I also find it interesting that as the Pacific War went on, the 20mm was discarded for the heavier hitting power of the 40mm. But, as the kamikaze threat increased, the 40mm was in turn seen as too small and lacking hitting power, with the 3" becoming the calibre of choice. Add in the greater effects a larger shell can carry, I can't see how replacing the 5" with a 57mm is a sensible idea. Most AShM are bigger and faster than a IJN aircraft; add in the range and different warheads and I think 5" has decades left