Explanation: The Global Maritime Distress and Safety System (GMDSS) is an international framework established by the International Maritime Organization (IMO) to enhance safety at sea for commercial vessels. It is specifically mandated under the Safety of Life at Sea (SOLAS) Convention. SOLAS requires GMDSS equipment on all ships of 300 gross tonnage or more engaged in international voyages. This ensures standardized communication protocols for distress, urgency, and safety information worldwide. Option A is too broad, as GMDSS is not required for *all* vessels, only specific commercial ones. Option C describes a practical benefit and scenario where GMDSS is vital, but not the regulatory trigger for its requirement. Option D refers to vessels explicitly *below* the tonnage threshold for GMDSS mandates.