Mark Greaney is the co-author of three Number One Sunday Times bestellers with Tom Clancy: Locked On, Threat Vector and C ommand Authority. In his research for these novels, Greaney travelled to seven countries and trained alongside military and law enforcement in the use of firearms, battlefield medicine and close-range combat tactics. He now writes for the Tom Clancy series of novels alongside Grant Blackwood. He lives in Memphis, Tennessee.