Rebuilding dormant battleship-scale industry

Could modern industry still produce battleship-scale armour, guns and a new battleship?

Not immediately; the designs may be recoverable, but the specialised plants, machinery and tacit production knowledge would have to be rebuilt.

A modern state could not begin producing a traditional battleship immediately. Manuals may preserve formulas and procedures, but the specialised plant for thick armour, very large guns and capital-ship construction has disappeared or moved into other fields. Recreating that capability would require new machinery as well as the practical knowledge that develops only through repeated production. This industrial gap is separate from overall scientific progress, since societies can advance in vaccines, nuclear weapons or space systems while losing a particular heavy-manufacturing skill. The capability could be rebuilt, but it is not ready for instant use.