Mayday is an emergency procedure word used throughout the fire service and also internationally as a distress signal in voice procedure radio communications. It derives from the French "venez m'aider", meaning "come help me".
http://en.wikipedia.org/wiki/Mayday
Also used in military - Navy expressions example:
http://www.navy.mil/navydata/traditions/html/navyterm.html#head
http://en.wikipedia.org/wiki/Mayday
Also used in military - Navy expressions example:
http://www.navy.mil/navydata/traditions/html/navyterm.html#head