The incident I’m recalling from the Bulge was that the M-18’s succeeded in ambushing a column of Mark V Panthers. Mostly the tigers couldn’t get past Bastogne on account of narrow roads, demolitions, etc. They basically ran out of fuel and we’re abandoned.
I’m not certain, but I think you are recalling a slightly earlier incident at Arracourt, France. To quote Wikipedia and save myself some typing:
“On September 19, 1944, in the Nancy bridgehead near Arracourt, France, the 704th Tank Destroyer Battalion was attached to the 4th Armored Division. Lt. Edwin Leiper led one M18 platoon of C Company to Rechicourt-la-Petite, on the way to Moncourt. He saw a German tank gun muzzle appearing out of the fog 30 feet away, and deployed his platoon. In a five-minute period, five German tanks of the 113th Panzer Brigade were knocked out for the loss of one M18. The platoon continued to fire and destroyed ten more German tanks while losing another two M18s. One of the platoon’s M18s commanded by Sgt Henry R. Hartman knocked out six of the German tanks, most of which were the much-feared Panthers.”
Fifteen kills, mostly Panthers, for the loss of three Hellcats.
At the Bulge, Hellcats were far more mobile - while they did setup in ambush, as their doctrine dictated, there were also documented running gunfights and multiple confirmed Tiger kills. Again, quoting Wikipedia so I don’t have to type about the exploits of Team Desobry and others - M18s did in fact face Tigers in combat at the Bulge:
“The M18 Hellcat was a key element during World War II in the Battle of the Bulge. On December 19–20, Team Desobry, a battalion-sized tank-infantry task force of the 10th Armored Division was assigned to defend Noville located north-northeast of both Foy and of Bastogne just 4.36 miles (7 km) away. With just four M18 tank destroyers of the 705th Tank Destroyer Battalion to assist, the paratroopers of 1st Battalion of the 506th Parachute Infantry Regiment attacked units of the 2nd Panzer Division, whose mission was to proceed by secondary roads via Monaville (just northwest of Bastogne) to seize a key highway and capture, among other objectives, fuel dumps—for the lack of which the overall German counter-offensive faltered and failed. Worried about the threat to its left flank in Bastogne, it organized a major joint arms attack to seize Noville. Team Desobry’s high speed highway journey to reach the blocking position is one of the few documented cases in which the top speed of the M18 Hellcat – 50 miles per hour (80 km/h) – was actually used to get ahead of an enemy force.
“The attack of 1st Battalion and the M18 Hellcat tank destroyers of the 705th TD Battalion near Noville together destroyed at least 30 German tanks and inflicted 500 to 1,000 casualties on the attacking forces, in what amounted to a spoiling attack. A Military Channel historian credited the M18 destroyers with 24 kills, including several Tiger tanks, and believes that in part, their ability to “shoot and scoot” at high speed and then reappear elsewhere on the battlefield, confused and slowed the German attack, which finally stalled, leaving the Americans in control of the town overnight.”
There were also witnessed and documented incidents at the Bulge where M-18s did what would later be called “Monty Pythoned” or “circle-strafed” several Tigers. The M18 was faster than the turret rotation of the German heavy, so if the Tiger gun wasn’t pointed at the M18, the Hellcat could race out into the open field and closely flank the Tiger ahead of the Tiger (or a Panther) being able to bring its gun to bear. It could literally run rings around any German armor - and at least at the Battle Of The Bulge, was documented as actually doing so.
The “50mph” limit quoted is somewhat inaccurate. 55mph was spec speed, but individual examples were known to be much faster. There’s a documented example where a Hellcat and a Jeep were isolated and had to relocate quickly during the Battle of the Bulge. Both got back to a road and floored it - and the Hellcat left the Jeep in its dust. A couple were reportedly clocked at 60+ mph.
The M18, in the context of WW2, was a fearsome little lightly armored box with a high velocity variant of the 76mm gun on top that was faster than hell and given the chance to engage on its own terms would rape any opposing armor. With “on its own terms” being surprisingly flexible.