The US Government Accountability Office has been monitoring the US F-35 programme since 2014. In its latest report it looks at sustainability and aircraft availability across the US fleet. The results are not good but the report also shines a spotlight on some wider air power issues and more generally, the future of expensive and sophisticated manned platforms.
Whisper it quietly but air power is undergoing radical change. The long-held view that conventional air power provides a flexible, versatile, persistent and concentrated method of delivering kinetic effect is now being challenged. Wars in Ukraine and the Gulf have shown that armed forces do not necessarily need expensive manned platforms to strike their enemies or undertake intelligence, surveillance, and reconnaissance (ISR) missions. Ballistic missiles and unmanned aerial vehicles (UAVs) have served Iran, Ukraine and Russia well and have the added benefit of being cheaper and quicker to develop as well as possessing lower sustainment costs when compared to manned aircraft.
The cost of modern manned platforms has been put under the spotlight yet again with the publication of the US Government Accountability Office’s (GAO) report, F-35 Sustainment – Actions Needed to Ensure Updated Strategy Improves Persistent Readiness Challenges. In terms of sales, the multirole F-35 Lightning II has been an outstanding success. With around 1,330 in-service or on order with 20 air arms around the world, the majority of these, approximately 800, are currently operated by the US Air Force, Navy and Marines. The US plans to add another 1,700 F-35s by the mid-2040s. In total, this current global combined fleet has amassed over one million flight hours.
In terms of context, the F-35 is provided in three variants: the F-35A is a conventional take-off and landing (CTOL) aircraft; the F-35B is the short take-off and vertical landing (STOVL) variant while the F-35C is designed for operation from carriers, with catapult-assisted take-off and barrier-arrested recovery (CATOBAR). According to prime contractor Lockheed Martin, the fly-away costs of these platforms are USD 82.5 million, USD 109 million and USD 102.5 million respectively.
Few would argue that the F-35 is a technologically complex aircraft that is highly capable but as we have seen, that capability comes at a price, or perhaps that should be two prices; initial procurement cost and then longer term sustainment costs. According to a June 2025 report by the US Congressional Budget Office (CBO), operational support costs for the Department of Defence’s (DoD’s) F-35 fleet in 2023 was USD 5 billion. This cost comprises fuel, maintenance and personnel.
Longer term, the most recent GAO report states that, “The F-35 Lightning II aircraft is the Department of Defense’s most costly weapon system, with sustainment costs for the United States estimated at USD 1.6 trillion for the life of the program to 2088.” Given the DoD’s record of underestimating sustainment costs in the past, that figure will only increase.
It is not just the US that is suffering from higher than expected sustainment costs. A UK National Audit Office (NAO) report into the UK’s F-35 capability from July 2025 stated that the programme’s “whole-life costs were considerably higher than the Ministry of Defence has publicly reported”. The NAO estimates are based on 138 aircraft with an out-of-service date of 2069, although this figure does not cover fuel, personnel and infrastructure costs.
The rapid evolution of technology can also cause problems as prime contractor Lockheed Martin, along with partners Northrop Grumman and BAE Systems, strive to maintain the aircraft’s cutting edge lead over potential adversaries. There has been significant technological changes and doctrinal air power shifts since Lockheed Martin won the Joint Strike Fighter (JSF) programme in 2001 with its X-35 proposal before the F-35 undertook its maiden flight in 2006 and then entered service with the US Marine Corps in 2015.
As an aside, it is worth reflecting that the F-35 Lightning II drew its name from, the Lockheed P-38 Lightning that first flew in January 1939 and entered service in July 1941. A total of 10,037 P-38s were built. Although clearly not a direct comparison with the F-35, the juxtaposition of both types does highlight the increase in the time taken to develop a modern combat aircraft and the complexity and costs involved. That trend will continue with platforms such as the Boeing F-47 and poses the question of affordability.
Chasing technology to achieve perfection is challenging. In 2024 for example, the US DOD was managing “a [USD] 16.5 billion modernization effort” designed to “provide the F-35 with new capabilities through both hardware and software upgrades.” These included “radar enhancements, weapons, and technology to avoid aircraft collisions. Some of these capabilities depend on technology updates that were planned for delivery last July [2023] but they are delayed because of software stability issues.”
This so-called Block 4 upgrade is also notable for the fact it was initially forecast to cost USD 10.6 billion and has now increased to USD 16.5 billion and has now been delayed. This provides yet another example of how costly manned platforms have become and the inability of governments and the military to manage their costs.
The other technology challenge that was recently highlighted by Warsight concerns inter-fleet compatibility. Jon Lake wrote that the UK’s current F-35 fleet “is handicapped by encompassing aircraft with different configurations and different software standards. Markedly poor availability further complicates the situation.” This situation creates problems on a number of levels. As well as discrete maintenance demands for individual aircraft, concerns surround whether aircraft will be able to operate together at the operational level?
According to the Washington DC-based F-35 Joint Program Office (JPO) Lake’s findings are echoed by the US services in that there is “high technical complexity due to continuous development” of the aircraft. “There are multiple configurations of the F-35 in service today, each requiring different maintenance practices and parts supply requirements.”
In basic terms, the US GAO has found that since 2021, F-35 sustainment costs have continued to rise while readiness has declined. In other words, the DoD are paying more for less air power capability. The GAO uses two metrics to define availability. The Mission Capable Rate (MC) shows the “percentage of time the aircraft can perform one of its tasked missions.”
