Where cross-Channel and railway guns came from

Which ships supplied the cross-Channel and railway guns, and were spare barrels used?

Few came directly from ships; most were coastal or railway pieces, spare barrels, or guns originally intended for unbuilt vessels.

The cross-Channel batteries combined coastal guns, railway artillery, conventional land pieces, and naval-pattern weapons in many calibres. Most were built for those land roles or drawn from spare stocks rather than removed from active ships. Germany installed guns intended for cancelled vessels, considered spare Bismarck-class barrels, and reused French First World War railway artillery. Italian, Soviet, and Japanese choices show that railway artillery remained an interwar option, although Germany pursued it on the largest scale.