This paper combines novel archival research with a re-reading of the existing documentary record to reframe and investigate “the POW/MIA issue” as an ideological phenomenon. Prior research on the POW/MIA issue, or the widespread, persistent belief that US prisoners of war were secretly held in Vietnamese custody for years after the official 1973 prisoner swap, treats its persistence as the outcome of voluntarist factors like fraud and gullibility or the energy and innovation of grassroots activists. In contrast, this thesis argues that the issue's persistence in American political discourse is an artifact of the US national security state's ideological functions. It accomplishes this argument by first casting the National League of Families of Prisoners and Missing in Southeast Asia as an ideological state apparatus, then demonstrating that the League modeled a specific kind of state-sanctioned POW/MIA subjectivity organized through the feeling I call autonomic certainty, or the use of intense feeling as proof in-and-of-itself. The POW/MIA activism of Ann Fischer, a rank-and-file League member from Madison, WI, stands as an example of autonomic certainty in action. Ann’s brother, US Marine Richard W. Fischer, was declared MIA in Vietnam in 1968, sending members of the Fischer family into a years-long quest to prove he was alive in captivity. Meanwhile, the Department of Defense withheld convincing wartime evidence that Richard Fischer was killed and buried on the day he disappeared. This thesis is the first piece of POW/MIA literature to stake its claims with DOD case files relating to a POW/MIA.