What the hell is an “offshore support vessel”?
They’re called sub tenders, and are specifically used for underway replenishment and repair for subs.
It may be one of these:
https://en.wikipedia.org/wiki/RiverHawk_OSV_60
They appear to be a multifunction support for riverine, SEALS, coastal patrol, etc...
I am speculating, but it may have been escorting the boomer out to the open sea.
“What the hell is an “offshore support vessel”?”
Probably one of these:
https://en.wikipedia.org/wiki/RiverHawk_OSV_60
200 feet long, well deck with two fast attack boats; armed with a 30mm main gun and an assortment of machine guns. Crew of 26 with 40 passengers.