STU-III is a family of secure telephones introduced in 1987 by the NSA for use by the United States government, its contractors, and its allies. STU-III desk units look much like typical office telephones, plug into a standard telephone wall jack and can make calls to any ordinary phone user (with such calls receiving no special protection, however). When a call is placed to another STU-III unit that is properly set up, one caller can ask the other to initiate secure transmission. They then press a button on their telephones and, after a 15-second delay, their call is encrypted to prevent eavesdropping. There are portable and militarized versions and most STU-IIIs contained an internal modem and RS-232 port for data and fax transmission. Vendors were AT&T (later transferred to Lucent Technologies), RCA (Now L-3 Communications, East) and Motorola.

STU-III is a family of secure telephones introduced in 1987 by the NSA for use by the United States government, its contractors, and its allies. STU-III desk units look much like typical office telephones, plug into a standard telephone wall jack and can make calls to any ordinary phone user (with such calls receiving no special protection, however). When a call is placed to another STU-III unit that is properly set up, one caller can ask the other to initiate secure transmission. They then press a button on their telephones and, after a 15-second delay, their call is encrypted to prevent eavesdropping. There are portable and militarized versions and most STU-IIIs contained an internal modem and RS-232 port for data and fax transmission. Vendors were AT&T (later transferred to Lucent Technologies), RCA (Now L-3 Communications, East) and Motorola.