The second benchmark is the Full Mission Capable Rate (FMC) and this is defined as the “time the aircraft can perform all of its missions.” Between 2021 and 2025, the MC declined from 67% to 44% and the FMC from 38% to 25%.
Unfortunately, clouds remain on the horizon as the GAO has reported the JPO as saying sustainment performance will likely get worse before it gets better. Initial improvements are not expected before the end of this year “or later.”
In addressing this failure to meet performance and readiness goals, the F-35 JPO has updated its sustainment strategy. Known as the Global Support Solution (GSS) Reset, this initiative calls for an additional USD 13.7 billion through FY31 but is simply throwing money at the problem going to solve it?
Rather pointedly, the GAO states that since 2014, “we have examined various aspects of the F-35 program and have made 46 recommendations designed to improve the department’s operations and sustainment of the program…as of March 2026…[only] 14 had been implemented…but the DOD has not taken action to implement the other 32.” And here perhaps, is the nub of the sustainment issue. Instead of throwing money at the problem the DOD, JPO and contractors need to undertake radical, manifold and meaningful logistical reforms.
Areas ripe for reform are highlighted in the GAO report. Perhaps the most important is a lack of spare parts at home bases and deployed locations around the world that prevent aircraft being rapidly returned to service. This issue is compounded by the “inadequate training” of maintenance personnel and a lack of maintenance support equipment on the flightline. More surprising, especially given the one million flight hours accrued by the F-35 across the world, the GAO states that there is a “lack of access to technical data for repairs [that] delays the maintenance process at the organizational and depot levels.”
The GAO also holds the depot level maintenance efforts to account saying that there is too much emphasis on contractors and that the DOD’s “decision-making ability and influence” over the contractors is “limited”.
In 2024 the JPO conducted an evaluation of its F-35 sustainment strategy where it recognised the lack of spares and consumables issue. It highlighted that historically, spares holdings were underestimated and that many were only being ordered after they had run out of stock. They also highlighted that aircraft inspections were being conducted sequentially and if some were done together it would increase aircraft availability.
The JPO’s GSS Reset initiative that was announced in June 2025 emphasises seven initiatives, four reflecting supply and three dedicated to maintenance. In simple terms, the supply side of the equation features improved spare parts modelling to predict requirements and investment in spares holdings while the maintenance side sees the adoption of concurrent maintenance tasks and inspections, the standardisation of staffing levels and adopting new maintenance tools and enhancing best practices.
Another key method that the DOD is seeking to improve readiness is by adopting a Working Capital Fund (WCF) to increase spares holdings. The GAO says that, when a WCF is used to finance “inventories of supplies it can provide some benefits to more effectively control and account for the cost of a program.” The feeling in Washington is that the F-35 programme is simply too large to be managed by annual appropriations. According to the GAO, the transition to a WCF “will take place no earlier than October 2028.”
Although commendable that the DOD is using GSS Reset and establishing a WCF to procure spares, some of the failings of the current system are staggeringly unprofessional. For example, the GAO says that the DOD cannot “fully account for F-35 spare parts within the supply chain” and does not know the exact location of these parts. In addition, “DOD does not have comprehensive cost information for individual F-35 spare parts.” Other failings that have been identified include a lack of discrete part numbers allocated to a correlated F-35 spares database and an IT system that is incapable of managing those parts.
On one hand it is surprising that following a 58 page report, the GAO only makes three recommendations. However since 2014, the GAO has made 46 recommendations concerning the F-35 programme in its various reports and as of March 2026 the DOD had only implemented 14 of them, leaving 32 fallow.
Its first recommendation is for the F-35 Program Executive Officer (PEO) to develop risk mitigation plans to encompass areas such as industry capacity, affordability “and alignment with service goals” in line with sustainment improvement initiatives such as GSS Reset.
The second recommendation concerns the current use of industry incentives that need to be better managed and the adoption “of penalties for poor performance…or omitting performance incentives” altogether. The hidden message here as that the DOD and industry must work together and cooperate more.
Finally, and allied to the second recommendation, the GAO suggests the Under Secretary of Defense for Acquisition and Sustainment in consultation with the F-35 PEO, generates an “incentive fee metric and payment information” and create a procedure for documenting contractual changes.
Modern fifth generation combat aircraft are eye-wateringly expensive and sixth generation platforms even more so. The real challenge centres on sustainment and the need to generate high levels of serviceability and therefore, availability. Having 25% of a nation’s fleet at full mission capability is unacceptable. In a high-intensity conflict that figure would be even lower due to aircraft losses both in the air and due to poor force protection measures on the ground.
Such sophisticated platforms are also continually being upgraded with new hardware and software and these enhancements take time, again having a detrimental effect on platform availability. As the F-35 Block 4 upgrade highlights, they are also expensive and this ‘technology on the go’ is difficult to predict and nearly impossible to cost.
This raises the question of replacing highly sophisticated manned platforms with other options. That could be by adding Collaborative Combat Aircraft (CCA) or making greater use of ballistic and long-range strike missiles as well as UAVs. The issue here is that CCAs require a ‘mother ship’ to control them and so once again, sustainment and availability come to the fore.
Many air forces around the world are looking at their budgets and asking just what they can afford. The chances are fewer will be opting for an all-manned air power solution in the future.
