In January 1988, a new policy was instituted that reduced the age-group of the male population subject to service in the reserves: only males who had been drafted for service between the ages of nineteen and thirty-four were required to serve in the reserves. The period of service was limited to between six and eight years, depending on the individual's age at conscription.The mission of the mobilization reserves was to provide each of the services with well-trained personnel prepared to enter combat as soon as possible in wartime.
In 1990 there were 1,240,000 men in the reserves: 1,100,000 in the army; 60,000 in the marines; 55,000 in the air force; and 25,000 in the navy. Most recruits had served on active duty in their respective services and were assigned to a reserve unit upon completion of their term of enlistment. Units in the reserves probably closely resembled active-duty organizations. Mobilization reserve personnel attended regularly scheduled training about one day a month and also participated in an annual field exercise that lasted about one week.
Active-duty officers and NCOs were assigned to command and staff positions in the reserves at battalion and higher levels.The Homeland Reserve Force was established in April 1968 as part of a nationwide program to increase defense preparedness in the wake of North Korean provocations. In January 1968, a North Korean commando unit infiltrated Seoul and attacked the Blue House in an attempt to assassinate President Park Chung Hee.
That same month, two additional North Korean commando units launched attacks on towns on the east coast in attempts to encourage the South Korean populace to overthrow the government. Homeland Reserve Force personnel were given basic training in physical fitness, weapons familiarization, and defense tactics against various types of attacks by enemy forces. In wartime these units would remain close to or in their own cities, villages, or towns, where they would guard roads, power plants, factories, and other potential military targets.
In 1975 the National Assembly passed the Civil Defense Law, which was promulgated to establish organizations in every community to protect lives and property during wartime and natural disasters. Males between the ages of nineteen and fifty who were not drafted for service in the military were recruited for service in civil defense units. In 1980 there were over 90,000 civil defense personnel in the country. By 1990 their numbers were more than 3.5 million. Their missions included air raid defense, search and rescue, and building and road repair.
Data as of June 1990
Source : http://www.mongabay.com/history/south_korea/south_korea-reserve_and_civil_defense_forces.html