The Japanese System

Japan's policy has stressed sea power, but it has considered the navy not as an independent arm but as a means of supplying and protecting large masses of land troops. All Japanese men from the ages of 17 to 40 were subject to the obligation of military service in time of peace. Exception was made for convicted criminals, the physically disabled, and those who were the sole source of support for their families. The normal period of service was two years in the army and three years in the navy, but this was reduced for those who had been graduated from advanced schools.

From EM 21: Shall We Have Universal Military Training? (1944 Censored)