The Soviet ISU-152 wasnt field arty, it was a direct fire cannon. Someone correct me if I am wrong, but I thought it was used as a tank destroyer more than anything, yes?
Field arty = US 105 Howitzer via jeep, 75mm pack howitzer (via donkeys, of course

); Soviet 122mm howitzer; UK 25 pounder (86mm?); Jap 7cm Type 92 Inf cannon; German 15cm Inf cannon; etc