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, , 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. In addition, the Imperial government received the support of two transportation ships chartered by the United States for the transportation of its troops. ==Combat==