M47. Not really a WWII vehicle - didn't enter service until 1950, never saw action in US service. Superseded by the M48 in ... 1953? I think? Basically an M26 chassis with the turret from the (experimental, never produced) T-42 heavy tank.
I thought it was a variation of the R-35 at first.
It's the SAu-40?
Yup.