Born at the Saga domain mansion in Edo, a son of the ninth lord Nabeshima Narinao. From childhood the Confucian scholar Koga Kokudō served as his tutor, teaching him learning and the resolve to reform the domain's government. Kokudō's teaching had a great influence on Naomasa's later reforms.
He succeeded his father as the tenth lord of Saga domain. The domain was deeply in debt, and it is said that when he first set out for Saga, creditors crowded into the Edo mansion and his procession could hardly leave. Carrying this humiliation in his heart, Naomasa resolved to rebuild the domain.
From around this time he rebuilt the domain's finances by cutting the number of officials, enforcing strict economy and renegotiating how debts were repaid. He also increased income by fostering industries such as porcelain (Arita ware), coal and wax. The reforms met resistance from retainers but bore fruit little by little.
He expanded the domain school Kōdōkan and made study compulsory for retainers' children, and is said to have been so strict that those with poor results could not hold posts. From this school came Ōkuma Shigenobu, Etō Shinpei, Soejima Taneomi, Ōki Takatō and others who later played leading roles in the Meiji government.
To spread vaccination against smallpox, he had cowpox vaccine obtained through the doctor of the Dutch trading post, and first had his own son Jun'ichirō (later Naohiro) vaccinated. Because the lord's son had received it, people's fears eased, and vaccination spread from Saga to other regions.
Saga domain, charged with guarding Nagasaki, keenly felt the need to prepare for foreign warships. Using Western books as a guide, Naomasa had Japan's first practical reverberatory furnace built and, after many failures, succeeded in casting iron cannon. Later the domain also supplied cannon for the shogunate's Shinagawa batteries.
He created the Seirenkata, an office for research into Western science and technology, where chemistry, machinery, steam engines and more were studied. By gathering talented engineers from many regions without regard to rank, he made Saga one of the most technologically advanced domains in Japan.
He sent many retainers to study at the naval training center the shogunate opened in Nagasaki. Later he set up a naval training and ship-repair base at Mietsu in the domain (the Mietsu Naval Dockyard) and built up a Western-style navy. Naomasa was so interested in new technology that he went aboard foreign warships himself to inspect them.
He handed the lordship to his son Naohiro and retired, taking the name Kansō, but in practice he kept guiding the domain's government and technical research. Because he avoided deep involvement in the fierce politics of the late Edo period and concentrated on building up the domain's strength, he is said to have been called "the phantom of Hizen."
At the Mietsu Naval Dockyard, the domain completed the Ryōfūmaru, Japan's first practical domestically built steamship. It embodied Naomasa's idea of not just buying ships from abroad but building them with their own hands, and became a landmark in the history of Japanese shipbuilding.
Saga sided with the new government, and in the Boshin War the domain's modern weapons and troops proved a great force. In particular, Saga's Armstrong guns are said to have been used in the battle against the Shōgitai at Ueno. The domain's technical strength helped open the new age.
In the new government he was appointed the first head of the Kaitakushi, the office for developing Hokkaidō. He was keenly interested in developing the northern lands, but for reasons including his health he soon left the post, and afterwards supported the new government as Major Counsellor and in other posts.
He died of illness in Tokyo. Naomasa's reforms, which restored Saga's finances and modernized the domain through investment in education, science and technology, were carried on into the modernization of Meiji Japan through the people and techniques he fostered, such as Ōkuma Shigenobu.
Soejima TaneomiEtō ShinpeiŌkuma Shigenobu
Ogata KōanHotta MasayoshiSakuma ShōzanIi NaosukeYoshida TōyōShimazu HisamitsuIwase TadanariAbe Masahiro
People of the Edo period ・ People by period
Based on facts found in textbooks and biographies. Uncertain points are marked as such.