What is the latest kind of warship that could be kept operating without an industry able to build new ships?
Short answerThe Warrior and Black Prince generation is about the limit, though wooden warships would be easier to sustain.
NotesThe 1860s ironclads still carried equipment and practices intended for distant service with partial self-reliance. Later warships became too dependent on specialized industrial supply and repair systems. Even Warrior-era ships would be difficult, and a wooden warship would be the safer choice if industrial support truly vanished.