Railguns wait on shipboard pulsed power

How long before railguns or coilguns can be fitted to warships?

Not until ships gain much stronger generation, energy storage, and repeatable pulsed-power systems, or move broadly to nuclear power.

Practical naval railguns depend on the ship's power architecture. Abundant nuclear generation is one possible route, but generation alone does not solve the short, intense demand of a shot. Ships also need much better energy storage and cyclic power delivery so they can charge, fire, and recover repeatedly. An electromagnetic gun cannot simply be attached to a conventional hull once the barrel and projectile work in isolation.