Rainbow Six By Tom Clancy

At its heart is ex-Navy SEAL John Clark, now the newly named head of Rainbow, an international task force dedicated to combating terrorism. In a trial by fire, Clark is confronted with a violent chain of seemingly separate international incidents. But there is no way to predict the real threat: a group of terrorists like none the world has ever encountered, a band of men and women so extreme that their success could literally mean the end of life on earth as we know it ... [goodreads]