In the mid-1950s, the US aeronautical engineers and designers were struggling with a seemingly insurmountable obstacle. That is, no matter how hard they tried, they could not get their latest fighter aircraft, the F-102 Delta Dagger, to break the sound barrier.
The shock waves encountered in the transonic realm proved too formidable…..until someone re-visited the theory of The Area Rule. That simply meant that the cross-section area of the aircraft had to progress smoothly from tip to tail, without abrupt changes.
In practice, it meant that the fuselage had to be “pinched” in to takr on a Coke-bottle shape – in order to compensate for the cross-section area of the wings.
Once they had “The Real Thing” designed in, everything went smoothly – the re-shaped F102 easily slipped past Mach 1,2 and they had a real fling from thence on.