The Lockheed Martin F-35 Lightning II is an American family of single-seat, single-engine, supersonic stealth strike fighters. A multirole combat aircraft designed for air superiority and strike missions, it also has electronic warfare and intelligence, surveillance, and reconnaissance capabilities. Lockheed Martin is the prime contractor, with partners Northrop Grumman and BAE Systems. The aircraft has three main variants: the conventional takeoff and landing F-35A, the short take-off and vertical-landing F-35B, and the catapult-assisted take-off but arrested recovery F-35C. With 883 aircraft in service as of 2025, it is the world's fourth-most-numerous military aircraft, and most-numerous stealth aircraft. The aircraft descends from the Lockheed Martin X-35, which in 2001 beat the Boeing X-32 to win the Joint Strike Fighter program, to replace the F-16 Fighting Falcon, F/A-18 Hornet, the McDonnell Douglas AV-8B Harrier II, and others. Development was primarily funded by the United States, with additional funding from select NATO members and Australia; Turkey was removed from the program in 2019. As of April 2026, the US operates all three main variants; both F-35As and F-35Bs are operated by Italy and Japan; F-35As are operated by Australia, Belgium, Denmark, Netherlands, Norway, Poland, and South Korea; and F-35Bs are operated by the United Kingdom. Israel operates its own F-35I variant. Six further NATO members, as well as Switzerland and Singapore, have also placed orders, and other countries are considering purchases. The program has drawn criticism for its unprecedented size, complexity, ballooning costs, and delayed deliveries, partially caused by low rate initial production during its development. As of 2024, the program is expected to cost US$2 trillion through 2088, about half of which is due to inflation. The unit flyaway costs of the 296 aircraft in lots 18-19, for which deliveries start in 2026, are $92M for the F-35A, $121.4M for the F-35B, and $110.8M for the F-35C (2026 dollars). Flyaway costs include all the basic marginal costs to produce one aircraft, including the government-furnished jet engines and radars. The F135 engine contributes $20.4 million to this flyaway cost as of 2025. The F-35 first flew in 2006; its variants entered US service in 2015 (Marine Corps F-35B), 2016 (Air Force F-35A), and 2019 (Navy F-35C). The F-35 first saw combat in the 2018 Israeli strikes in Syria, the F-35B in 2018 by US strikes in Afghanistan, and the F-35C in 2024 in US strikes in Yemen. F-35s have since been used in combat by the US in Iraq, Iran (2025 and 2026), and Venezuela; by Israel in Gaza, Iraq, Iran (2025 and 2026), Lebanon, and Yemen; and by the UK in Iraq and Syria; F-35As can deliver two US B61 nuclear bombs, including those deployed in the Netherlands and the United Kingdom. Belgium, Germany, Italy, and the UK plan to buy nuclear-capable F-35As. The US plans to buy 2,456 F-35s through 2044, which will represent the bulk of its crewed fixed-wing tactical aviation for several decades; the aircraft is to be a cornerstone of NATO and US-allied air power and operate until 2088.
Development
=== Program origins === The F-35 was the product of the Joint Strike Fighter (JSF) program, which was the merger of various combat aircraft programs from the 1980s and 1990s. One progenitor program was the Defense Advanced Research Projects Agency (DARPA) Advanced Short Take-Off/Vertical Landing (ASTOVL), which ran from 1983 to 1994; ASTOVL aimed to develop a Harrier jump jet replacement for the US Marine Corps (USMC) and the UK Royal Navy. Under one of ASTOVL's classified programs, the Supersonic STOVL Fighter (SSF), Lockheed's Skunk Works conducted research for a stealthy supersonic STOVL fighter intended for both US Air Force (USAF) and USMC; among key STOVL technologies explored was the shaft-driven lift fan (SDLF) system. Lockheed's concept was a single-engine canard delta aircraft weighing about 24,000 lb (11,000 kg) empty. ASTOVL was rechristened as the Common Affordable Lightweight Fighter (CALF) in 1993 and involved Lockheed, McDonnell Douglas, and Boeing. The end of the Cold War and the collapse of the Soviet Union in 1991 caused considerable reductions in Department of Defense (DoD) spending and subsequent restructuring. In 1993, the Joint Advanced Strike Technology (JAST) program emerged following the cancellation of the USAF's Multi-Role Fighter (MRF) and US Navy's (USN) Advanced Attack/Fighter (A/F-X) programs. MRF, a program for a relatively affordable F-16 Fighting Falcon replacement, was scaled back and delayed due to post–Cold War defense posture easing F-16 fleet usage and thus extending its service life as well as increasing budget pressure from the Lockheed Martin F-22 Advanced Tactical Fighter (ATF) program. The A/F-X, initially known as the Advanced-Attack (A-X), began in 1991 as the USN's follow-on to the Advanced Tactical Aircraft (ATA) program for a Grumman A-6 Intruder replacement; the ATA's resulting McDonnell Douglas A-12 Avenger II had been canceled due to technical problems and cost overruns in 1991. In the same year, the termination of the Naval Advanced Tactical Fighter (NATF), a naval development of USAF's ATF program to replace the Grumman F-14 Tomcat, resulted in additional fighter capability being added to A-X, which was then renamed A/F-X. Amid increased budget pressure, the DoD's Bottom-Up Review (BUR) in September 1993 announced MRF's and A/F-X's cancellations, with applicable experience brought to the emerging JAST program. JAST was not meant to develop a new aircraft, but rather to develop requirements, mature technologies, and demonstrate concepts for advanced strike warfare. As JAST progressed, the need for concept demonstrator aircraft by 1996 emerged, which would coincide with the full-scale flight demonstrator phase of ASTOVL/CALF. Because the ASTOVL/CALF concept appeared to align with the JAST charter, the two programs were eventually merged in 1994 under the JAST name, with the program now serving the USAF, USMC, and USN. JAST was subsequently renamed to Joint Strike Fighter (JSF) in 1995, with STOVL submissions by McDonnell Douglas, Northrop Grumman, Lockheed Martin, and Boeing. The JSF was expected to eventually replace large numbers of multi-role and strike fighters in the inventories of the US and its allies, including the Harrier, F-16, F/A-18, Fairchild A-10 Thunderbolt II, and Lockheed F-117 Nighthawk. International participation is a key aspect of the JSF program, starting with United Kingdom participation in the ASTOVL program. Many international partners requiring modernization of their air forces were interested in the JSF. The United Kingdom joined JAST/JSF as a founding member in 1995 and thus became the only Tier 1 partner of the JSF program; Italy, the Netherlands, Denmark, Norway, Canada, Australia, and Turkey joined the program during the Concept Demonstration Phase (CDP), with Italy and the Netherlands being Tier 2 partners and the rest Tier 3. Consequently, the aircraft was developed in cooperation with international partners and available for export.
