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Sustainment Constrains Operational Readiness

Availability is shaped by interconnected constraints. Spare parts are unavailable or delayed. Depot-level component repair takes too long. Technical data are not available to maintenance organisations with sufficient depth or speed. Software problems, limited supplier capacity and contractor dependence add further pressure across the fleet.

The Joint Program Office plans additional procurement of parts and material worth more than USD 7 billion through 2031. The requirement indicates that the existing supply system has not kept pace with fleet growth, ageing and operational demand. Even low-volume components can ground otherwise serviceable aircraft when replacement parts or repair capacity are unavailable.

Depot maintenance is a further bottleneck. F-35 sustainment relies on manufacturers, military depots, suppliers, warehouses and transport networks. Delays in any part of this system directly reduce squadron and unit availability. Cannibalisation can make individual aircraft available in the short term, but reduces readiness elsewhere in the fleet.

Contractor dependence affects diagnostic data, technical support, supply-chain management and parts of airframe and engine maintenance. In deployed or contested environments, this structure can delay fault isolation, repair authorisation and component replacement. Military maintenance autonomy therefore remains limited.

Under these conditions, higher production output does not automatically create more available combat power. Each additional aircraft increases demand for spare parts, depot throughput, qualified personnel, software support and technical-data access.

TR-3 and Block 4 Constrain Operational Readiness

Technology Refresh 3 remains a major limiting factor. Its hardware and software architecture is intended to provide additional processing power for elements of the Block 4 programme. Delays in software maturity, integration and retrofit activity directly affect aircraft acceptance and operational readiness.

The United States accepted TR-3 aircraft before the software baseline had matured for full combat employment. This reduced the number of completed aircraft held by industry. It also transferred integration and retrofit requirements into operational units. The aircraft can support selected training tasks, but they consume maintenance capacity and require further work before entering the fully operational combat inventory.

Training, retrofit activity, fleet maintenance and deployment preparation are therefore competing for the same technicians, facilities and aircraft. Delayed mission software, sensor integration and improvements to power and cooling extend the period between delivery and full operational availability.

Block 4 is already affecting current readiness. Its delays constrain the conversion of newly delivered aircraft into deployable and fully mission-capable units.

Radarless F-35B Deliveries Extend Concurrency Risk

Six U.S. Marine Corps F-35B aircraft were accepted without AN/APG-85 radars. The aircraft were delivered with ballast in the radar bay because delivery of the new radar has been delayed.

The earlier AN/APG-81 cannot be installed as an interim solution. The affected aircraft are structurally configured for the AN/APG-85 and will require retrofit at a later stage.

Without their primary radar, the aircraft can support basic flight training. They lack critical functions for combat training and operational employment, including air-picture generation, target search, target tracking, air-to-ground targeting and radar-supported weapons employment.

The significance lies not in the number of six aircraft, but in the nature of the delay. Earlier concurrency issues primarily affected immature software, delayed mission functions and retrofit workloads. Radarless F-35B deliveries now extend concurrency into a core sensor of the combat system.

Further deliveries without AN/APG-85 radars would increase retrofit demand, training shortfalls and maintenance pressure in receiving units. The Air Force and Navy could face comparable deliveries later in 2026 if radar production does not proceed as planned.

The USD 13.7 Billion Reset

The Joint Program Office launched the Global Support Solution Reset in 2025. It has set programme targets of an 80-percent mission capable rate and a 65-percent full mission capable rate by 2030. According to the GAO, these are programme objectives whose achievement depends on several conditions that have not yet been secured. The plan requires an estimated additional USD 13.7 billion through 2031.

The funding is intended to improve spare-parts supply, repair capacity, maintenance throughput, supply-chain management and sustainment structures. The scale of the requirement shows that previous assumptions about fleet size, ageing and operational intensity were insufficient.

The targets require suppliers to deliver more components, repair facilities to increase throughput, depots to reduce turnaround times, and contractors to provide technical data and support faster. These conditions depend on industrial capacity, repair capacity and data access. Budget authority alone cannot generate those capabilities.

The GAO identifies limited industrial capacity, critical-parts shortages, insufficient technical-data access and immature mitigation measures. Fleet-wide recovery to 80 percent mission capable and 65 percent full mission capable has therefore not been supported by demonstrated industrial output or an executable risk-mitigation framework.

