A January 1938 discovery leaves enough time for work to begin by March and finish around the outbreak of war. Destroyer turbines and boilers were already being ordered on a comparatively repeatable production basis, making them easier to add than bespoke cruiser machinery. Upper-deck 4.7-inch mounts also avoid the deep structural alterations required by a between-decks weapon. Once commissioned, the ships could support North Atlantic patrols, escort Norway-bound convoys, or release modern cruisers from distant stations for more demanding work.
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September 1939 availability and early-war jobs
The rebuilt ships could plausibly enter service by September 1939 because their conversion draws on destroyer machinery and avoids a between-decks gun installation.