JSF competition
Boeing and Lockheed Martin were selected in early 1997 for CDP, with their concept demonstrator aircraft designated X-32 and X-35, respectively; the McDonnell Douglas team was eliminated, and Northrop Grumman and British Aerospace joined the Lockheed Martin team. Each firm would produce two prototype air vehicles to demonstrate conventional takeoff and landing (CTOL), carrier takeoff and landing (CV), and STOVL. Lockheed Martin's design would make use of the work on the SDLF system conducted under the ASTOVL/CALF program. The key aspect of the X-35 that enabled STOVL operation, the SDLF system consists of the lift fan in the forward center fuselage that could be activated by engaging a clutch that connects the driveshaft to the turbines and thus augmenting the thrust from the engine's swivel nozzle. Research from prior aircraft incorporating similar systems, such as the Convair Model 200, Rockwell XFV-12, and Yakovlev Yak-141, was also taken into consideration. By contrast, Boeing's X-32 employed a direct lift system that the augmented turbofan would be reconfigured to when engaging in STOVL operation.
Lockheed Martin's commonality strategy was to replace the STOVL variant's SDLF with a fuel tank and the aft swivel nozzle with a two-dimensional thrust vectoring nozzle for the CTOL variant. STOVL operation is made possible through a patented shaft-driven LiftFan propulsion system. This would enable an identical aerodynamic configuration for the STOVL and CTOL variants, while the CV variant would have an enlarged wing to reduce landing speed for carrier recovery. Due to aerodynamic characteristics and carrier recovery requirements from the JAST merger, the design configuration settled on a conventional tail compared to the canard delta design from the ASTOVL/CALF; notably, the conventional tail configuration offers much lower risk for carrier recovery compared to the ASTOVL/CALF canard configuration, which was designed without carrier compatibility in mind. This enabled greater commonality between all three variants, as the commonality goal was important at this design stage. Lockheed Martin's prototypes would consist of the X-35A for demonstrating CTOL before converting it to the X-35B for STOVL demonstration and the larger-winged X-35C for CV compatibility demonstration. The X-35A first flew on 24 October 2000 and conducted flight tests for subsonic and supersonic flying qualities, handling, range, and maneuver performance. After 28 flights, the aircraft was then converted into the X-35B for STOVL testing, with key changes including the addition of the SDLF, the three-bearing swivel module (3BSM), and roll-control ducts. The X-35B would successfully demonstrate the SDLF system by performing stable hover, vertical landing, and short takeoff in less than 500 ft (150 m). The X-35C first flew on 16 December 2000 and conducted field landing carrier practice tests. On 26 October 2001, Lockheed Martin was declared the winner and was awarded the System Development and Demonstration (SDD) contract; Pratt & Whitney was separately awarded a development contract for the F135 engine for the JSF. The F-35 designation, which was out of sequence with standard DoD numbering, was allegedly determined on the spot by program manager Major General Mike Hough; this came as a surprise even to Lockheed Martin, which had expected the F-24 designation for the JSF.
Design and production
As the JSF program moved into the System Development and Demonstration phase, the X-35 demonstrator design was modified to create the F-35 combat aircraft. The forward fuselage was lengthened by 5 inches (13 cm) to make room for mission avionics, while the horizontal stabilizers were moved 2 inches (5.1 cm) aft to retain balance and control. The diverterless supersonic inlet changed from a four-sided to a three-sided cowl shape and was moved 30 inches (76 cm) aft. The fuselage section was fuller, the top surface raised by 1 inch (2.5 cm) along the centerline and the lower surface bulged to accommodate weapons bays. Following the designation of the X-35 prototypes, the three variants were designated F-35A (CTOL), F-35B (STOVL), and F-35C (CV), all with a design service life of 8,000 hours. Prime contractor Lockheed Martin performs overall systems integration and final assembly and checkout (FACO) at Air Force Plant 4 in Fort Worth, Texas, while Northrop Grumman and BAE Systems supply components for mission systems and airframe. Adding the systems of a fighter aircraft added weight. The F-35B gained the most, largely due to a 2003 decision to enlarge the weapons bays for commonality between variants; the total weight growth was reportedly up to 2,200 pounds (1,000 kg), over 8%, causing all STOVL key performance parameter (KPP) thresholds to be missed. In December 2003, the STOVL Weight Attack Team (SWAT) was formed to reduce the weight increase; changes included thinned airframe members, smaller weapons bays and vertical stabilizers, less thrust fed to the roll-post outlets, and redesigning the wing-mate joint, electrical elements, and the airframe immediately aft of the cockpit. The inlet was also revised to accommodate more powerful, greater mass flow engines. Many changes from the SWAT effort were applied to all three variants for commonality. By September 2004, these efforts had reduced the F-35B's weight by over 3,000 pounds (1,400 kg), while the F-35A and F-35C were reduced in weight by 2,400 pounds (1,100 kg) and 1,900 pounds (860 kg), respectively. The weight reduction work cost $6.2 billion and caused an 18-month delay.
