Which of the following describes a Group MMSI?

A Group MMSI (Maritime Mobile Service Identity) is specifically designed to communicate with multiple vessels at once, making it ideal for coordinating with a defined group of ships. The primary purpose of a Group MMSI is to facilitate group calls rather than targeting individual ships, which aligns perfectly with the function described in the correct answer.

Group MMSIs are particularly useful in scenarios such as search and rescue operations or during coordinated maritime activities where many vessels operate closely together and need to maintain communication with each other. This unique capability enhances operational efficiency and situational awareness for all ships within the group.

The other statements do not accurately describe the characteristics of a Group MMSI. For instance, it does not always start with three zeros, nor is it limited to a specific vessel; instead, it can encompass multiple vessels under a shared communication channel. Additionally, while MMSI numbers can vary in length depending on their type, a Group MMSI is not strictly defined to be a 7-digit number. The primary takeaway is that the Group MMSI facilitates broad communication among a defined set of vessels, which is key to its function in maritime operations.