Dated 15 July 1971, this page details the standardized visual signals fighter pilots used to communicate with one another when their radios failed - from the HEFOE system indicating hydraulic, electrical, fuel, oxygen, or engine emergencies, to hand signals for landing immediately, descending, or reporting fuel remaining. These wordless codes, essential for F-4 Phantom crews flying missions from Da Nang Air Base during the Vietnam War, ensured that a radio failure never meant a loss of critical communication in the air. Project: 218454