The Kaga class battleships were to be improved Nagato class were ordered in the 1918 Program to be part of the 8-8 Project (8 battleships / 8 battlecruisers).
Y. Hiraga was the designer of the Kaga class.
It was intended that the Kaga class would carry ten 16" guns.
The terms of the Washington Treaty of 1921 said that the uncompleted Kaga class battleships had to be destroyed. Both had already been launched and the Tosa was used as a target and the Kaga was converted into the IJN Kaga aircraft carrier.