Katsu Kaishū
In 1855, Nagai was transferred to the newly formed Nagasaki Naval Training Center, where he served as its director, overseeing a group of Dutch military advisors and students from various domains around Japan in studies of western warship technologies. Katsu Kaishū later credited Nagai for much of the training center's progress, as well as the construction of the Nagasaki Iron Works, and one of its training ships, the "Kottoru". In 1857, with the closure of the Nagasaki Naval Training Center, Nagai returned to Edo on board the "Kankō Maru", Japan's first steam warship, together with 103 of his students.