How navies learned to preserve mothball fleets

How important were mothball fleets, and how did navies learn to preserve steam-and-steel warships?

They were valuable sources of surge capacity, but long-term preservation required interwar and Cold War development of active maintenance, moisture control, and reserve crews.

The gradual transition from wooden sailing ships to steam and steel gave navies time to adapt their reserve practices. Boilers proved particularly troublesome, with some ships needing replacements after storage despite having entered reserve with serviceable machinery. Before the First World War, parts of the Royal Navy's reserve fleet returned to service for exercises, so ships were typically operated again every two or three years. Treaty restrictions and longer expected service lives then raised the prospect of leaving machinery untouched for ten or twenty years. Cosmoline and passive dehumidifier packs could not provide adequate protection over those longer periods. Postwar preservation added covers over equipment, active dehumidification, and regular patrols. At Portsmouth, crews housed aboard accommodation ships inspected the reserve vessels daily to keep them capable of eventual reactivation.