Would like to see some of the Motorized Gun Carriage variants of the M Series...
M3A1 75 mm GMC (75mm Gun)
M21 81 mm MMC (81mm Mortar)
T19 105 mm HMC (105mm Howitzer... only had 8 rounds though)
None of them would be able to take any sort of punishment... but if you needed heavy firepower somewhere in a hurry...