Major Hisataka kuroda of Imperial Army who took a key role of Tokyo Defense Planning and issued jointly“Zenkoku Bougyo Houan” or National Defense Bill in Meiji 8(1875). Since then this plan was said to be the base for the construction of Tokyo Bay Fortress.

Since the effective range of the cannon at the time of the comple- tion of the No.1 Kaihou (No.1 Sea Fort) was about 3km, the Imperial Army decided to augment two sea forts between Futtsu and Kannonzaki in order to strengthen the defense and prevent the invasion of enemy ships.