I photographed these M1918 155mm Howitzer variants at Fort Lewis and Camp Shelby. There is also a M1918A1 Howitzer at Ft Lewis that might belong on this page at some point.
M1918 155mm Howitzer and Caisson
I now think there may have been some confusion as to whether the Caisson and the Howitzer were meant to be displayed together or if they are two completely separate artifacts.