The first F-35A, designated AA-1, was rolled out at Fort Worth on 19 February 2006 and first flew on 15 December 2006 with chief test pilot Jon S. Beesley at the controls. In 2006, the F-35 was given the name "Lightning II" after the Lockheed P-38 Lightning of World War II. Some USAF pilots have nicknamed the aircraft "Panther" instead, and other nicknames include "Fat Amy" and "Battle Penguin". The aircraft's software was developed as six releases, or Blocks, for SDD. The first two Blocks, 1A and 1B, readied the F-35 for initial pilot training and multi-level security. Block 2A improved the training capabilities, while 2B was the first combat-ready release planned for the USMC's Initial Operating Capability (IOC). Block 3i retains the capabilities of 2B while having new Technology Refresh 2 (TR-2) hardware and was planned for the USAF's IOC. The final release for SDD, Block 3F, would have full flight envelope and all baseline combat capabilities. Alongside software releases, each block also incorporates avionics hardware updates and air vehicle improvements from flight and structural testing. In what is known as "concurrency", some low rate initial production (LRIP) aircraft lots would be delivered in early Block configurations and eventually upgraded to Block 3F once development is complete. After 17,000 flight test hours, the final flight for the SDD phase was completed in April 2018. Like the F-22, the F-35 has been targeted by cyberattacks and technology theft efforts, as well as potential vulnerabilities in the integrity of the supply chain.
Testing found several major problems: early F-35B airframes were vulnerable to premature cracking, the F-35C arrestor hook design was unreliable, fuel tanks were too vulnerable to lightning strikes, the helmet display had problems, and more. Software was repeatedly delayed due to its unprecedented scope and complexity. In 2009, the DoD Joint Estimate Team (JET) estimated that the program was 30 months behind the public schedule. In 2011, the program was "re-baselined"; that is, its cost and schedule goals were changed, pushing the IOC from the planned 2010 to July 2015. The decision to simultaneously test, fix defects, and begin production was criticized as inefficient; in 2014, Under Secretary of Defense for Acquisition Frank Kendall called it "acquisition malpractice". The three variants shared just 25% of their parts, far below the anticipated commonality of 70%. The program received considerable criticism for cost overruns and for the total projected lifetime cost, as well as quality management shortcomings by contractors. As of August 2023, the program was 80% over budget and 10 years late. The JSF program was expected to cost about $200 billion for acquisition in base-year 2002 dollars when SDD was awarded in 2001. As early as 2005, the Government Accountability Office (GAO) had identified major program risks in cost and schedule. The costly delays strained the relationship between the Pentagon and contractors. By 2017, delays and cost overruns had pushed the F-35 program's expected acquisition costs to $406.5 billion, with total lifetime cost through 2070 to $1.5 trillion in then-year dollars, which also includes operations and maintenance. By 2024, the lifetime was extended to 2088, and the total lifetime cost was estimated at $2.1 trillion, about half of which was due to inflation. The F-35A's unit cost (not including engine) for LRIP Lot 13 was $79.2 million in base-year 2012 dollars. Delays in development and operational test and evaluation, including integration into the Joint Simulation Environment, pushed the full-rate production decision from the end of 2019 to March 2024, although actual production rate had already approached the full rate by 2020; the combined full rate at the Fort Worth, Italy, and Japan FACO plants is 156 aircraft annually.
Upgrades and further development
The F-35 is expected to be continually upgraded over its lifetime. The first combat-capable Block 2B configuration, which had basic air-to-air and strike capabilities, was declared ready by the USMC in July 2015. The Block 3F configuration began operational test and evaluation (OT&E) in December 2018, and its completion in late 2023 concluded SDD in March 2024. The F-35 program is also conducting sustainment and upgrade development, with early aircraft from LRIP lot 2 onwards gradually upgraded to the baseline Block 3F standard by 2021. With Block 3F as the final build for SDD, the first major upgrade program is Block 4, which began development in 2019 and was initially captured under the Continuous Capability Development and Delivery (C2D2) program. Block 4 is expected to enter service in incremental steps from the late 2020s to early 2030s and integrates additional weapons, including those unique to international customers, improved sensor capabilities including the new AN/APG-85 AESA radar and additional ESM bandwidth, and adds Remotely Operated Video Enhanced Receiver (ROVER) support. C2D2 also places greater emphasis on agile software development to enable quicker releases. The key enabler of Block 4 is Technology Refresh 3 (TR-3) avionics hardware, which consists of new display, core processor, and memory modules to support increased processing requirements, as well as an engine upgrade that increases the amount of cooling available to support the additional mission systems. The engine upgrade effort explored both improvements to the F135 as well as significantly more power and efficient adaptive cycle engines. In 2018, General Electric and Pratt & Whitney were awarded contracts to develop adaptive cycle engines for potential application in the F-35, and in 2022, the F-35 Adaptive Engine Replacement program was launched to integrate them. However, in 2023 the USAF chose an improved F135 under the Engine Core Upgrade (ECU) program over an adaptive cycle engine due to cost as well as concerns over risk of integrating the new engine, initially designed for the F-35A, on the B and C. Difficulties with the new TR-3 hardware, including regression testing, have caused delays to Block 4 as well as a halt in aircraft deliveries from July 2023 to July 2024. In 2023, the GAO raised concerns in two reports that the estimated cost of the Block 4 upgrade has increased from $10.6 billion to $16.5 billion and completion of the upgrade is delayed from 2026 to 2029 at the earliest. In September 2025, it was announced that the Block 4 upgrade would be truncated and delayed due to technological uncertainties and engine upgrade delays, among other reasons. Critical changes that do not require an upgraded engine will remain in Block 4 and be ready by 2031 at the earliest. Upgrades that were originally planned for Block 4, but require the upgraded engine, or lack technological maturity, will be deferred to currently undefined efforts expected in the mid-2030s. Block 4 was originally intended to be completed in 2026. Defense contractors have offered upgrades to the F-35 outside of official program contracts. In 2013, Northrop Grumman disclosed its development of a directional infrared countermeasures suite, named Threat Nullification Defensive Resource (ThNDR). The countermeasure system would share the same space as the Distributed Aperture System (DAS) sensors and act as a laser missile jammer to protect against infrared-homing missiles. The F-35 is consistently one of the most expensive weapons systems in the US military budget. It was the second-most expensive system funded in the 2025 budget, at $13.3 billion, behind the Virginia-class submarine at $13.9 billion. It was also the most expensive system in the 2026 budget request, at $13.1 billion. Israel operates a unique subvariant of the F-35A, designated the F-35I, that is designed to better interface with and incorporate Israeli equipment and weapons. The Israeli Air Force also has their own F-35I test aircraft that provides more access to the core avionics to include their own equipment. In June 2026, the US GAO released the report "F-35 Sustainment: Actions Needed to Ensure Updated Strategy Improves Persistent Readiness Challenges". The report found that F-35 fleet readiness had continued to decline despite years of investment. Fleetwide Full Mission Capable rates fell from 38 percent in fiscal year 2021 to approximately 25 percent in fiscal year 2025, while Mission Capable rates declined from 67 percent to 44 percent over the same period. The GAO identified spare parts shortages, insufficient maintenance and depot capacity, engine sustainment issues, and supply chain problems as the main contributing factors. It noted that the Department of Defense launched a $13.7 billion sustainment strategy in 2025 intended to improve readiness through 2030, but warned that the plan faces significant implementation risks and its long-term effectiveness remains uncertain.
