Why Britain wanted so many cruisers

Britain's demand for fifty or seventy cruisers reflected the need to control trade across widely separated seas. Cruisers and destroyers could intercept hostile merchant shipping while keeping British commerce moving. German, Italian, and later Japanese ships overseas faced capture or internment as access to normal trade routes disappeared. The estimate for Japanese merchant ships in Africa and South America is that virtually none reached home, with a possible small exception. This approach judged naval strength by its contribution to winning the whole war, even when individual battles went badly. Battleships and carriers remained necessary for fleet action, while numerous smaller warships maintained control of the water between battles.