The US Navy had enough for Cuba. The Army is short of guards?
It is a permanent need. The military operates a large number of very old and permanent prisons for military personnel including in foreign countries.
Outside of war needs and refugee needs around the entire globe, the military also has to maintain prisons for it's own criminals from it's population that is equal to that of several states combined, that includes police, prison guards, wardens and every other facet of civilian life as it relates to criminal internment for up to life and even death row prisoners.