Procurement and international participation
The United States is the primary customer and financial backer, with planned procurement of 1,763 F-35As for the USAF, 353 F-35Bs and 67 F-35Cs for the USMC, and 273 F-35Cs for the USN. Additionally, the United Kingdom, Italy, the Netherlands, Turkey, Australia, Norway, Denmark and Canada have agreed to contribute US$4.375 billion towards development costs, with the United Kingdom contributing about 10% of the planned development costs as the sole Tier 1 partner. Britain supplies ejector seats, rear fuselage, active interceptor systems, targeting lasers and weapon release cables, mainly through British Aerospace, amounting to 15% of the value of the F-35, and is the largest supplier of spare parts for the jet after the US. The initial plan was that the US and eight major partner countries would acquire over 3,100 F-35s through 2035. The three tiers of international participation generally reflect financial stake in the program, the amount of technology transfer and subcontracts open for bid by national companies, and the order in which countries can obtain production aircraft. Alongside program partner countries, Israel and Singapore have joined as Security Cooperative Participants (SCP). Sales to SCP and non-partner states, including Belgium, Japan, and South Korea, are made through the Pentagon's Foreign Military Sales program. Turkey was removed from the F-35 program in July 2019 over security concerns following its purchase of a Russian S-400 surface-to-air missile system. The unit flyaway costs of the 296 aircraft in lots 18-19, for which deliveries start in 2026, are $92M for the F-35A, $121.4M for the F-35B, and $110.8M for the F-35C (2026 dollars). Flyaway costs include all the basic marginal costs to produce one aircraft, including the government-furnished jet engines and radars (Government Furnished Equipment, or GFE, is purchased directly by the government and provided to Lockheed Martin for final assembly). The cost of the F135 engine is $20.4 million for lot 18. Lockheed Martin delivered a record 191 F-35 Lightning II fighter jets in 2025, bringing the global fleet to approximately 1,300 aircraft.
Design
=== Overview === The F-35 is a family of single-engine, supersonic, stealth, multirole strike fighters. The second fifth-generation fighter to enter US service and the first operational supersonic STOVL stealth fighter, the F-35 emphasizes low observables, advanced avionics, and sensor fusion that enable a high level of situational awareness and long range lethality; the USAF considers the aircraft its primary strike fighter for conducting suppression of enemy air defense (SEAD) and air interdiction missions, owing to the advanced sensors and mission systems.
The F-35 has a wing-tail configuration with two vertical stabilizers canted for stealth. Flight control surfaces include leading-edge flaps, flaperons, rudders, and all-moving horizontal tails (stabilators); leading edge root extensions or chines also run forward to the inlets. The relatively short 35-foot wingspan of the F-35A and F-35B is set by the requirement to fit inside USN amphibious assault ship parking areas and elevators; the F-35C's larger wing is more fuel efficient. The fixed diverterless supersonic inlets (DSI) use a bumped compression surface and forward-swept cowl to shed the boundary layer of the forebody away from the inlets, which form a Y-duct for the engine. Structurally, the F-35 drew upon lessons from the F-22; composites comprise 35% of airframe weight, with the majority being bismaleimide and composite epoxy materials as well as some carbon nanotube-reinforced epoxy in later production lots. The F-35 is considerably heavier than the lightweight fighters it replaces, with the lightest variant having an empty weight of 29,300 lb (13,300 kg); much of the weight can be attributed to the internal weapons bays and the extensive avionics carried. Each F-35 contains about 50 pounds (23 kg) of samarium magnets. While lacking the kinematic performance of the larger twin-engine F-22, the F-35 is competitive with fourth-generation fighters such as the F-16 and F/A-18, especially when they carry weapons because the F-35's internal weapons bay eliminates drag from external stores. All variants have a top speed of Mach 1.6 (1,220 mph; 1,960 km/h), attainable with full internal payload. The Pratt & Whitney F135 engine gives good subsonic acceleration and energy, with supersonic dash in afterburner. The F-35, while not a "supercruising" aircraft, can fly at Mach 1.2 (913 mph; 1,470 km/h) for a dash of 150 miles (240 km) with afterburners. This ability can be useful in battlefield situations. The large stabilators, leading edge extensions and flaps, and canted rudders provide excellent high alpha (angle-of-attack) characteristics, with a trimmed alpha of 50°. Relaxed stability and triplex-redundant fly-by-wire controls provide excellent handling qualities and departure resistance. Having over double the F-16's internal fuel, the F-35 has a considerably greater combat radius, while stealth also enables a more efficient mission flight profile. The F-35A serves as a central nuclear weapons delivery vehicle for US nuclear sharing in NATO countries, with associated USAF munitions squadrons armed with B61 Mod 12 nuclear bombs. As of 2026, these F-35A missions are active in the Netherlands at Volkel Air Base, and potentially also a USAF mission in the United Kingdom at RAF Lakenheath. Belgium, Italy, and Germany, which also host US nuclear weapons, plan to replace their nuclear-capable aircraft with F-35As. As of 2023, Kleine Brogel Air Base in Belgium operates F-16s, and Ghedi Air Base in Italy and Büchel Air Base in Germany operate Panavia Tornado PA-200s, while Aviano Air Base in Italy hosts US F-16s. The UK's Royal Air Force also plans to operate its own nuclear sharing mission, procuring F-35As to be based at RAF Marham.
