Explanation: Modern VHF radios equipped with Digital Selective Calling (DSC) feature a dedicated "Distress Hot Key." Pressing and holding this button immediately transmits an automated digital distress alert to all DSC-equipped stations within range. This alert includes the vessel's Maritime Mobile Service Identity (MMSI), current position, and time, significantly accelerating rescue efforts. It is the fastest and most reliable method to alert authorities and other vessels, even if the operator is injured or unable to speak. Option A, navigating menus, is too slow for an emergency. Option D, making a voice Mayday call first, bypasses the automated efficiency and guaranteed data transmission of DSC. While a voice Mayday call on Ch-16 is crucial for follow-up, the DSC alert should precede it to ensure the initial call for help is sent immediately. Option C is incorrect because the initial DSC alert is pre-programmed data; the nature of the distress is communicated via voice *after* the alert is sent.