This actually happened when they brought the Iowa-class battleships out of mothballs in the 80's. They found out that the 16" guns needed to be re-barreled. In

This actually happened when they brought the Iowa-class battleships out of mothballs in the 80's. They found out that the 16" guns needed to be re-barreled. In order to make new ones, they'd either have to have them made in places like Japan or Germany (ironic, eh?), or rebuild a significant portion of the US steel industry (they had gone to mini-mills, which can't produce a forging that size). Luckily they found some in a warehouse left over from WW-II.