These two pieces are part of a park in GTMO. The first two are just below 3" in bore size. Another neat feature is the rear wheel flips up and into the rear. The second I thought was a M1916, but comparing it to photos found on a google search makes me think it is something else.

The first one:






The 75mm/3" gun:




Age, rust, heavy paint jobs, and neglect have obscured any identifying plates or marks on the guns.

I don't think the first one is a US piece. The second one looks like it could be an M101A1 105mm but without the wheels. The barrel looks too short, so I am not positive about that.

The second one's muzzle bore is about 3". I didn't have a ruler, but a rough measurement puts it about there. I am wondering if it is an old WW1 gun that got a new carriage for WW2.

Irish,
All the old pieces I've seen had the MK MOD stamped on the edge f the muzzle.

Even if it's covered in paint you may be able to put a sheet of paper over it and use a pencil to get and impression and try it from there.

The first tube looks like a three inch/75mm gun from around WWI...

I'll try the rubbing method. But I still think the top piece is foreign made. Maybe not Spanish-American War vintage, but maybe.

maybe a version of the 3-inch field gun M1902 (76.2 mm)
https://en.wikipedia.org/wiki/3-inch_M1902_field_gun