second-in-command

In case of emergency, it means "save our souls". For example, if a boat is sinking and the people on the boat need help, they send out an SOS by radio or other signal to let rescuers know they need help. The people needing help can say "S.O.S" or send a signal/text/other form of communication with the letters and the rescuers immediately know that people are in trouble.

What is the context?