Ok I'll admit that I was a dumbass and forgot to look at the plaque on this one as we were kinda short on time. So until I'm told other wise I'm going with M53 HMC even though the gun looks WAY too long and big. The M53 HMC was a self-propelled artillery vehicle armed with a 155mm M46 Howitzer and used as many parts as possible to the M46 and M47 Pattons. Although based on the tanks its armor was anything but, with a maximum construction thickness of 25mm the armor would ve enough to only with standad 7.62 rounds and lower along with shrapnel from counter battery fire. The vehicle was made in 2 main versions, the M53 (possibly shown here) and the M55 armed with a 203mm M47 Howitzer hich was significantly shorter than the 15mm M46. A .50 Caliber Machine Gun would commonly be mounted on the commanders hatch with 900 rounds available. Even though the turret looks large it only has space for 20 rounds of ammunition and 20 charges and the M55 has room for only 10 of each. The vehicles although used heavily in Vietnam were replaced by the more open M110 which would see service until the Persian Gulf War while the last M53/55 would see service with the US in 1969.

Edit: Went back to the park on 05-04-2021 and found out its a T-162 Howitzer Motor Carriage.