US Air Force/Ethan Wagner In March, the Air Force accepted the first F-15EX, the first new fourth-generation fighter in 20 years. The F-15EX is based on a proven design and will replace jets that are close to their breaking points. But critics say that in the wars of the future, a jet like the F-15EX is just "an expensive target." In March, the Air Force accepted its newest fighter, the F-15EX, the first new fourth-generation fighter in over two decades. At a ceremony to mark the occasion, Air National Guard Director Lt. Gen. Mike Loh said the fighter's arrival "is very timely," as the Air Force "must ensure that we have the most capable combat aircraft defending our shores during this time of great-power competition."