I don’t think it is a weapon. Is this a Nam era photo?
The image appears to have been taken aboard a boat or small ship.
This widens the possibilities to many things.
I think it was a mortar of some sort, mounted on the river boats.
Edit: Found this picture of one, doesn’t look the same, but maybe different version
Actually looks very much like a match to the first picture.
It is the 60 mm mortar Mk 4 Mod. 0. Also used in single mountings.
I agree; looks like a Mark 4 Mod 0 60mm mortar.
At the Naval Ordnance Museum in St. Louis (a SLICS side trip) there are two developmental mortar rounds recovered from the Crane Naval Ordnance Depot, one for both the 60mm and one for the 81mm. Both are canister (ball shot). This would be for the direct fire mode of use. The 81mm appears to be the predecessor of the flechette round. Unfortunately the folks at the museum sometimes value display over the sanctity of the round, and drilled a hole through the center of each round to bolt them to a display. These pictures were taken prior to that happening.
Not your normal ‘white goods’
They (Whirlpool) did a lot of flechette related development back in the day. One of their former artillery test ranges was beside our demolition range in Indiana (many many years ago), we became very proficient at changing flat tires when working in the area.
Currently, at the St. Louis Ordnance Museum (Jefferson Barracks), these two cannister rounds are now seen on top of the mortar board.
I think we have 2 answers. I believe it is a 60mm.But, I was a M67 90mm recoiless gunner and it was a direct fire weapon as well. But that is TO&E for a light Infantry Weapons Squads. It is a possibility.
Interesting application of what appears to be an M60B Machine Gun (No butt stock or bipod).