It was fast, and had a 75mm gun (same as the Firefly, maybe?) but it was so lightly armored that machine guns could and did penetrate its 1-inch armor. Troop commanders didn't understand it was NOT a tank, and tried to send it in first with infantry behind, and they would be lost quickly.
In AH it'd be a sitting duck to anything including an M8.
Actually, it'd kind of be like an up-gunned M8 in performance, I'd bet.
M18s had the best kill to loss ratio of any western Allied armored vehicle. It was armed with the M1 76mm gun shooting HVAP ammo, which could penetrate a Panther's front armor at 1,000 yards. These things were extremely lethal. They were generally used to ambush German tanks, then use their 60 mph speed to reposition. Their armor could keep out machine gun rounds and 20mm as well. The armor was well sloped and lacked the shot traps common to most tanks of the era. Its low silhouette, rapid fire gun, fast revolving power turret and blinding speed made it a very dangerous and slippery enemy. German tank crews hated the Hellcat, because if you didn't get off the first round, you weren't likely to live long enough to get off the second one. M18s were too fast to engage in a running fight. They would be behind a tank long before it could traverse its turret. M18s usually operated in pairs, which really made them tough to deal with.
At St.Vith, two M18s killed more than a dozen Panthers, MkIVs and APCs in about 10 minutes. Supported by several M10s, Shermans and 90mm anti-tank guns, they beat the living snot out of German armor for several days. The German's failure to take St.Vith without a major engagement crushed their timetable. More-so than the defense of Bastogne, the defense at St.Vith sealed the fate of the German offensive. The newly arrived M18s were a critical part of the Bulge defense.
Some historians rate the M18 as the best tank destroyer of the war. Some were still in service into the middle 1970s.
My regards,
Widewing
