 They met with a French special forces commander in Paris from the 13th Parachute Dragoon Regiment, and spent a day aboard the USS "John Warner" (SSN-785), a nuclear powered "Virginia"-class attack submarine of the United States Navy.Both flew to Nellis Air Force Base where they spent two days at the USAF tactical fighter center for the US A-10 Thunderbolt II learning flight tactics, each night meeting the officers off duty in the "Hog-Trough", the squadron's famed bar.In addition, Greaney and Rawlings acknowledge over a dozen other personal, military service-members they contacted to gain information to write the novel.