According to information on display in 2005 at the NSA's National Cryptologic Museum, the STU-II was in use from the 1980s to the present. It uses the linear predictive coding algorithm LPC-10 at 2.4 kilobits/second to digitize voice, and the "Key Distribution Center" (KDC) for key management. The display also stated that the STU-II B is the standard narrow band secure telephone. Some 10 000 STU-II units were produced.