The Air Force Has the F-35. So Why Is It Still Buying New F-15s?

On September 29th, the Air Force ordered 22 more F-15EX fighters from Boeing. The F-15EX is the latest version of the F-15, a fighter that first flew in 1972. It isn't stealthy, and the Air Force already flies a stealth fighter, the F-35, which it's still buying. Even so, this spring the Air Force more than doubled the number of F-15EXs it plans to buy, from 129 to 267. So why does an Air Force that has the F-35 keep buying new F-15s? Kadena Air Base, on the Japanese island of Okinawa, is the Air Force's closest land base to Taiwan. F-15 Eagles had flown from there since 1979. By 2022, those Eagles were badly worn out. The Air Force had already limited how hard they could maneuver and how fast they could fly. That fall, it announced that all 48 would go home over the next two years, with no permanent replacement picked out. Other fighters came in on temporary deployments, starting with F-22s from Alaska, and the base has relied on rotations like that ever since. The Air Force had a stealth fighter in full production. But when General Kenneth Wilsbach, who led Pacific Air Forces at the time, talked about a permanent replacement, he named the F-15EX. He wanted it for air superiority, and for the long-range weapons it can carry. In 2024, that became the plan. 36 F-15EXs for Kadena. So, for one of its most important bases in the Pacific, the Air Force picked a fighter whose basic design goes back to the 1970s. The F-15EX is old, mostly on the outside. Its flight controls, its radar, and its electronic warfare system are all new. And that last one warns the crew about enemy radars and can jam them. The outline is what new hardware can't change. The F-15 was designed before stealth aircraft existed. Its shape, and the weapons hanging under its wings, bounce a lot of radar energy back. The F-35 was designed to cut that down. Its carefully aligned edges, its reduced engine signature, and its internal weapons bays all shrink its radar signature. Enemy radars have a harder time finding and tracking it. It isn't invisible, but in heavily defended airspace, Being harder to track buys time and room to work. That design has a cost. To stay as hard to track as possible, an F-35 carries its weapons inside its body, in two internal bays. That limits how many it can bring on one flight, and weapons were exactly what Wilsbach wanted the Kadena jets to carry. The F-15EX goes the other way. Older F-15s carried eight air-to-air missiles. The EX's additional missile stations bring that capacity to 12. Missiles were first fired from those new stations during testing over the Gulf of Mexico in 2022. It can also carry big weapons that won't fit inside a stealth jet. When the Air Force presented its budget this April, it pointed to exactly that — how many weapons the F-15EX carries and its role in the Pacific. It also links the jet to defending the U.S. against cruise missiles. A fighter chasing a cruise missile off the American coast isn't flying into enemy air defenses. Out there, getting airborne with plenty of missiles matters more than being hard to track. The two jets have already trained in the same force. At Northern Edge, a large exercise in Alaska in 2021, the F-15EX worked alongside the F-35. Some analysts picture a bigger war divided between them. With stealth jets closest to the heaviest defenses, and F-15EXs firing long-range weapons from farther back. That's an idea, not a tested plan. The exercise showed the jets can operate together, not how a war would split the work. There's a catch, though. When stealth isn't needed, the F-35 can hang weapons under its wings, too. On a homeland defense mission, an F-35 could load up as well. If more missiles were all the Air Force needed, more F-35s could supply plenty of them. The first operational unit to receive the F-15EX is in Portland, Oregon. The Oregon Air National Guard's 142nd Wing had been flying F-15Cs, and in 2024, it started trading them for the new jet. From Portland, the wing keeps fighters on alert around the clock for NORAD, covering the Pacific Northwest from Northern California up into British Columbia. A fighter unit is built around its airplane—the hangars, the tools, the spare parts, the maintainers who know the jet. In Portland, all of that was already set up for the F-15. The new jets moved into the existing facilities, without the tens of millions of dollars in base upgrades that F-35s have needed. The switch still took work. The wing's commander said about 70% of the parts are shared with older F-15s, but his maintainers had to learn what he called a whole new system. That's a much smaller jump than turning an Eagle unit into an F-35 unit. Kadena is on the same path. Its 67th Fighter Squadron used to fly F-15Cs, and it's set to become the base's first F-15EX squadron. Test jets have already flown in twice, the second time to check maintenance and logistics before the permanent jets arrive. Those permanent jets are late. A strike at Boeing's St. Louis plant stopped production for months in 2025. The first jet painted for Kadena left the factory in August, and arrivals are now expected this fiscal year instead of this past spring. The bigger target follows the same pattern. The Air Force says the extra jets will first finish equipping units that are already switching. Then, they'll start replacing the F-15E Strike Eagle, the two-seat strike version of the F-15. Its 2027 budget also proposes retiring 20 of the oldest Strike Eagles, while it keeps buying F-35As. So, the jump to 267 is about replacing aging F-15s. It doesn't mean the Air Force's whole fighter force is doubling. Moving into existing bases saves construction and some retraining. That makes it tempting to assume the jet itself is cheaper, too. And early on, Boeing pitched it that way. The latest numbers don't settle that. This order works out to about $108 million per F-15EX, before the engines, which the Air Force buys separately. The F-35 program puts its latest F-35As at about $92 million on average, engine included. Those figures cover different things, and the Air Force has said the two programs don't line up for a direct comparison. What they don't show is a clear discount on the F-15EX itself. Its supporters point to conversion and long-term operating costs instead, but those are estimates, and they vary depending on who's counting. So, back to those 22 jets. The F-35 is built to be hard to track where defenses are thickest, and it keeps its weapons inside to do that. The F-15EX makes the opposite trade. It can carry up to 12 air-to-air missiles. It can also carry big weapons a stealth jet can't fit inside. And it slots into units like Portland and Kadena that already know how to keep an Eagle flying. The Air Force wants both kinds of jet. And for the squadrons that have to replace their old Eagles, the F-15EX is the one they can take on without starting over. If you'd like more on why the military buys what it buys, subscribe.