The United States is not graduating enough science, technology, engineering, and mathematics (STEM) majors for the increasing number of available employment opportunities and national security needs. The purpose of this study was to quantify the magnitude of STEM attrition at the United States Air Force Academy (USAFA), a military service academy and one of the three commissioning sources of officers for the United States Air Force. Also, the study identified factors associated with STEM attrition among students. Despite strong academic preparation, of the students who reported their intention to major in a STEM discipline as incoming freshmen, 36.4% switched and graduated with a non-STEM degree. Two binary logistic regressions revealed that the best predictors associated with students graduating with a STEM major were their initial intention and motivation to major in these disciplines upon arrival at the USAFA and course grades in Calculus I, Calculus-based General Physics I, and Applications of Chemistry I. These findings suggest that, as in many other universities, students motivated to major in STEM may switch out if they struggle with prerequisite quantitative courses.