That would imply that Musashi never had any 5" (127mm) guns at all?? I really would suggest some double-checking. I'll pull out Conway's All the World's Fighting Ships 1922-46 and Jenschura et. al. Warships of the Imperial Japanese Navy and see what else I have around the house. We also have a couple of references from combinedfleet.com: Yamato-class Battleship | Nihon Kaigun Best Battleship: Secondary Batteries Here's another quickie from http://www.scharnhorst-class.dk/scharnhorst/history/scharncerberus.html: "the complements of the two battleships had been augmented by detachments of naval coastal gunners - sailors who normally never went to sea, but whose 20 mm quadruple-mounted guns were intended to strengthen the anti-aircraft defences." Since the quad 20mm was fired manually/optically by a gunner on-mount, it could just be bolted or welded to the deck and be ready for action. Heavy flak guns, to be worthwhile, would have to be integrated with a director system and stable element. There were cases like Yamato or HMS Malaya when additional guns of the same type already carried (5", 4") were added, but these were permanent installations. Which reminds me, the suggested interpretation of Breyer would also imply that Yamato as built did not have those four Type 94 AA directors, and that they too were worked in when the midships 6.1" turrets were removed?