Final answer:
US civil and military aircraft must be equipped with automatic-type ELTs, essential for search and rescue in the event of a crash.
Step-by-step explanation:
US registered civil and military aircraft are required to have an automatic-type Emergency Locator Transmitter (ELT) attached to the aircraft. With some exceptions, federal aviation regulations require that these aircraft be equipped with ELTs that are set to activate automatically in the event of a crash to help facilitate search and rescue operations. These devices transmit a distress signal that can be detected by satellites and ground stations, which is crucial for locating downed aircraft.