Final answer:
The communications equipment described is a Secure Telephone Unit (STU or STU-III), which includes a dial pad, is battery-powered, used with the SB-3614 switchboard, and allows for secure station-to-station calls.
Step-by-step explanation:
The piece of communications equipment described in the question is likely a Secure Telephone Unit, commonly known as a STU or STU-III. These devices typically have a dial pad, are battery powered, and can be used with the SB-3614 switchboard in secure communications setups. STUs allow for encrypted station-to-station calls, ensuring that sensitive information is protected during transmission. Most commonly used by government and military entities, these pieces of equipment are essential for maintaining secure lines of communication.