Sensors and avionics
The F-35's mission systems are among the most complex aspects of the aircraft. The avionics and sensor fusion are designed to improve the pilot's situational awareness and command-and-control capabilities and facilitate network-centric warfare. Key sensors include the Northrop Grumman AN/APG-81 active electronically scanned array (AESA) radar; BAE Systems AN/ASQ-239 Barracuda electronic warfare system; Northrop Grumman/Raytheon AN/AAQ-37 Electro-optical Distributed Aperture System (DAS); Lockheed Martin AN/AAQ-40 Electro-Optical Targeting System (EOTS); and Northrop Grumman AN/ASQ-242 Communications, Navigation, and Identification (CNI) suite. The F-35 was designed for its sensors to work together to provide a cohesive image of the local battlespace; for example, the APG-81 radar also acts as part of the electronic warfare system. Much of the F-35's software was developed in C and C++ programming languages, while Ada83 code from the F-22 was also used; the Block 3F software has 8.6 million lines of code. The Green Hills Software Integrity DO-178B real-time operating system (RTOS) runs on integrated core processors (ICPs); data networking includes the IEEE 1394b and Fibre Channel buses. The avionics use commercial off-the-shelf (COTS) components when practical to make upgrades cheaper and more flexible; for example, to enable fleet software upgrades for the software-defined radio (SDR) systems. The mission systems software, particularly for sensor fusion, was one of the program's most difficult parts and responsible for substantial program delays.
The APG-81 radar uses electronic scanning for rapid beam agility and incorporates passive and active air-to-air modes, strike modes, and synthetic aperture radar (SAR) capability, with multiple target track-while-scan at ranges in excess of 80 nmi (150 km). The antenna is tilted backward for stealth. Complementing the radar is the AAQ-37 DAS: six infrared sensors that can track targets and warn of approaching missiles all around the aircraft; it acts as a situational-awareness infrared search and track (SAIRST) and feeds spherical infrared and night-vision imagery to the helmet visor. The ASQ-239 Barracuda electronic warfare system has ten radio frequency antennas embedded into the edges of the wing and tail for all-aspect radar warning receiver (RWR). It also provides sensor fusion of radio frequency and infrared tracking functions, geolocation threat targeting, and multispectral image countermeasures for self-defense against missiles. The electronic warfare system can detect and jam hostile radars. The AAQ-40 EOTS is mounted behind a faceted low-observable window under the nose and performs laser targeting, forward-looking infrared (FLIR), and long-range IRST functions. The ASQ-242 CNI suite uses a half dozen physical links, including the directional Multifunction Advanced Data Link (MADL), for covert CNI functions. Information from radio frequency receivers and infrared sensors is combined to form a single tactical picture for the pilot. The all-aspect target direction and identification can be shared via MADL to other platforms without compromising low observability, while Link 16 enables communication with older systems. The F-35 was designed to accept upgrades to its processors, sensors, and software. Technology Refresh 3, which includes a new core processor and a new cockpit display, is planned for Lot 15 aircraft. Lockheed Martin has offered the Advanced EOTS for the Block 4 configuration; the improved sensor fits into the same area as the baseline EOTS with minimal changes. In June 2018, Lockheed Martin picked Raytheon for improved DAS. The USAF has studied the potential for the F-35 to orchestrate attacks by unmanned combat aerial vehicles (UCAVs) via its sensors and communications equipment. A new radar called the AN/APG-85 is planned for Block 4 F-35s. According to the JPO, the new radar will be compatible with all three major F-35 variants. However, it is unclear if older aircraft will be retrofitted with the new radar.
Stealth and signatures
Stealth is a key aspect of the F-35's design, and radar cross-section (RCS) is minimized through careful shaping of the airframe and the use of radar-absorbent materials (RAM); visible measures to reduce RCS include alignment of edges and continuous curvature of surfaces, serration of skin panels, and the masking of the engine face and turbine. Additionally, the F-35's diverterless supersonic inlet (DSI) uses a compression bump and forward-swept cowl rather than a splitter gap or bleed system to divert the boundary layer away from the inlet duct, eliminating the diverter cavity and further reducing radar signature. The RCS of the F-35 has been characterized as lower than a metal golf ball at certain frequencies and angles; in some conditions, the F-35 compares favorably to the F-22 in stealth. For maintainability, the F-35's stealth design took lessons from earlier stealth aircraft such as the F-22; the F-35's radar-absorbent fibermat skin is more durable and requires less maintenance than older topcoats. The aircraft also has reduced infrared and visual signatures, as well as strict controls of radio frequency emitters to prevent their detection. The F-35's stealth design is primarily focused on high-frequency X-band wavelengths; low-frequency radars can spot stealthy aircraft due to Rayleigh scattering, but such radars are also conspicuous, susceptible to clutter, and lack precision. To disguise its RCS, the aircraft can mount four Luneburg lens reflectors. Overseas deployments of the F-35, including in Estonia, Bulgaria, and South Korea, use these radar reflectors to prevent Russian and Chinese intelligence gathering on the true RCS signature. There were concerns that Russian involvement in the Syrian civil war allowed the country to gather true RCS data on Israeli F-35Is flying without reflectors over Lebanon, as well as US F-22s. Noise from the F-35 caused concerns in residential areas near potential bases for the aircraft, and residents near two such bases—Luke Air Force Base, Arizona, and Eglin Air Force Base (AFB), Florida—requested environmental impact studies in 2008 and 2009, respectively. Although the noise levels, in decibels, were comparable to those of prior fighters such as the F-16, the F-35's sound power is stronger—particularly at lower frequencies. Subsequent surveys and studies have indicated that the noise of the F-35 was not perceptibly different from the F-16 and F/A-18E/F, though the greater low-frequency noise was noticeable for some observers.
