In attempting to analyze the role of luck in war, a rather narrow definition of luck is necessary. The conventional dictionary definitions of luck are "a force that brings good fortune or adversity" and "the events or circumstances that operate for or against an individual." Those definitions are so broad that they would appear to cover many, perhaps most, events in war. There is in literature an old expression, deus ex machina, a translation into Latin of the original Greek th os ek mechan s. While it literally translates as "a god from a machine," its meaning is a person or thing that appears or is introduced suddenly and unexpectedly and provides a contrived solution to an apparently insoluble difficulty. In the book a similar but probably unique concept, felix ex machina, will be used to denote certain extreme instances of luck which was relatively sudden, completely unexpected with dramatic consequences, good or bad, in war.Greer, Gordon B. is the author of 'The Role of Luck', published 2007 under ISBN 9780595447961 and ISBN 0595447961.