For the operation, an Imperial Japanese Navy fleet had been rapidly constituted around the recently acquired ironclad warship Kōtetsu (the former Confederacy CSS Stonewall), which had been purchased from the United States.

Other Imperial ships were Kasuga, Hiryū, Teibō No.1, Yōshun [ja], and Mōshun, which had been supplied by the domains of Saga, Chōshū and Satsuma to the newly formed Meiji government in 1868.

The nascent Imperial government started with a much weaker navy than that of the Ezo Republic, both in terms of vessel strength, unity (most of its ships were borrowed from Western domains), and training.

However the loss of two major units on the Ezo side previous to the main action (Kaiyō Maru and Kanrin Maru), and most of all, the incorporation of the revolutionary Kōtetsu since April 1868 on the Imperial side (a ship originally ordered by the Tokugawa shogunate but withheld by the United States during the main conflict under a policy of neutrality taken by foreign nation and finally delivered to the newly formed government), turned the tables.

The future Admiral of the fleet Tōgō Heihachirō participated in the battle on the Imperial side as a young third-class officer, onboard Kasuga.