Cockpit
The glass cockpit was designed to give the pilot good situational awareness. The main display is a 20-by-8-inch (50 by 20 cm) panoramic touchscreen, which shows flight instruments, stores management, CNI information, and integrated caution and warnings; the pilot can customize the arrangement of the information. Below the main display is a smaller stand-by display. The cockpit has a speech-recognition system developed by Adacel. The F-35 does not have a head-up display; instead, flight and combat information is displayed on the visor of the pilot's helmet in a helmet-mounted display system (HMDS). The one-piece tinted canopy is hinged at the front and has an internal frame for structural strength. The Martin-Baker US16E ejection seat is launched by a twin-catapult system housed on side rails. There is a right-hand side stick and throttle hands-on throttle-and-stick system. For life support, an onboard oxygen-generation system (OBOGS) is fitted and powered by the Integrated Power Package (IPP), with an auxiliary oxygen bottle and backup oxygen system for emergencies.
The Vision Systems International helmet display is a key piece of the F-35's human-machine interface. Instead of the head-up display mounted atop the dashboard of earlier fighters, the HMDS puts flight and combat information on the helmet visor, allowing the pilot to see it no matter which way they are facing. Infrared and night vision imagery from the Distributed Aperture System can be displayed directly on the HMDS and enables the pilot to "see through" the aircraft. The HMDS allows an F-35 pilot to fire missiles at targets even when the nose of the aircraft is pointing elsewhere by cuing missile seekers at high angles off-boresight. Each helmet costs $400,000. The HMDS weighs more than traditional helmets, and there is concern that it can endanger lightweight pilots during ejection. Due to the HMDS's vibration, jitter, night-vision and sensor display problems during development, Lockheed Martin and Elbit issued a draft specification in 2011 for an alternative HMDS based on the AN/AVS-9 night vision goggles as backup, with BAE Systems chosen later that year. A cockpit redesign would be needed to adopt an alternative HMDS. Following progress on the baseline helmet, development on the alternative HMDS was halted in October 2013. In 2016, the Gen 3 helmet with improved night vision camera, new liquid crystal displays, automated alignment and software enhancements was introduced with LRIP lot 7.
Armament
To preserve its stealth shaping, the F-35 has two internal weapons bays, each with two weapons stations. The two outboard weapon stations each can carry ordnance up to 2,500 lb (1,100 kg), or 1,500 lb (680 kg) for the F-35B, while the two inboard stations carry air-to-air missiles. Air-to-surface weapons for the outboard station include the Joint Direct Attack Munition (JDAM), Paveway series of bombs, Joint Standoff Weapon (JSOW), and cluster munitions (Wind Corrected Munitions Dispenser). The station can also carry multiple smaller munitions, such as the GBU-39 Small Diameter Bombs (SDB), GBU-53/B StormBreaker and SPEAR 3; up to four SDBs can be carried per station for the F-35A and F-35C, and three for the F-35B. The F-35A achieved certification to carry the B61 Mod 12 nuclear bomb in October 2023. The inboard station can carry the AIM-120 AMRAAM and eventually the AIM-260 JATM. Two compartments behind the weapons bays contain flares, chaff, and towed decoys.
The aircraft can use six external weapons stations for missions that do not require stealth; a configuration dubbed "beast mode" by Lockheed Martin. The wingtip pylons each can carry an AIM-9X or AIM-132 ASRAAM and are canted outwards to reduce their radar cross-section. Additionally, each wing has a 5,000 lb (2,300 kg) inboard station and a 2,500 lb (1,100 kg) middle station, or 1,500 lb (680 kg) for F-35B. The external wing stations can carry large air-to-surface weapons that would not fit inside the weapons bays such as the AGM-158 Joint Air to Surface Standoff Missile (JASSM) or AGM-158C LRASM cruise missile. An air-to-air missile load of eight AIM-120s and two AIM-9s is possible using internal and external weapons stations; a configuration of six 2,000 lb (910 kg) bombs, two AIM-120s and two AIM-9s can also be arranged. The F-35 is armed with a 25 mm GAU-22/A rotary cannon, a lighter four-barrel variant of the GAU-12/U Equalizer. On the F-35A, this is mounted internally near the left wing root with 182 rounds carried; the gun is more effective against ground targets than the 20 mm gun carried by other USAF fighters. In 2020, a USAF report noted "unacceptable" accuracy problems with the GAU-22/A on the F-35A. These were due to "misalignments" in the gun's mount, which was also susceptible to cracking. These problems were resolved by 2024. The F-35B and F-35C have no internal gun and instead can use a Terma A/S multi-mission pod (MMP) carrying the GAU-22/A and 220 rounds; the pod is mounted on the centerline of the aircraft and shaped to reduce its radar cross-section. In lieu of the gun, the pod can also be used for different equipment and purposes, such as electronic warfare, aerial reconnaissance, or rear-facing tactical radar. The pod was not susceptible to the accuracy issues that once plagued the gun on the F-35A variant, though it was apparently not problem-free. Lockheed Martin is developing a weapon rack called Sidekick that would enable the internal outboard station to carry two AIM-120s, thus increasing the internal air-to-air payload to six missiles, currently offered for Block 4. Block 4 will also have a rearranged hydraulic line and bracket to allow the F-35B to carry four SDBs per internal outboard station; integration of the MBDA Meteor is also planned. The USAF and USN are planning to integrate the AGM-88G AARGM-ER internally in the F-35A and F-35C. Norway and Australia are funding an adaptation of the Naval Strike Missile (NSM) for the F-35; designated Joint Strike Missile (JSM), two missiles can be carried internally with an additional four externally. Both hypersonic missiles and directed-energy weapons such as solid-state lasers are currently being considered as future upgrades; in 2024, Lockheed Martin disclosed its proposed Mako hypersonic missile, which can be carried internally in the F-35A and C and externally on the B. Additionally, Lockheed Martin is studying integrating a fiber laser that uses spectral beam combining multiple individual laser modules into a single high-power beam, which can be scaled to various levels.
