VHF emergency civilian 121.5 mHz R/T
UHF emergency military 243.0 mHz R/T
MF emergency frequency 500 kHz. (it is in "the book", no idea how is used)
HF emergency frequency 2,182 kHz AM or USB R/T
UHF emergency beacons 121.5, 243 and 406 mHz.
xxx
Of interest to you - merchant marine vessels, at high seas, monitor -
HF general call frequency ship-to-ship 4,125 kHz USB (night)
HF general call frequency ship-to-ship 8,291 kHz USB (day or night)
HF general call frequency ship-to-ship 16,590 kHz USB (day)
Most ships have D/F capability on these. Can give your QDR...
xxx
Happy contrails
P.S. I was an active "radio ham" in the old days...
When bored on oceanic flights, sometimes played with these HF freqs...