The following photos are from the US Marine Corps Air-ground museum at Quantico. They were taken in Oct, 2001. Special thanks to Greg Balzer and Ken Smith-Christmas, the curator for arranging the visit.
Robert Horton notes: This is actually a 3" Naval Landing Gun of about 1880-1890 vintage. There were about five different models of these guns built in unknown quantities. Some had bronze tubes and some had steel. The boxes on the axles were to carry complete rounds of ammo and were made to be quickly unlocked and discarded and new, full boxes mounted. Most of these guns have a small wheel at the apex of the trail arms so actually, it is something of a push-around tricycle.
Robert Horton notes: This is a U.S. Pack 75 howitzer of 75mm. It is the first version and designed to be broken down into 4 or 5 loads for pack mule portage. The later version in WWII had rubber tires and was set up to be paradropped. This first model is from about late 1920's or into the early 30's.
Robert Horton notes: This is a United States 37mm trench gun often used to knock out snipers and pill boxes and M/G emplacements. This is the model of 1916.