Explanation: GMDSS (Global Maritime Distress and Safety System) survival craft radiotelephony equipment, such as a handheld VHF radio, is specifically required to operate on maritime distress frequencies. Channel 16 (Ch-16), operating at 156.8 MHz, is the international VHF distress, safety, and calling frequency for voice communication. This capability is essential for coordinating rescue efforts with ships and aircraft. Operation on 457.525 MHz is not a designated international maritime distress frequency for survival craft. Operation on 121.5 MHz is primarily an aeronautical distress frequency, historically used by ELTs (Emergency Locator Transmitters) and monitored by aircraft, but it is not the specified voice radiotelephony channel for GMDSS maritime survival craft. Therefore, only operation on Ch-16 meets the GMDSS requirement for survival craft radiotelephony.