Any availability gains will depend on whether spare parts, repair capacity and technical support can be prioritised against the most urgent operational requirements. The reset can reduce the current deficit. Its 2030 targets are not yet credible under currently visible industrial conditions.

Implications for U.S. Defence Capability

Low availability reduces the United States’ ability to employ fully mission-capable F-35 units across several theatres at the same time. The F-35 is assigned tasks in air defence, air superiority, precision strike, ISR, targeting and networked air operations.

Low full mission capable rates increase the resources required to generate a given number of fully operational sorties. The services must commit larger fleet shares, more personnel, greater spare-parts holdings and additional maintenance reserves. This reduces available capacity for rotation, regeneration, training and rapid reinforcement.

U.S. defence planning therefore faces increased prioritisation pressure between Europe, the Indo-Pacific, the Middle East and homeland defence. Available aircraft, spare parts, depot capacity and technical support must be concentrated on priority theatres. This constrains the ability to sustain deterrence across several regions while reinforcing an additional theatre at short notice.

In a prolonged conflict, high sortie rates would increase wear, spare-parts demand and depot workload. Existing shortages in components, repair capacity and maintenance would reach operational units more rapidly.

Implications for NATO and Collective Defence

For NATO operators, the decisive factor is the number of F-35 aircraft actually available for air defence, ISR, targeting, suppression of enemy air defences and precision strike. The F-35 is becoming increasingly important for integrated air and missile defence, networked air operations and the integration of air, maritime and land forces.

U.S. readiness figures cannot be transferred directly to national partner fleets. Operating patterns, fleet age, maintenance structures, training cycles and national logistics differ. The structural dependency, however, is multinational.

NATO operators rely on common software baselines, common modernisation paths, shared suppliers, U.S.-centred depot structures and contractor-controlled technical data. Delays in TR-3, Block 4, spare parts, radar production or repair capacity can therefore affect several F-35 fleets simultaneously.

National air forces can influence maintenance discipline, flying-hour management and local parts prioritisation. They cannot independently accelerate software maturity, sensor production, global depot capacity or the release of technical data.

This creates an operational-readiness risk for NATO operators. At the northern and eastern flanks in particular, limited F-35 availability would constrain the ability to deploy units rapidly, sustain high sortie rates over time and offset technical losses at short notice.

The performance of the U.S.-led sustainment system is therefore becoming a factor in collective defence. National F-35 inventories strengthen deterrence only to the extent that the common supply, depot, software and maintenance architecture can convert them into available operational units.

Assessment

For U.S. Indo-Pacific Command and NATO eastern-flank planning, F-35 inventory figures must therefore be adjusted for availability: in a simultaneous multi-theatre conflict or an Article 5 scenario, the number of fully mission-capable F-35 aircraft available at short notice may remain substantially below nominal fleet strength until spare-parts supply, depot output, technical-data access and software maturity are aligned at scale.

Glossary

Mission Capable Rate
Percentage of time an aircraft can fly and perform at least one assigned task.

Full Mission Capable Rate
Percentage of time an aircraft can perform all assigned tasks without a limiting deficiency.

Technology Refresh 3
Hardware and software baseline intended to provide additional processing capacity for future F-35 capabilities.

Block 4
Modernisation pathway integrating additional sensors, weapons, mission functions, electronic-warfare capabilities, and power and cooling improvements.

AN/APG-85
New F-35 fire-control radar intended for later production lots.

Global Support Solution Reset
Joint Program Office sustainment programme intended to improve spare-parts supply, repair capacity and readiness.

Joint Program Office
U.S.-led multinational organisation responsible for F-35 programme management, acquisition and sustainment.

References

U.S. Government Accountability Office
F-35 Sustainment: Actions Needed to Ensure Updated Strategy Improves Persistent Readiness Challenges. GAO-26-108113, June 2026.
www.gao.gov/products/gao-26-108113

U.S. Government Accountability Office
F-35 Joint Strike Fighter: Actions Needed to Address Late Deliveries and Improve Future Development. GAO-25-107632, September 2025.
www.gao.gov/products/gao-25-107632

U.S. Government Accountability Office
F-35 Aircraft: DOD and the Military Services Need to Reassess the Future Sustainment Strategy. GAO-23-105341, September 2023.
www.gao.gov/products/gao-23-105341

Air & Space Forces Magazine
Marines Have 6 F-35s Without Radars; USAF Will Get Some Too, 25 June 2026.
www.airandspaceforces.com/marines-air-force-radar-less-f-35-deliveries/