The United States Air Force recently announced it would seek funding to procure a dozen new F-15X fighter jets as a part of its 2020 budget proposal, a move the branch was pushed toward by Pentagon officials, including the now-acting Defense Secretary and former Boeing executive, Patrick Shanahan.

Shanahan’s ties to Boeing, the company that produces F-15s, has been the subject of much speculation regarding the decision to buy new old jets, and media pundits have repeatedly questioned the need for a fourth-generation fighter as America continues to develop a fleet of fifth-generation aircraft. Even Air Force Secretary Heather Wilson has been quoted as saying the conflicts of the future will all require fifth-generation fighters, so what purpose would buying more fourth-gen aircraft possibly serve?

The thing is, there are actually quite a few arguments that can be made in the F-15X’s favor — most of which have been ignored by outlets that default to picking apart new initiatives as a means to produce conflict in their coverage. While purchasing the F-15X may not be a no-brainer, there are certainly some advantages to fielding a new batch of America’s old air superiority workhorse. It’s especially true regarding the media, and even Heather Wilson’s persistence in comparing the F-15 to America’s new show pony, the F-35.

The F-15X and F-35 would not serve in the same combat roles

The F-35 Joint Strike Fighter was built on compromise. While it is an extremely capable aircraft with potential far exceeding the combat operations it has participated in thus far, the “multi-role” part of the F-35’s design makes it a jack of all trades and a master of none. The F-35 was built to do a number of things with great effect, but in order to balance those mission requirements, the F-35 really isn’t the fighter America would want to lean on in a large-scale airborne conflict. While the F-35 is a capable long-range sniper, thanks to its advanced on-board sensor suite, air-to-air engagements are best left to the aircraft the U.S. Air Force employs specifically for that job: the F-22, and of course, the F-15.

Why would the Air Force want to buy new F-15s in the era of stealth fighters?
F-22s fly alongside an F-15 (USAF)

Take each aircraft‘s top speed, for instance. The F-35, which was built with more of an air-to-ground engagement strategy in mind, tops out at around Mach 1.6, or a bit under 1,230 miles per hour. The much older F-15’s top speed is better than 600 miles per hour faster. While the F-35 enjoys a stealth advantage, the F-15 was purpose-built to engage with enemy aircraft and is exceedingly good at it. That’s why the U.S. Air Force continues to maintain a sizable fleet of F-15s in the first place. There simply aren’t enough F-22 Raptors to go around and the F-35 wasn’t designed to do the same job.

America will be using F-15s for years to come anyway

Because the F-15X procurement plan would mean purchasing brand new F-15 air frames, the argument has sometimes been misrepresented as a decision to go back to employing fourth-generation fighters in situations that would otherwise fall to the F-35. That simply isn’t the case. With no set retirement date for the F-15 and years before the F-35 has been produced in sufficient numbers to eliminate America’s reliance on legacy air frames, the question isn’t between operating new F-15s or new F-35s — it’s really between operating new F-15s or old F-15s.

Why would the Air Force want to buy new F-15s in the era of stealth fighters?
F-15s in formation with an F-35 (USAF)

America’s existing F-15s have largely been in service for decades. Like any machine, as an aircraft ages, it becomes more expensive to keep operating at tip-top shape, and nearly two full decades of ongoing combat operations around the globe throughout budget issues and sequestrations has not done the F-15 any favors in terms of mileage or maintenance. A large part of the F-15X proposal is the understanding that operating costs would be reduced so dramatically, that the savings alone could pay for the new air frame procurement within a matter of years.

If Boeing’s cost estimates are reasonably accurate, that would mean the F-15X would simply absorb the F-15’s current role while offering reduced operational costs and improved combat capabilities.

The R&D has already been done

Although it’s been some time since the U.S. Air Force placed an order for F-15s, production of the fighter has continued throughout, along with the requisite systems upgrades one might expect from a fighter purchased in the 21st century. The F-15SA and F-15Q, exported to Saudi Arabia and Qatar respectively, have given Boeing the funding and justification to continue adding new innovations to the F-15 for decades. While America’s youngest F-15s may be more than 30 years old, the new F-15s flying in the Middle East come equipped with modern sensors, flight control systems, and avionics.

Why would the Air Force want to buy new F-15s in the era of stealth fighters?
The F-15SA shown in air-to-air configuration with eight AIM-120 AMRAAMs and eight AIM-9X Sidewinders, twice what America’s current F-15s can carry.

The F-15X, therefore, wouldn’t require the same sort of expensive updating one might expect if the Pentagon chose to bring an aircraft back from the dead. Repeated calls to restart F-22 production, an aircraft produced much more recently, have shown just how expensive it can be to bring an old program out of mothballs. The F-15’s cockpit, on the other hand, still has that new car smell because they really are new.

Not every operation needs an expensive stealth fighter

Last September, Air Force Secretary Heather Wilson said:

Hypersonic missiles may be why the Air Force wants 80 new F-15X fighters

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We are currently 80 percent fourth-gen aircraft and 20 percent fifth-generation aircraft. In any of the fights that we have been asked to plan for, more fifth-gen aircraft make a huge difference, and we think that getting to 50-50 means not buying new-fourth gen aircraft, it means continuing to increase the fifth-generation.”

At first glance, it’s hard to poke holes in that statement, but as you sift through older stories pertaining to the F-35, it starts to seem like it misrepresents not only the Air Force‘s overall combat strategy, but also the value of fifth-generation fighters.

Why would the Air Force want to buy new F-15s in the era of stealth fighters?
Not exactly fifth-generation tech. (USAF)

If it were true that all of the operations for which the Air Force is planning would benefit from or require the presence of fifth-generation fighters, it stands to reason that a pilot wouldn’t have died late last year testing a new light-attack aircraft that’s competing for an Air Force contract. Both of the aircraft that remain in the running for the contract look more like World War II-era fighters than anything else, and yet the Air Force is prepared to invest millions in the program for a simple reason: In some combat environments, you just don’t need an extremely expensive stealth fighter.

The F-35 is already so expensive to operate, the Air Force has suggested it may cut its overall order in half just to manage the cost. In non-contested airspace, like those found in many operations over Afghanistan and Syria, using an F-35 to conduct an airstrike against a Taliban drug warehouse is an awfully expensive way to blow up a shack. Fourth-generation aircraft like the F/A-18, F-15, and F-16 still have viable roles to play in combat operations that don’t need to sneak past anti-air assets.

The F-15X may not be the future of the Air Force, but it’s largely already in production, would save the taxpayer money, and would serve alongside the F-35 (instead of in its place) for years—or even decades—to come. If you want to take out surface-to-air assets in contested airspace, a fifth-generation fighter like the F-35 is just what the doctor ordered, but until the forthcoming PCA (Penetrating Counter Air) fighter enters into production, there’s plenty of room in America’s stable for battle-tested fourth-generation platforms like the F-15.