According to the old family bible, he was in 628th Tank Destroyer Bn (website about them here http://www.5ad.org/units/628td.html )
Initially TD battalions were a mix of towed AT guns and self propelled AT guns (called Gun Motor Carriages). These GMC were built on the M4 tank chassis and had thin, angled armor. These GMC in the M10-M10A1 series had open topped turrets and the 3-inch gun M7. Armor was sacrificed for speed. Unfortunately, this did not work because the TDs were pressed into service as tanks (they looked like them, but they weren't). This put the TD at a tactical disadvantage because it was to operate from ambush and not perform the assault role the tanks were to do.
Heavier German armor encountered in the Medirerranean Theater of Operations (and later European Theater of Operations) resulted in the upgrade of the M10s to a bigger gun. The rebuilt M10s were called M36s and carried the 90mm gun M3 in a larger, redesigned turret. The new 90mm gun helped level the battlefield when it came to knocking out the Tigers and Panthers, but did nothing to remedy the weak armor and lack of overhead protection for crewmen.
The M36 came in three distinct versions:
M36 — 90mm gun turret on 3” GMC M10A1 hull (M4A3 chassis) (1,298 produced/converted).
M36B1 — 90mm gun turret on Medium Tank M4A3 hull and chassis (187 produced/converted).
M36B2 — 90mm gun turret on 3” GMC M10 hull (M4A2 chassis, diesel) (287 produced/converted).
Total of all M36 produced/converted: 1,772.
Information regarding the location and operation during the Offensive can be found here.