or even heavy machine gunfire. But not German guns. We used to call these gun motor carriages. The idea was to get anti-tank guns on a battlefield. OK, not every vehicle can stand down a Tiger tank. But a gun with insufficient armor is better than no gun. And the fact of the matter is that the 2500 Hellcats we built and deployed took out over 500 enemy armored-vehicle. The high velocity 76 mm gun could stop anything Gemrnay fielded, depending on the location of the shot.
Kills claimed were 526 in total: 498 in Europe, 17 in Italy, and 11 in the Pacific.
The M18 carried a five-man crew, consisting of a commander, gunner, loader, driver, and assistant driver. 45 rounds of main gun ammunition were carried, 9 in the turret and 18 in each sponson. An M2 Browning Machine Gun with 800 rounds of ammunition was provided on a flexible ring mount for use against enemy aircraft and infantry.