F-15X vs.F-35: The Air Force Debate That Is Dominating the Headlines
In the end, the debate over choosing to buy F-15Xs or more F-35s is important but pales in comparison to much more consequential public debates that Congress and the Pentagon should be having. For instance, how will the Air Force achieve its 386-squadron goal for overall combat capability under the flat defense budgets proposed by the Trump administration?
If such cost comparisons are largely a wash, the achievable pace of replacement matters a great deal to the Air Force, which places foremost weight on the readiness implications of aircraft replacement. According to budget documents, F-15X deliveries would not match the possible numbers produced by the F-35 line. But the delivery of aircraft represents just one step in the process of standing up operational squadrons. One key fact the Pentagon only belatedly clarified is the exact timeline for the conversion of existing F-15C squadrons to either F-15X or F-35A squadrons.
Reading between the lines—given the nearly identical procurement costs and the uncertainty about long-term operating costs—Pentagon officials placed an extremely high value on how quickly on the transition timeline for F-15C replacement options. Officials, including Gen. Goldfein and Secretary Wilson, noted the transition from F-15C to F-15X would likely be very smooth. As Goldfein sums it up: “it allows you to use the same hangars, same construction, same base, same operating equipment which is 90 percent common, same maintainers, same operators and no time and minimal cost to make a transition.” In a May hearing, Air Force military procurement chief Lt. Gen. Arnie Bunch testified, “the time to transition from an F-15C to an F-15X we estimate at three to six months, while the time to transition from an F-15C to an F-35 could be anywhere from 18 to 36 months and would require MILCON and other attributes that are not in the budget.”
The fact that transitioning squadrons from the F-15C to the F-35A could take from one to three years effectively erases Lockheed’s ability to deliver 80 aircraft slightly more quickly. Of course, 18 to 36 months is a vast range. Using the lower bound of 18 months, the delay to transition from F-15Cs to F-35As might be matched by Boeing’s slower F-15X delivery timeline. At the higher bound of 36 months, the transition could be delayed by years, worsening the existing readiness problem created by aging F-15Cs and tilting the near-term analysis of operating costs in favor of the F-15X.
Capabilities and Missions
Coverage, commentary, and congressional questioning thus far has disproportionately focused on questions of capability—whether fourth-generation aircraft like F-15s are survivable in the high-end fight, the 2018 National Defense Strategy focuses on. Barrels of ink have been spilled over the past few months arguing about the degree to which future air warfare will require a mix of fourth- and fifth-generation aircraft, whether the F-15X’s payload capacity in comparison with the F-35’s makes it more attractive, and whether the ability to launch hypersonic attack weapons factored into the decision. In some cases, Air Force officials have actively engaged in these debates themselves, muddling the service’s own case.
The Pentagon and the Air Force did not give capability considerations as much weight in the analysis of F-15C replacement as the commentary would suggest. The gulf in capability between the F-15X and the F-35A is fairly obvious. As General Goldfein said, “The F-15 will never be the F-35,” though it’s not as if the F-15X is worthless, even in a contested environment. Still, numerous American Enterprise Institute analysts in recent years have extolled the virtues of the F-35A and called for drastically increasing the production rate both to meet mission objectives and to improve the health of the tactical fighter fleet. The transformational capability improvements of the Joint Strike Fighter are increasingly well-documented.
However, the mission of homeland air defense, which the F-15C replacement aircraft will perform, does not require a ton of eye-watering capability. As one defense official explained, this is a “mission set for which we do need the capabilities” of a tactical aircraft, “but for which we don’t need a penetrating aircraft that’s more expensive.” And, even if there were a major conflict with Russia or China, it’s not the case that F-35s involved in homeland defense could be just added to the front-line force. In such a scenario, it’s unlikely the defense secretary or the joint chiefs would recommend (and the president accept) the idea of stripping fighter squadrons from homeland defense to send abroad. In this respect, arguments over the comparative capability of the F-35A and F-15X somewhat miss the point.
Forest, Meet Trees: The Future of the Air Force
One way or another, the question of F-15C replacement will almost certainly be answered this year. Indeed, the pressure to purchase F-35As instead of F-15Cs appears overwhelming; the vast majority of interactions about this issue between Pentagon officials and Congress have evinced a high degree of skepticism about the decision. Ninety-nine House lawmakers signed a letterdemanding higher F-35 production, and dozens of members from both chambers have signed similar bipartisan letters. However, the Senate and House Armed Services Committees, along with the House Appropriations Committee, have all supported the F-15X buy, though each committee (and particularly HASC) has written scathing report language about the Air Force’s shoddy work on the program’s acquisition strategy and information flow to Congress.
The Air Force clearly and badly needs more F-35s. As General Goldfein recently bemoaned, “We should have 1,100 F-35s today. We have less than 300.” Meeting operational challenges in high-threat environments created by Russia and China will require a combination of F-35s, F-22s, and the F-22’s eventual air superiority replacement slated for fielding in the early 2030s. But the F-35A and F-15X should not be pitted against one another. The Air Force faces massive shortfalls in both the health and capability of its fighter fleet. Alongside the need for high-end capability, the Air Force simply needs more tactical aircraft immediately begin building a healthy force. As Air Combat Command chief Gen. Holmes mentioned, buying too few fighter aircraft per year means the Air Force will continue to pay ever-increasing amounts for smaller numbers of operational aircraft: “buying 48 F-35s a year will merely create a force, 30 years in the future, that averages 30 years of age per airplane.” General Goldfein has explained the exact same phenomenon: “[The F-15X buy] helps us to get at our target, which is 72 aircraft a year, which is what we need to be able to drive aircraft age from its current 28 average years to 15—which is what we think we can manage, by about a 2040 time frame. So the F-15C is about capacity; we're not taking a dime out of the F-35, nor would we, to buy F-15s, but we've got to fulfill this capacity shortfall with the F-15C.”
In the end, the debate over choosing to buy F-15Xs or more F-35s is important but pales in comparison to much more consequential public debates that Congress and the Pentagon should be having. For instance, how will the Air Force achieve its 386-squadron goal for overall combat capability under the flat defense budgets proposed by the Trump administration? Can the Air Force accelerate the development of a new sixth-generation aircraft capable of operating in the highest-threat areas of the future to maintain American air dominance? Why hasn’t the Pentagon asked for enough tactical aircraft to replace retiring airframes? Does the United States field sufficient airlift and cargo aircraft? What can be done to ensure a sufficient pipeline of pilots and maintainers in the future?
American sovereignty over the skies (and space) has ended in some areas, and it is coming to an end in others. The Pentagon and its overseers in Congress would profit from spending much more time on the hardest questions facing the Air Force. Picking either aircraft will not win or lose the next war; the comparative savings or delays are measured in low the billions of dollars over decades or mere months of readiness lost. But squandering an entire budget cycle debating F-15X or F-35 delays a necessary reckoning about the future of American airpower.
Rick Berger is a research fellow at the American Enterprise Institute (AEI), where he works on the defense budget, the National Defense Authorization Act, military appropriations and acquisition reform, as well as on other national security budget-related issues. Follow him: @bergerrichard.
This first appeared in RealClearDefense here.