Explanation: The Digital Selective Calling (DSC) controller is the dedicated equipment for initiating digital distress alerts and calls to individual stations or groups. DSC is a component of the Global Maritime Distress and Safety System (GMDSS), allowing vessels to transmit pre-formatted digital messages over VHF, MF, or HF radio. Users program the DSC controller with their Maritime Mobile Service Identity (MMSI) and can trigger a distress alert or send a direct call to another station by entering their MMSI. NAVTEX (A) is a receiver for broadcasting maritime safety information, not a transmitter. GPS (B) provides positioning data, which can be *fed into* a DSC controller, but it does not initiate radio transmissions itself. A Scanning Watch Receiver (D) is designed to listen to multiple frequencies, not to transmit or initiate calls.