The correct answer is B) An EPIRB transmitting on 406 MHz. An EPIRB (Emergency Position-Indicating Radio Beacon) is the primary source of transmitting locating signals in the GMDSS (Global Maritime Distress and Safety System) equipment. EPIRBs operate on the 406 MHz frequency, which is monitored globally by the COSPAS-SARSAT satellite system. When activated, an EPIRB will transmit a distress signal with the vessel's location, enabling search and rescue authorities to quickly locate and assist the vessel in distress. The other options are incorrect because: A) Survival Craft Transceivers are used for communication within the survival craft, not for transmitting locating signals; C) A SART (Search and Rescue Transponder) is used to indicate the location of a survival craft or distressed vessel, but it operates on a different frequency (9 GHz); and D) A Radio Direction Finder (RDF) is used to determine the direction of a radio signal, not for transmitting locating signals.