http://en.wikipedia.org/wiki/MEDUSA_%28weapon%29 .

MEDUSA is also a fictional energy weapon in Philip Reeve's novel Mortal Engines, completely different from the real-life MEDUSA weapon and its name is not known to be an acronym.

Turns out it is not completely different to the real life weapon, turns out it's exactly the same thing:

http://www.wired.com/2007/08/the-other-medus/