Designed near the close of WWI, this series of fast, heavily armed battlewagons was part of Japan's "8-8" program of eight battleships (Kaga, Tosa, and others) and eight battlecruisers (Akagi, Owari, and others) to give her the battle fleet she thought she needed. With two more 16" guns than their predecessors Nagato/Mutsu, they were longer and faster but less heavily armored. To meet treaty obligations, Kaga and Akagi were converted, starting in 1926, in several stages to become Japan's premier aircraft carriers. When war loomed, Tosa and Owari took turns in the dockyards, too.

Half-sisters to CV's Akagi and Kaga, these modern conversions took similar aging battlewagons and quickly made them into fleet speed aircraft carriers. Wheras Akagi / Kaga had virtually no deck armor to stop bombs or plunging fire, the new conversions had three inches at hanger deck level over both fuel and magazines. The waterline casemates were elminated, and both the quarterdeck and forecastle side plating was raised for better seakeeping. The hanger was extended both fore and aft and the working air complement raised from 78 to 89 aircraft. Though sister to Akagi, Owari dispensed with the port-side island, and, along with Tosa, had stack gasses trunked to a now-standard starboard island. Akagi and Kaga were scheduled to be similarly refitted, but war intervened and the original pair was sunk at Midway.

While Tosa was working up in the Inland Sea, Owari went on the Hawaiian Operation, and her planes sank the battleship Nevada and some submarines. When the American carrier fleet made its surprise appearance, Owari received bomb damage but managed to cripple the Yorktown before fleeing to Truk. Still damaged, she met up with Tosa for the Midway Operation. She only had her aft elevator working, and was therefore used strictly as a fighter carrier, cycling through the fleet's CAP from various other carriers--a convenient spare flight deck (if only Zuikaku had been so used for the historic Midway operation....?) Subsequently, the two of them headed west to Ceylon, where British Hawker Henley dive bombers from Excalibur sank the Owari. Tosa soldiered on through many Pacific campaigns but was sunk in 1944 fighting the renascent seapower of American wartime construction.