The Korean Military Advisory Group (kmag) – a relatively small unit of U.S. Army officers – developed, advised, and exerted influence over the Republic of Korea (rok) Army from its inception in 1946 through the signing of the Korean War armistice in July 1953. kmag advisors served down to the battalion level, working alongside South Korean counterparts in rok Army units, causing language to be a crucial battlefield that animated American anxieties and negative racial assumptions. In a moment when few, if any, American military officers had Korean language proficiency, South Koreans with English-language capability became essential to the U.S. foreign policy project in South Korea. South Korean interpreters, too, amplified racialized concerns about the trustworthiness of rok soldiers. This article places American understandings of language in kmag affairs into critical focus, highlighting the cultural assumptions that came to effect material change in U.S. Army policy towards the rok Army before and during the Korean War. It shows how language was a means of U.S. penetration into the fabric of Korean state and society, but also a target of imaginations that disturbed the U.S. military because of its consistent reminder of how language could resist American suggestion.