Sierra Six - Mark Greaney

In his research for the Gray Man novels, Mark Greaney has traveled to more than thirty-five countries and trained alongside military and law enforcement in the use of firearms, battlefield medicine, and close-range combative tactics. He is also the author of the New York Times bestsellers Tom Clancy Support and Defend , Tom Clancy Full Force and Effect , Tom Clancy Commander in Chief , and Tom Clancy True Faith and Allegiance . With Tom Clancy, he coauthored Locked On , Threat Vector , and Command Authority .