Japan had an escort and anti-submarine programme during World War II. Kaibōkan means sea defence ships, a designation previously associated with obsolete vessels retained for useful defensive work. The Imperial Japanese Navy needed newer ships to fulfil the wartime escort role. Having that requirement and a programme to address it left the problem of delivering enough ships in time.
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Sea defence ships and Japan's escort requirement
Japan had a wartime escort and anti-submarine programme, while the sea defence ship designation had earlier applied to obsolete vessels retained for defensive duties.