Explanation: VHF Channel 70 (156.525 MHz) is designated exclusively for Digital Selective Calling (DSC). This dedication is crucial for the Global Maritime Distress and Safety System (GMDSS). DSC uses a specific digital format to send automated distress alerts, urgency, safety, and routine calls, providing a reliable and rapid method for initiating contact without continuous voice monitoring. A dedicated channel ensures these automated signals are not interfered with by voice traffic and are processed efficiently by radios, automatically alerting operators to important calls. In contrast, Channel 16 is the international *voice* distress and calling channel. Channels 21A and 68 are common working channels for voice communications, not for automated digital alerts.