朝鮮戦争休戦協定
On 27 July 1953, the Korean Armistice Agreement was signed, launching Operation Big Switch, the repatriation of Korean War POWs. (Ultimately, some 12,773 UN POWs were repatriated.) Twenty-one American POWs refused repatriation and defected, and the returning POWs were viewed as potential security risks. As a result, debriefings became "hostile investigations in search of possible disloyalty".