What's Behind a Number?
Boeing launched the jet age in 1958 with the first commercial flight of the legendary 707. That model was followed by the 727 in 1964, the 737 in 1968 and the 747 in 1969. Following that sequential evolution, the 717 should date to the early 1960s rather than the late 1990s. However, Boeing intentionally skipped over the 717 designation when it launched the 727 and other jetliners in the mid-1960s.
The 717 moniker was reserved for a military derivative of the 707. Indeed, the KC/C-135 series of tanker-transport/cargo airplanes was initially designated as the 717. In January 1998, the model number was officially reassigned to Boeing's commercial division for its regional jetliner. The "1" symbolizes the fact that the 717 is a 100-seat airplane.