That's a little disingenuous, regarding the F-15 -- there is the A/B series, with A being single-seat and B being the two-seat trainer, and the C/D series, with the same distinction between the two models. Both the F-15A and the F-15C are air superiority fighters, with an exclusively air-to-air role. The F-15E is a multirole fighter-bomber, not an air superiority fighter. The F-15X is an F-15E repurposed as a beyond visual range (BVR) missile truck, with data links to AEWC planes that can provide targeting solutions for those missiles. All of the letters between E and X have not been used.