For over half a century, South Korea has provided military and para-military personnel for service in American military units. South Korean conscripts who do well enough in their high school English language classes, can do their mandatory military service in an American military unit. It's still common for 5-10 percent of the troops in American units to be South Korean soldiers. 

But there is an even larger number of South Korean soldiers assigned to the American army in wartime. This is the Korean Service Corps (KSC). The KSC troops work with American combat support units to move supplies, repair damage, build fortifications or other facilities and, considering the high percentage of South Koreans that use PCs and the Internet, help out with the growing computer networks used by American military forces. In peacetime, there are 2,185 Korean army reservists working full time to staff 15 reserve KSC companies. In wartime, 24,000 South Korean soldiers (or civilians drafted just for KSC service) and 800 reserve officers would be assigned to the KSC and the force would be expanded to 162 companies. The KSC was first established during the 1950-53 Korean War. The 15 permanent KSC companies hold regular mobilization drills to make sure everyone knows what to do it there is a war. Recently, there have been more of these mobilization drills.