"There are two kinds of soldiers at the U.S. Disciplinary Barracks (USDB) at Fort Leavenworth, Kansasโthe ones with no rank or pay, and those with keys. The USDB, unofficially called "The Castle," is the only maximum-security prison within the Department of Defense."
thebalancecareers.com/doing-time-at-leavenworth-3354200