Robert Farley
Over the years, a variety of reports of turned up on the expected successor classes to Yamato. The next iteration would have been slightly larger, slightly more heavily armored, and would have carried six twenty-inch guns in three twin turrets, probably with roughly the same speed and range as Yamato. Designs for these ships were finalized, but wartime demands meant that they were never laid down. Indeed, the effort that went into Musashi’s construction would better have been spent on aircraft carriers and other ships. Expectations of a further follow-on class, with a speed above thirty knots and four twin twenty-inch guns, have emerged over the years, although the construction of such ships would have been purely notional.
Japan withdrew from the London Naval Treaty in 1936. The chief Japanese negotiator, Adm. Isoroku Yamamoto, feared that concessions on the part of his negotiating team would lead directly to his assassination upon return to Japan. Japanese nationalists believed that the Washington Naval Treaty system was holding Japan back and preventing it from becoming a first-rate power. Freed from the constraints of international treaties, they believed that Japan could build a world-beating fleet that would push the Western powers out of Asia and help usher in a new era of Japanese dominance.
http://nationalinterest.org/blog/the-buzz/japans-huge-world-war-ii-battleships-were-monsters-almost-22597