The USAF plans for the F-35A to take up the close air support (CAS) mission in contested environments; amid criticism that it is not as well suited as a dedicated attack platform, USAF chief of staff Mark Welsh placed a focus on weapons for CAS sorties, including guided rockets, fragmentation rockets that shatter into individual projectiles before impact, and more compact ammunition for higher capacity gun pods. Fragmentary rocket warheads create greater effects than cannon shells as each rocket creates a "thousand-round burst", delivering more projectiles than a strafing run. As of 2022, the most common armaments across air forces are the AIM-120 AMRAAM, used by all F-35 operators except the Czech Republic and Finland, and the GBU-31 family of 2,000-pound JDAM bombs, used by all operators except the Czech Republic and the United Kingdom.
=== Engine === The aircraft is powered by a single Pratt & Whitney F135 low-bypass augmented turbofan with a rated thrust of 28,000 lbf (125 kN) at military power and 43,000 lbf (191 kN) with afterburner. Derived from the Pratt & Whitney F119 used by the F-22, the F135 has a larger fan and higher bypass ratio to increase subsonic thrust and fuel efficiency, and unlike the F119, is not optimized for supercruise. The engine contributes to the F-35's stealth by having a low-observable augmenter, or afterburner, that incorporates fuel injectors into thick curved vanes; these vanes are covered by ceramic radar-absorbent materials and mask the turbine. The stealthy augmenter had problems with pressure pulsations, or "screech", at low altitude and high speed early in its development. The low-observable axisymmetric nozzle consists of 15 partially overlapping flaps that create a sawtooth pattern at the trailing edge, which reduces radar signature and creates shed vortices that reduce the infrared signature of the exhaust plume. The engine's large size forced the Navy to change its underway replenishment system to bring new engines aboard at sea. The F-35's Integrated Power Package (IPP) performs power and thermal management and integrates environmental control, auxiliary power unit, engine starting, and other functions into a single system.
The F135-PW-600 variant for the F-35B incorporates the Shaft-Driven Lift Fan (SDLF) to allow STOVL operations. Designed by Lockheed Martin and developed by Rolls-Royce, the SDLF, also known as the Rolls-Royce LiftSystem, consists of the lift fan, drive shaft, two roll posts, and a "three-bearing swivel module" (3BSM). The nozzle features three bearings resembling a short cylinder with nonparallel bases. As the toothed edges are rotated by motors, the nozzle swivels from being linear with the engine to being perpendicular. The thrust vectoring 3BSM nozzle allows the main engine exhaust to be deflected downward at the tail of the aircraft and is moved by a "fueldraulic" actuator that uses pressurized fuel as the working fluid. Unlike the Harrier's Pegasus engine that entirely uses direct engine thrust for lift, the F-35B's system augments the swivel nozzle's thrust with the lift fan; the fan is powered by the low-pressure turbine through a drive shaft when engaged with a clutch and placed near the front of the aircraft to provide a torque countering that of the 3BSM nozzle. Roll control during slow flight is achieved by diverting unheated engine bypass air through wing-mounted thrust nozzles called roll posts. An alternative engine, the General Electric/Allison/Rolls-Royce F136, was being developed in the 1990s and 2000s; originally, F-35 engines from Lot 6 onward were competitively tendered. Using technology from the General Electric YF120, the F136 was claimed to have a greater temperature margin than the F135 due to the higher mass flow design making full use of the inlet. The F136 was canceled in December 2011 due to lack of funding. The F-35 is expected to receive propulsion upgrades over its lifecycle to adapt to emerging threats and enable additional capabilities. In 2016, the Adaptive Engine Transition Program (AETP) was launched to develop and test adaptive cycle engines, with one major potential application being the re-engining of the F-35; in 2018, both GE and P&W were awarded contracts to develop 45,000 lbf (200 kN) thrust class demonstrators, with the designations XA100 and XA101 respectively. In addition to potential re-engining, P&W is also developing improvements to the baseline F135; the Engine Core Upgrade (ECU) is an update to the power module, originally called Growth Option 1.0 and then Engine Enhancement Package, that improves engine thrust and fuel burn by 5% and bleed air cooling capacity by 50% to support Block 4. The F135 ECU was selected over AETP engines in 2023 to provide additional power and cooling for the F-35. Although GE had expected that the more revolutionary XA100 could enter service with the F-35A and C by 2027 and could be adapted for the F-35B, the increased cost and risk caused the USAF to choose the F135 ECU instead.
