On July 29, 1972 Air Force F-4s and North Vietnamese MiG-21s engaged fifty miles northeast of Hanoi. The F-4s shot down two MiGs, and the MiGs shot down an F-4 whose callsign was Trigger 4 (the fourth F-4 in a flight of four). Such is the historical record, but some pilots thought the record was wrong. They suspected that only one MiG fell, and that the second kill was really Trigger 4, a victim of fratricide perpetrated by Cadillac 1, the lead F-4 of another flight of four on a MiG sweep out of Udorn, Thailand. Fortunately, the two-man crew of Trigger 4 survived the shootdown and several months of imprisonment in Hanoi.In the mid-1990's, an Air Force Reserve colonel conducted research on Trigger 4's loss. His skill and persistence permitted him to gather an impressive body of data on this one engagement. He reached a preliminary conclusion that it was "highly probable" Trigger 4 had been a victim of fratricide. Yet, he knew his conclusion was based on circumstantial evidence; he had no smoking gun. In 2000, the pilot of Trigger 4, who was aware of the Air University researcher's findings, wrote to the Air Force Chief of Staff and asked that the matter be investigated fully. In response the Chief of Staff directed a team of experts to reconstruct the air battle of July 29, 1972 to determine the facts surrounding Trigger 4's shootdown. He also appointed a non-partisan senior mentor to monitor the team's thoroughness and methodology.The Project Trigger team began work in the Checkmate division of the operations directorate. They built upon the foundation provided by the Air University researcher. Even though this air-to-air battle occurred nearly 29 years ago, the team found and interviewed 27 participants and other interested observers of the battle. The team was fortunate to be able to synchronize five cockpit tapes, including three from the F-4 flight leaders in the battle, and two others from the flight whose kill was in question. Using the tapes, eyewitness accounts, intelligence records, and the team's considerable experience, they reconstructed theengagement, and determined that a MiG-21 shot down Trigger 4.As the reader sees the story unfold, it becomes clear that there are important lessons. None of the three aircrews shot down in this engagement realized they were under attack until it was too late. But firing beyond visual range is also risky, and the system of rules in place today is the direct result of experiences from air battles such as this one. A culture of discipline in the Air Force is animportant part of what makes it the best in the world. "Get the first shot" may be axiomatic, but identifying the target is even more basic.