In 1913 Tada entered Kuhara Shoji Kaisha (Kuhara Trading Company). The following year he joined Kokusai Steamship Company and ultimately became its managing director. When the company was merged with Osaka Shosen Kaisha (Osaka Mercantile Marine Company or O.S.K.) to form Kokusai Zoki Kaisha (Kokusai Machinery Manufacturing Company) Kozo became president of the new company in 1943.
Later Tada served as president of Nihon Jfikogyo Kaisha (Japan Heavy Industry Company) and director of several other companies and thereafter became president of Naigai Kaiun Sangyo Kaisha (Naigai Marine Transportation Industry Company) and president of Hatami Shipyard, Ltd.
In recent years Tada's held additional posts of managing director of Nihon Koun Kyokai (Japan Harbor Association) and Chugoku Chiho Koun Kyokai (Chugoku District Harbor Association.