A brevity call announcing the launch of an active radar-guided air-to-air missile (e.g., AIM-120 AMRAAM, R-77). These missiles employ their own onboard radar in the terminal phase, allowing the shooter to crank, notch, or recommit as needed.
Application in DCS World
“Fox 3” is critical in multiplayer BVR fights so all participants understand that an active weapon is in the air. This helps deconflict maneuvers and prevents multiple aircraft from unintentionally focusing the same target.