The ultimate code or ultimate override was a distress call signal in use in the United Federation of Planets that overrode all other communications and missions of a Starfleet starship, and required them to respond. The code was so highly classified that starship commanding officers were forbidden to submit an ultimate code to computer for decoding, rather commanders had to memorize a key which allowed them to decode the message into a coherent form. Nor could the starship commander keep a computer record of the code.