Some of these ships are designated USNS and some are USS. I could be mistaken, but I thought all were commissioned as USNS. And as far as I know there were no modifications prior to be redesignated USS. All this said, what prompted the change to USS?
The Navy is moving away from the USNS for the ESBs.
The ESBs are all scheduled to be USS for now on.
Basically the ESBs are now being designated as warships and thus USS. This probably indicates they’ll have Navy Crews, at least partially and will carry some level of weapons. I wouldn’t be surprised if they’re thinking about Drones.
For those, like me, who’re curious what an ESB ship is, see: United States Navy > Expeditionary Sea Base (ESB) > Display-FactFiles and Expeditionary Transfer Dock → Expeditionary Mobile Base - Wikipedia.
In short, these are specialized Navy combat support cargo ships that exist sorta in the gray area between ordinary combatant vessels and pure auxiliaries. And are seemingly now being redesignated toward the combatant side.
The Navy article I cite says the designation changes are 5-10 years ago. So not really new news. And offers the minimal rationale that “This re-designation allows combatant commanders greater operational flexibility in employing the ship.”
Which in turn suggests there are laws, regulations, or rules of engagement that keep USNS-designated ships farther from harm’s way than USS ships. Or that otherwise restrict how they may be deployed and what activities they can lawfully engage in.