Roughly 500 faculty members are evenly divided between civilian professors and military instructors. The civilian professors nearly all have a PhD and can be awarded tenure, usually upon promotion from assistant professor to associate professor. Fewer of the military instructors have a PhD but nearly all have a master's degree. Most of them are assigned to the Academy for only two or three years. Additionally, there are adjunct professors, hired to fill temporary shortages in various disciplines. The Adjunct Professors are not eligible for tenure.