Admiral Hiraga designed most of the ships that vaulted the IJN into prominence right after WW I. All the battleships of the "8-8" programme, including the Nagato, Akagi,Tosa, Owari, and "#13-16" (my Kii) class were designed by him, as well as the Myoko class cruisers and many other smaller ships. Above is his only design that fit within Treaty tonnage. Various reasons prevented it from being built, but by the time Japan was ready to build battleships again, newer designs took precedence.

In "Grand Fleet" the old battleship Kongo became due for replacement in 1933 after twenty years of service as allowed by a provision in the current Washington Naval Treaty. Some new concepts were tried out in Japan's first and only 35,000-ton Treaty-compliant battleship. The latest trend was to concentrate the heavy guns to save armor. The British "Saints" were the first to have this feature, followed by the Treaty-compliant Nelsons, and the French Dunkerques. The IJN specified ten 16" guns, so to save space a triple heavy gun turret made its first appearance on an IJN battleship, curiously superfiring over a more conventional twin. This somewhat top-heavy design, with its distinctive double-curved funnel, was partially compensated by taking advantage of a clause in the Treaty allowing a 3,000 ton margin for improvements for anti-submarine protection. A "bulge" was built on the bottom of the ship and filled with reinforced concrete to add a deep keel ballast.

Admiral Hiraga had just finished the design work on the secret Kii project when he attended the launching ceremony for his new battleship (named Kawachi). A pacifist assassin, thinking that if the designer of such warships were dead the warships would not get built, viciously attacked and killed the Admiral on the reviewing stand. Dead was the man who was instrumental in resolving an impasse during Treaty negotiations to allow greater tonnage to be allotted to the Japanese, and designed and oversaw the resurgence of Japanese naval power. Contrary to normal Japanese procedure the new ship was renamed Hiraga in his honor, a surprisingly Western gesture.

Hiraga went along on the Indonesian and Midway campaigns, but became part of the "Hashirajima Fleet" of warships waiting around the Home Islands ostensibly for the "Decisive Battle" to shape up. While anchored in Hiroshima Bay, a huge explosion of unknown origin wrecked Hiraga and she settled rapidly to the bottom.