In the OP's defense, I see this usage increasingly, as in designating any combatant ship as a "battleship" (even being used for sailing ships). It's not correct, but then neither is "alright" in place of "all right": the language changes whether we want it to or not.

Both the words "Battleship" and "War ship" are used by DRH to describe USS Oscar Austin, so I used the same.

I did not know about distinction, so TIL!