STU-III (Secure Telephone Unit - third generation) 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 is the last of a series of digital Secure Telephone Units (STU), developed in 1987 by the US National Security Agency (NSA) 1 for secure voice communication over non-secure analogue PSTN telephone networks (POTS).

SECURE TELEPHONE UNIT, THIRD GENERATION (STU-III): The STU-III Type 1 terminal is a dual-purpose telephone capable of transmitting voice and data. It may be used as an ordinary telephone that operates over the public telephone network.

STE sets look like ordinary high-end office desk telephones and can place unsecured calls to anywhere on the public switched telephone network (PSTN), as well as secured calls on it via the phone's backwards compatible STU-III mode.

SECTEL was a range of secure telephones for use on analogue PSTN networks, manufactured by Motorola in Seguin (Texas, USA). Some SECTEL models are STU-III compatible and are based on the 1986/1987 STU-III standard, developed by the US National Security Agency (NSA).

The 1100 was a third generation Secure Telephone Unit (STU-III), developed in the US by the National Security Agency (NSA) around 1987 and introduced by AT&T (later: Lucent) in 1992.

STU-III operates in full-duplex over a single telephone circuit using echo canceling modem technology. STU-IIIs come equipped with 2.4 and 4.8 kbps code-excited linear prediction (CELP) secure voice. Secure data can be transmitted at speeds of 2.4, 4.8, and 9.6 kbps.

The STU-III is the last of a series of digital Secure Telephone Units (STU), developed by the National Security Agency in the United States, allowing secure voice communication over non-secure analogue telephone networks. The STU-III was …

Motorola STU-III Secure Telephones (SECTEL) are secure voice/data telephone terminals. The STU-III/A is a version of the STU-III family designed for use within the NATO community. It contains all the basic STU-III functions and capabilities, while adding the …

The STU-III Type 1 terminal is a dual-purpose telephone capable of providing secure and nonsecure voice and data capabilities. Use the Type 1 terminal as an ordinary telephone. The Type 1 terminal is interoperable with the public telephone network.