What would Yamato gain and lose by replacing its mixed secondary battery with thirty-six 5-inch/40 Type 89 guns in eighteen twin mountings?
Short answerIt would gain stronger anti-aircraft fire and broader defensive coverage, while reducing the secondary battery's surface-fighting role largely to high-explosive fire against cruisers.
NotesThe proposal replaces twelve 6.1-inch guns in four triple turrets and twelve 5-inch guns with thirty-six 5-inch/40 Type 89 guns in eighteen twin mountings. More dual-purpose mountings would strengthen anti-aircraft fire and allow more defensive zones to be covered. The cost would be a weaker secondary battery for surface fighting. Against light and heavy cruisers, its usefulness is described mainly in terms of covering the target with high explosive.