Well, as is posted on a multitude of Kaga and Akagi images, they were originally going to be battleships before the treaties' limitations came into effect. In Kaga's case, she was to be a Tosa-class.
Actually Tosa Class Battleship, but because the treaty, both Tosa class battleship will be scrapped, but thank the earthquake, Amagi is serious damage, so Kaga is choose in Amagi's place instead and become Aircraft Carrier with the hull still of a battleship (Tosa is still was scrapped), usually is called Kaga-class aircraft carrier or Tosa-class aircraft carrier is still valid.
Actually Tosa Class Battleship, but because the treaty, both Tosa class battleship will be scrapped, but thank the earthquake, Amagi is serious damage, so Kaga is choose in Amagi's place instead and become Aircraft Carrier with the hull still of a battleship (Tosa is still was scrapped), usually is called Kaga-class aircraft carrier or Tosa-class aircraft carrier is still valid.
Tosa isn't scrapped, She was used as test target for the development of belt armor. And she was scuttled in the end.
