What is the area rule and how does it reduce transonic drag?

The area rule (Whitcomb area rule) states that transonic wave drag depends primarily on the longitudinal distribution of cross-sectional area, not the specific shape. For minimum wave drag, the total cross-sectional area should vary smoothly along the aircraft length, ideally following a Sears-Haack body distribution. This led to the 'Coke bottle' fuselage indentation near wings. Application reduces transonic drag rise by 25-30%. Modern aircraft like F-106 and Convair 880 incorporated area ruling, and it remains important in any transonic design.