I think they were strictly on certain navy gunboats, and not even on all classes of them.
We traded “gathered goods” with the crews from the PBRs and barges the Navy used to convoy supplies up river...
Dual .50s were the rig of choice....
We never learned how they got access to so damned much Scotch..
They never figured out that the AKs they got in trade were the poorly make Chinese models — NEVER the better made versions from Eastern Europe. Those from the GDR were prized “booty/spoils”.