In 1860, Katsu served as captain of the warship "Kanrin-maru" (with assistance from US naval officer Lt. John M. Brooke), to escort the first Japanese delegation to San Francisco, California, en route to Washington, DC, for the formal ratification of the Harris Treaty. The "Kanrin Maru", built by the Dutch, was the first Japanese vessel to sail to the Western world. Kaishū remained in San Francisco for nearly two months, observing American society, culture and technology. Following his return to Japan, Katsu held a series of high-ranking posts in the Tokugawa navy, arguing before government councils in favor of a unified Japanese naval force led by professionally trained officers in disregard of promotion and assignment due to hereditary status. During his command as director of the Kobe Naval School, the institute would become a major source of activity for progressive thinking and reformists between 1863 and 1864.