The Joint Advisory Commission, Korea (JACK) was a U.S. covert operations unit that participated in the Korean War.
Operating under the direction of the Central Intelligence Agency, JACK was responsible for inserting and extracting U.S.-trained Korean agents into North Korea, conducting covert maritime raids along the North Korean coast, and providing escape and evasion support for downed Air Force pilots.
References
Joint Advisory Commission, Korea Wikipedia(Text) CC BY-SA