The numbers are now official, and they are difficult to explain away. A Government Accountability Office report published on June 11, 2026 (GAO-26-108113) reveals that the F-35 Lightning II’s full mission capable rate has fallen to 25 percent. One in four aircraft can perform all assigned missions. The remaining three out of four cannot. The overall mission capable rate — the percentage of jets able to fly at least one type of mission — dropped to 44 percent. Both figures represent the lowest on record and continue a decline that has accelerated since fiscal year 2021. The Pentagon’s response is a $13.7 billion sustainment reset plan. Programme officials concede that readiness will get worse before it improves.

The Decline in Detail

The distinction between mission capable and full mission capable matters. A mission capable F-35 can fly and perform at least one type of sortie — perhaps air-to-air intercepts but not precision strike, or close air support but not suppression of enemy air defences. A full mission capable aircraft can execute every mission in its repertoire. For a platform that was designed from the outset to be an omnirole fighter — capable of air superiority, interdiction, close air support, electronic attack, and intelligence gathering simultaneously — a 25 percent FMC rate means three quarters of the fleet cannot do what the aircraft was built to do. The variant breakdown is revealing. The F-35A, operated by the Air Force, posted the highest FMC rate at 28.5 percent — still less than half the service’s 65 percent target. The F-35B (short takeoff and vertical landing, Marines) and F-35C (carrier variant, Navy) both registered approximately 14 percent FMC. These are the variants that operate in the most demanding environments: amphibious assault ships and aircraft carriers. That their readiness is roughly half that of the land-based A model reflects the additional corrosion, structural stress, and maintenance complexity of maritime operations.

What Is Driving the Decline

The GAO identifies multiple converging factors. Spare parts shortages top the list. Canopies are the single most common grounding item. A 2025 Lockheed Martin study found 48 parts that the supplier base cannot produce in sufficient quantities. The problem is structural: the F-35’s supply chain was designed for a smaller fleet. With more than 1,300 aircraft now delivered worldwide and over 800 in U.S. service, demand has outstripped the logistics architecture. Depot maintenance capacity is a second bottleneck. The programme historically underinvested in sustainment infrastructure, and the backlog at Tinker Air Force Base — the primary F135 engine depot — has grown steadily. Premature rotor blade coating distress has added unplanned engine removals to an already strained pipeline.

The TR-3 hardware and Block 4 software upgrade has compounded the problem. All 110 F-35s delivered in 2024 were an average of 238 days late due to TR-3 integration issues. These aircraft were delivered with interim software that limits them to basic training flights — they cannot fly combat missions. Block 4 completion, originally targeted for 2026, is now estimated no earlier than 2031. Lockheed Martin expects the full suite of technology upgrades to extend through 2032. Finally, there is the contractor dependence issue. The military lacks the technical data to independently maintain the F-35. Every major repair requires Lockheed Martin involvement, creating bottlenecks that a more open sustainment model might avoid. A “Warrior Right to Repair Act” is being pushed for the 2027 National Defense Authorization Act after similar provisions were stripped from the 2026 NDAA under industry lobbying.

The $13.7 Billion Reset

The Pentagon’s answer is the Global Support Solution Reset, launched in June 2025 by the F-35 Joint Program Office. The plan calls for $13.7 billion in additional funding through fiscal year 2031, distributed roughly as follows: $8 billion for the Air Force, $3.2 billion for the Navy, and $2.6 billion for the Marines. Of the total, approximately $7.3 billion is earmarked for depot-level spare parts and materials, $3.1 billion to expand depot capacity, and $3.3 billion for maintenance and fuel. The near-term requirement is $2.2 billion in FY2026–2027, with half of that going to spare parts. The target: an 80 percent mission capable rate and 65 percent full mission capable rate by 2030. Whether the money materialises is uncertain. The Air Force has indicated it can likely absorb its share. The Navy and Marine Corps have flagged “competing priorities” — a diplomatic way of saying that the F-35 sustainment bill is competing with shipbuilding, amphibious vehicle programmes, and every other unfunded requirement in the maritime services.

The Incentive Problem

Perhaps the most damaging finding in the GAO report concerns how Lockheed Martin was compensated for readiness performance. Between 2020 and 2023, the Joint Program Office paid Lockheed $114 million of approximately $269 million in available incentive fees tied to readiness improvements — during a period when readiness was declining. In 19 of 39 performance periods, the JPO and Lockheed adjusted full mission capable rates upward to qualify for higher payments. Without those adjustments, Lockheed would have earned roughly half as much. The JPO could not produce consistent records of these incentive payments, providing three different spreadsheet versions to auditors. The current contract, covering 2025 through 2028, contains no incentive fees tied to FMC rates at all. The GAO notes dryly that until the programme ensures “the future use of incentive fees better achieves the desired performance, JPO increases its risk of continuing to reward performance that does not help the program meet its goals.”

Context and Comparison

For perspective: the Air Force’s F-16C fleet — an aircraft that first flew in 1978 — maintains a mission capable rate of approximately 64 percent. The F-22 Raptor, the F-35’s older stablemate, sits at roughly 40 percent MC. The overall USAF fleet average hit 67 percent in 2024, the lowest in 20 years. The F-35’s 44 percent MC rate is better than the F-22 but substantially worse than the legacy fighters it is meant to replace. The programme’s lifetime sustainment cost for the United States alone is estimated at $1.6 trillion. Douglas Birkey of the Mitchell Institute offered a measured assessment: “The aircraft delivered in combat like none other. This proves the jet can deliver when the support is aligned.” He added: “I can’t emphasize how consequential underinvestment in readiness for many years was to the health of the F-35 and the entire aircraft inventory.” The GAO has made 46 recommendations on F-35 sustainment since 2014. As of March 2026, only 14 have been implemented. The remaining 32 are open. The F-35 is the most capable tactical fighter ever built. It is also, by the numbers, one of the least available. Sources: GAO Report GAO-26-108113 (June 11, 2026), Air & Space Forces Magazine, Breaking Defense, Military Times, Defense News, Stars and Stripes