Which of the following is a required GMDSS function?

Correct Answer: Option A — Bridge-to-Bridge communications.

Bridge-to-bridge communications are a fundamental GMDSS functional requirement for safety of navigation. While weather facsimile may be useful, it is not a mandatory GMDSS functional requirement for all vessels. The primary focus of GMDSS is ensuring reliable distress alerting and essential safety-related communication between vessels and shore authorities.