232051986355 -- 1920s Railwaygun 240-mm Schneider. US ?
As Lee said, this is actually the rare M1919 16-inch/50 caliber gun, emplaced only in the areas of Boston, New York City, and Oahu, Hawaii. From the vegetation this looks like Hawaii, which would be Fort Weaver. There was also a unique disappearing version on Great Gull Island, New York. The simultaneous existence of 240mm M1918 Schneider-type howitzers on fixed mountings in Hawaii may be the reason for the erroneous caption.
232051997989 -- 1942 US artillery Bataan breech shown.
This looks like it’s on a disappearing carriage in a fixed emplacement, which would make it larger than 3-inch and emplaced almost anywhere in the Manila Bay and Subic Bay areas except Bataan. The attachment of the breech yoke above the gun’s centerline is unusual. Comparison with photos in “American Seacoast Defenses” shows that it’s possibly a 14-inch disappearing gun on the M1907 carriage, which would put it at Forts Frank or Hughes, on Carabao and Caballo islands.
391533914807 -- WW2 USA monument or coast artillery cannon.
As Lee said, this is probably a 7-inch ex-naval gun, two of which still exist at Fort DeRussy, Hawaii, formerly emplaced for coast defense in WW2 in the Pearl Harbor area.
111161287652 -- WW2 British super heavy 8 inch gun CD of pictures.
This looks like the US-origin M1 8-inch gun.
122075372102 -- WW2 US strange turret with big gun in Hawaii. ?
The captions indicate this photo set is in Guam. One photo shows what looks like a 90 mm gun on the T3/M3 shielded coast defense mounting.
252487048020 -- 1967 US jeep with recoiless gun fires. 3 inch?
This is the M40 106 mm recoilless rifle.