Gengo was promoted to as head of the Shogun naval fleet, but the Boshin War had already begun. After the surrender of Edo Castle, Katsu Kaishu had promised to hand over the warship to the Imperial government, but the Admiral of the Bakufu Navy Enomoto Takeaki refused to surrender, and the last remaining shogunate forces retreated including Arai Ikunosuke and Gengo. As a result of the negotiations, four warships, the "Kaiyo Maru", the "Kaiten Maru", the "Banryu Maru", and the "Chiyodagata Maru", was organized, but they were dissatisfied with the various measures taken by the new government. Enomoto decided to lead the fleet and escape after seeing the relocation of Muneya to Sunpu.