(The things you turn up while doing searches. This page from one of the Army's own sites seems to be from 1995. 'Cost avoidance' = slave labor):

http://www.hqda.army.mil/acsim/ops/inmatebg.htm

The Army has established civilian inmate labor programs on twelve installations since FY 89. Four resident programs (prison camps) are at Fort Bliss, Fort Dix, and Camp Atterbury. Eight non-resident (off-post) programs are at Parks Reserve Forces Training Area, Red River Army Depot, Fort Lee, Fort McClellan, Fort Stewart, Fort McPherson, Fort Indian Town Gap, and Anniston Army Depot. Fort Dix has two resident programs (prison camps) using civilian inmates from both federal and state penal systems. Camp Atterbury's resident program uses state civilian inmates. These ten programs average an annual net cost avoidance ranging from $263,000 to $3,500,000....