Rescue Aircraft sent ahead of single-engine jet fighters being delivered over ocean regions. The "Duckbutt" orbits along critical route segments, such as those for air refueling, and aids in rescuing flight crews, should a fighter need to ditch.
Movements of single engine fighters take place during repositioning to military exercise locations overseas, or the delivery of these planes from their overseas bases to repair depots. Bases on the Islands of Hawaii, Guam, and Okinawa are staffed with USAF Aircraft Delivery personnel. It is their job to coordinate with each agency which will service, repair, control, or Air Refuel the aircraft, making sure all of these operations run smoothly. One aspect of these efforts entails launching a "Duckbutt" aircraft (Usually an HC-130 "Hercules" four-engine turboprop) to provide rescue services for the crews if they ditch the plane.
The "Beeper" is a nickname for an "Emergency Locator Transmitter" (ELT) which transmits homing signals on UHF/VHF Emergency frequencies, guiding rescue aircraft and/or ground rescue personnel to an aircraft crash site, or parachute location.
All U.S. registered civil aircraft are required to be equipped with Emergency Locator Transmitters, which automatically activate when crash forces exceed 9 Gs, and transmit a homing signal that can be tracked by special receivers. Most military fixed-wing aircraft have these ELTs installed as well, with the exception of certain fighter aircraft.
Fighters may crash several miles from the point of crew ejection, so the parachute or seat frame containing the "Beeper" device is ideal for locating the crew, rather than the airframe. Large tanker and cargo aircraft may contain jettisonable ELTs which are released by the crew prior to a crash, and are called "Crash Position Indicators" (CPI).