Mark "Billy" Billingham spent 27 years in the military in the Parachute Regiment, with the Special Air Service (SAS) as a Mountie troop leader, sniper, and jungle warfare instructor. Since leaving the armed forces, he's worked as an A-list bodyguard to Angelina Jolie, Brad Pitt and Tom Cruise. He's now a consultant on Channel 4's "SAS: Who Dares Wins." We asked Billy to rate the realism of popular military scenes in movies, from "American Sniper" to "Commando" and "Black Hawk Down." Billy is the author of "The Hard Way: Adapt, Survive and Win."