=== Maintenance and logistics === The F-35 is designed to require less maintenance than earlier stealth aircraft. Some 95% of all field-replaceable parts are "one deep"—that is, nothing else needs to be removed to reach the desired part; for instance, the ejection seat can be replaced without removing the canopy. The F-35 has a fibermat radar-absorbent material (RAM) baked into the skin, which is more durable, easier to work with, and faster to cure than older RAM coatings; similar coatings are being considered for application on older stealth aircraft such as the F-22. Skin corrosion on the F-22 led to the F-35 using a less galvanic corrosion-inducing skin gap filler, fewer gaps in the airframe skin needing filler, and better drainage. The flight control system uses electro-hydrostatic actuators rather than traditional hydraulic systems; these controls can be powered by lithium-ion batteries in an emergency. Commonality between variants led to the USMC's first aircraft maintenance Field Training Detachment, which applied USAF lessons to their F-35 operations. The F-35 was initially supported by a computerized maintenance management system named Autonomic Logistics Information System (ALIS). In concept, any F-35 can be serviced at any maintenance facility and all parts can be globally tracked and shared as needed. In September 2026, a shipment of F-35 components sent from Australia to the United States for repair was diverted to Hong Kong, prompting investigations by U.S. and Australian authorities amid concerns that the components could potentially expose sensitive F-35 technology. The Pentagon's F-35 Joint Program Office said it was working with U.S. authorities and industry partners to retrieve the components and investigate the incident. Australia said it was assisting the investigation, while its defence minister said the missing components were not believed to be sensitive. Due to numerous problems, such as unreliable diagnoses, excessive connectivity requirements, and security vulnerabilities, ALIS is being replaced by the cloud-based Operational Data Integrated Network (ODIN). From September 2020, ODIN base kits (OBKs) were running ALIS software, as well as ODIN software, first at Marine Corps Air Station (MCAS) Yuma, Arizona, then at Naval Air Station Lemoore, California, in support of Strike Fighter Squadron (VFA) 125 on 16 July 2021, and then Nellis Air Force Base, Nevada, in support of the 422nd Test and Evaluation Squadron (TES) on 6 August 2021. In 2022, over a dozen more OBK sites will replace the ALIS's Standard Operating Unit unclassified (SOU-U) servers. OBK performance is double that of ALIS.
Operational history
=== Testing === The first F-35A, AA-1, conducted its engine run in September 2006 and first flew on 15 December 2006. Unlike subsequent aircraft, AA-1 did not have the weight optimization from SWAT, so it mainly tested subsystems common to subsequent aircraft, such as the propulsion, electrical system, and cockpit displays. This aircraft was retired from flight testing in December 2009 and was used for live-fire testing at NAS China Lake.
The first F-35B, BF-1, first flew on 11 June 2008, first hovered on 17 March 2010, and first landed vertically the next day. The first weight-optimized F-35A, AF-1, flew on 14 November 2009, and the first such F-35C, CF-1, on 6 June 2010. The F-35 Integrated Test Force (ITF) consisted of 18 aircraft at Edwards Air Force Base and Naval Air Station Patuxent River. At Edwards, five F-35As, three F-35Bs, and one F-35 performed flight sciences testing such as F-35A envelope expansion, flight loads, stores separation, as well as mission systems testing. At Patuxent River, five F-35Bs and four F-35Cs handled their variants' envelope expansion and STOVL and CV suitability testing. Additional carrier suitability testing was conducted at Naval Air Warfare Center Aircraft Division at Lakehurst, New Jersey. Two non-flying aircraft of each variant were used to test static loads and fatigue. The Lockheed Martin CATBird, a modified Boeing 737-300 with a duplication of the cockpit, has been used to test avionics and mission systems. Field testing of the F-35's sensors was conducted during Exercise Northern Edge 2009 and 2011, serving as risk-reduction steps. Flight tests revealed deficiencies that caused delays, costly redesigns, and several fleet-wide groundings. In 2011, the F-35C failed to catch the arresting wire in all eight landing tests; a redesigned tail hook was delivered two years later. By June 2009, many of the initial flight test targets had been accomplished, but the program was behind schedule. Software and mission systems were among the biggest sources of delays for the program, with sensor fusion proving especially challenging. In fatigue testing, the F-35B suffered several premature cracks, requiring a redesign of the structure. A third non-flying F-35B was planned to test the redesigned structure. Prolonged afterburner use was found to damage the horizontal tails of the F-35B and C. Early flight control laws had problems with "wing drop" and also made the airplane sluggish, with high angles-of-attack tests in 2015 against an F-16 showing a lack of energy.
At-sea testing of the F-35B was first conducted aboard USS Wasp. In October 2011, two F-35Bs conducted three weeks of initial sea trials, called Development Test I. The second F-35B sea trials, Development Test II, began in August 2013; two aircraft completed 19 nighttime vertical landings using DAS imagery. The first operational testing involving six F-35Bs was done on the Wasp in May 2015. The final Development Test III on USS America, with operations in high sea states, was completed in late 2016. A Royal Navy F-35 conducted the first "rolling" landing on board HMS Queen Elizabeth in October 2018.
After the redesigned tail hook arrived, the F-35C's carrier-based Development Test I began in November 2014 aboard USS Nimitz; it focused on basic day carrier operations and establishing launch and recovery handling procedures. Development Test II, which focused on night operations, weapons loading, and full power launches, took place in October 2015. The final Development Test III was completed in August 2016, and included tests of asymmetric loads and certifying systems for landing qualifications and interoperability. Operational test of the F-35C was conducted in 2018, and the first operational squadron achieved safe-for-flight milestone that December, paving the way for its introduction in 2019. The F-35's reliability and availability have fallen short of requirements, especially in the early years of testing. The ALIS maintenance and logistics system was plagued by excessive connectivity requirements and faulty diagnoses. In late 2017, the GAO reported the time needed to repair an F-35 part averaged 172 days, which was "twice the program's objective", and that shortage of spare parts was degrading readiness. In 2019, while individual F-35 units have achieved mission-capable rates of over the target of 80% for short periods during deployed operations, fleet-wide rates remained below target. The fleet availability goal of 65% was also not met, although the trend shows improvement. Internal gun accuracy of the F-35A was unacceptable until misalignment issues were addressed by 2024. As of 2020, the number of the program's most serious issues has been decreased by half. Operational test and evaluation (OT&E) with Block 3F, the final configuration for SDD, began in December 2018, but its completion was delayed particularly by technical problems in integration with the DOD's Joint Simulation Environment (JSE); the F-35 finally completed all JSE trials in September 2023.
United States
Training
The F-35A and F-35B were cleared for basic flight training in early 2012, despite concerns that the system's immaturity could reduce safety and performance. During the Low Rate Initial Production (LRIP) phase, the three US military services jointly developed tactics and procedures using flight simulators, testing effectiveness, discovering problems, and refining design. On 10 September 2012, the USAF began an operational utility evaluation (OUE) of the F-35A, including logistical support, maintenance, personnel training, and pilot execution.
