On July 25, 1969, 22-year-old Army Specialist John Fogle, an OH-6A crew chief, was torn open by AK-47 rounds — after the observation helicopter on which he was manning an M-60 machine gun unexpectedly flew low over a North Vietnamese Army encampment. One round severed his femoral artery. As John used a bungee cord to create his own tourniquet, the helicopter’s pilot guided the shot-up bird to a field medical post in Phu Bai, fortunately only about 10 minutes away. At the 22nd Field Hospital, surgeons applied lessons they had learned as part of an ongoing study of the best ways to repair injured blood vessels. Their efforts, and those of others who operated on John over many months to come, would ensure he didn’t lose his right leg. Waking from that first surgery in Phu Bai, John promised doctors he would keep in touch, sending details of his recovery. Listen to the story of how the recent digitization of the Vietnam Vascular Registry helped him — nearly a half century later — keep that promise, and say thanks. Here’s how I told the story for CBS Eye on Veterans.