It's the AFV version of the M1A1 Pack Howitzer, the M3 I believe. The M8 Scott HMC (M5 Chassis, and the same turrent as the LVT4) carried HEAT and smoke rounds.
LVT's used when crossing the Rhine did carry some HEAT rounds, dunno about smoke though. I don't think they carried anything other than HE in the Pac tho