Sloops and aviation support ships as Britain's best prewar investment

What should the Royal Navy have invested in before World War II for the greatest wartime benefit?

Large numbers of treaty-exempt sloops, supported by aviation maintenance ships such as Unicorn, would have transformed convoy escort and fleet availability.

Matching annual destroyer construction with 16 to 18 sloops could have produced roughly 160 to 180 modern ASW escorts by 1939. Because the treaty system treated sloops and aviation support ships differently from major combatants, Britain could expand these forces without triggering the same tonnage contest. That reserve of escort strength might save ships such as Royal Oak and Courageous, improve carrier availability, and strengthen the Taranto force. Starting the war with escorts already in service also reduces pressure to pause capital-ship and carrier construction for emergency convoy needs.