Explanation: VHF Channel 16 is internationally designated as the primary frequency for distress, urgency, safety, and calling on maritime radio. This standardization ensures that any vessel in distress, or attempting to establish initial contact, can be heard by the widest possible audience, including the Coast Guard and other ships, which are required to monitor this channel. This dedicated frequency facilitates rapid communication during emergencies and provides a universal initial point of contact for non-emergency calls before shifting to a working channel. Channel 70 is reserved for Digital Selective Calling (DSC), which transmits automated distress alerts and routine call requests digitally. Channels 21A and 68 are common working channels; 21A is a Coast Guard working channel, while 68 is frequently used for ship-to-ship or ship-to-shore communications after initial contact on 16.