薩長同盟
Anticipating that the Imperial fleet was en route to invade Ezo, Enomoto Takeaki decided to dispatch his three warships under the command of "Kaigun bugyo" Arai Ikunosuke in a boarding operation to seize the revolutionary new warship "Kōtetsu", which would severely cripple the Imperial forces and would buy time for the Republic of Ezo to prepare for invasion or to negotiate more favorable terms with the Satchō Alliance.