Why not fit twin Bofors or twin 57-mm guns to a modern escort?
Short answerTwo guns impose more maintenance, but their extra firepower and redundancy become important when a ship may fight alone and outnumbered.
NotesBAE replaced a proposed twin 57-mm arrangement with a single gun because customers did not want the maintenance burden of two weapons. That economy is easier to accept when a navy expects several ships to fight together. A lone escort facing multiple threats benefits more from the redundancy and volume of fire offered by twin mounts. The exchange connects apparently small armament choices to fleet size, operating assumptions, and peacetime support costs.