The Unryu programme accepted whatever engines, gearing and armor could be obtained to produce carriers with a useful air group quickly. This reliance on available equipment is the basis for classifying them here as light fleet carriers, distinct from the more ambitious modified Taiho. Ibuki offered an existing cruiser hull for conversion, although her 1943 launch never led to service as a carrier. An air-defense cruiser is raised as another possible use of the hull, with suitable armament identified as the obstacle. Conversion to a fast oiler was also considered as Japan faced an acute shortage of those ships. An extra flight deck would have been useful only if Japan could supply aircraft and trained aviators, and aircrew had become the more serious constraint.
Chapter · 37:53-40:21
Unryu and Ibuki reveal Japan's emergency carrier choices
Japan pursued adaptable carrier hulls from available machinery and cruiser construction, but ships alone could not replace lost aircraft and trained aircrew.