Which navy would have benefited most from an equivalent to the Royal Navy's Black Swan class?
Short answerThe Imperial Japanese Navy, because it needed a specialist escort and team to lead its broader anti-submarine force.
NotesThe Imperial Japanese Navy is the preferred candidate for a Black Swan-style escort in this comparison. Japan already had some useful escort ships. The proposed addition would provide a highly proficient escort team to lead them. That team would strengthen specialist leadership within the existing force.