Mine warfare as a lesson not fully carried forward

First World War experience showed mines to be exceptionally disruptive as well as destructive. A minelaying submarine could lay weapons off a harbour approach, leave, and continue attacking elsewhere while the mines remained active. Their effects included repair work, harbour blockage, route clearance, and delays to convoy schedules. HMS Belfast's early-war mine damage illustrates how one weapon could remove a major cruiser from operations for an extended reconstruction. This burden is contrasted with the narrower Second World War emphasis on torpedo attack, raising the question of why Germany and Japan did not exploit long-range minelaying submarines more fully.