Since the warship of the New government army, Cyoyomaru, was torpedoed and sunk by the warship of the former army of bakufu (Japanese feudal government headed by a shogun), Banryumaru, in Hakodate Port, they made an attack toward the direction of Benten Daiba (Cape Benten Battery) by Hijikata's command.
箱館港では旧幕府軍蟠竜丸が新政府軍朝陽丸を轟沈せしめたため、土方に命じられて弁天台場方面へ進撃。