He went through the Austro-Prussian War as a kansenbukan (a military officer to observe military operations) where he studied international law and obtained knowledge about military affairs, shipbuilding and vessels, then returned to Japan on board the Kaiyo Maru Warship, which had been ordered by the bakufu, and after serving as a gunkangashira-nami (a post in the navy), in January 1868, after Taisei Hokan (a transfer of power back to the Emperor), he was appointed Kaigun Fuku-sosai (the vice-president of the navy), which had been Tokugawa Family's kashoku (a hereditary occupation), and became a considerably leading figure in the Tokugawa Navy.
普墺戦争を観戦武官として経験、国際法や軍事知識、造船や船舶に関する知識を学び、幕府が発注した軍艦開陽丸で帰国、軍艦頭並を経て大政奉還後の慶応4年（1868年）1月に徳川家家職の海軍副総裁に任ぜられ、実質的に徳川海軍のトップとなった。