What type of communication device encrypts voice communications using an algorithm?

The device that encrypts voice communications using an algorithm is the STU III. This device is specifically designed for secure voice communication, incorporating cryptographic algorithms to ensure that conversations remain confidential and protected from unauthorized access. The STU III stands for Secure Terminal Unit, which highlights its primary function: to provide secure communication in various environments, including government and military settings.

This encryption capability is crucial for protecting sensitive information, especially in scenarios where eavesdropping or interception is a risk. The STU III employs digital encryption techniques, making it distinct from other types of communication devices which may not have inherent encryption capabilities.

While SATCOMs, radios, and telegraphs serve important roles in communication, they either do not focus primarily on voice encryption or don't incorporate the same level of sophisticated algorithmic encryption as the STU III. Some radio systems may support encrypted voice, but this does not encompass the specific secure terminal functionality that the STU III provides.