Lockheed Martin F-22 Raptor

The Lockheed Martin F-22 Raptor is an American single-seat, twin-engine, supersonic all-weather stealth fighter aircraft developed for the United States Air Force (USAF). As a product of the USAF's Advanced Tactical Fighter (ATF) program the aircraft was designed as an air superiority fighter, but also incorporates ground attack, electronic warfare, and signals intelligence capabilities. The prime contractor, Lockheed Martin, built most of the F-22's airframe and weapons systems and conducted final assembly, while Boeing provided the wings, aft fuselage, avionics integration, and training systems.

The aircraft first flew in 1997 and was variously designated F-22 and F/A-22 before it formally entered service in December 2005 as the F-22A. Although the USAF had originally planned to buy a total of 750 ATFs, the program was cut to 187 production aircraft in 2009 due to high costs, a lack of air-to-air missions at the time of production, and the development of the more affordable and versatile F-35. The last F-22 was delivered in 2012.

While it had a protracted development and initial operational difficulties, the F-22 has become a critical component of the USAF's tactical airpower. The fighter's combination of stealth, aerodynamic performance, and mission systems enabled a leap in air combat capabilities and set the benchmark for its generation.

## Development

### Origins

In 1981, the U.S. Air Force identified a requirement for an Advanced Tactical Fighter (ATF) to replace the F-15 Eagle and F-16 Fighting Falcon. Code-named "Senior Sky", this air-superiority fighter program was influenced by intelligence reports of emerging worldwide threats emanating from the Soviet Union, including new developments in Soviet air defense systems, the introduction of the Beriev A-50 "Mainstay" airborne early warning and control (AEW&C) aircraft, and the proliferation of the Sukhoi Su-27 "Flanker"- and Mikoyan MiG-29 "Fulcrum"-class of fighter aircraft. The ATF would have to perform offensive and defensive counter-air operations (OCA/DCA) in this highly contested environment; to do so, it would make an ambitious leap in performance by taking advantage of the new technologies in fighter design on the horizon, including composite materials, lightweight alloys, advanced flight control systems and avionics, more powerful propulsion systems for supersonic cruise (or supercruise) over Mach 1.5, and most importantly, stealth technology.

The USAF initiated an ATF request for information (RFI) to the aerospace industry in May 1981 as well as a subsequent concept development team (CDT) to manage concept and technology development. In 1983, the CDT became the ATF System Program Office (SPO) and managed the program at Wright-Patterson Air Force Base. Following a period of concept refinement and system requirements definition, the demonstration and validation (Dem/Val) request for proposals (RFP) was issued in September 1985, with requirements placing a strong emphasis on stealth and supercruise. The RFP would see some alterations after its first release; stealth requirements were drastically increased in December 1985, and the requirement for flying technology demonstrator prototypes was added in May 1986. Additionally, the U.S. Navy, under the Navalized Advanced Tactical Fighter (NATF) program, eventually announced that it would use an ATF derivative to replace its F-14 Tomcat. Owing to the immense investments required to develop the technology needed to achieve performance requirements, teaming between companies was encouraged. Of the seven bidding companies, Lockheed and Northrop were selected on 31 October 1986. Lockheed, through its Skunk Works division, then teamed with Boeing and General Dynamics while Northrop teamed with McDonnell Douglas, and the two contractor teams undertook a 50-month Dem/Val phase, culminating in the flight test of two technology demonstrator prototypes, the YF-22 and the YF-23, respectively. Concurrently, Pratt & Whitney and General Electric were contracted to develop the propulsion systems for the ATF engine competition.

Dem/Val was focused on system engineering, technology development plans, and risk reduction over point aircraft designs; in fact, after the down-select, the Lockheed team completely redesigned the airframe configuration in the summer of 1987 due to weight analysis during detailed design, with notable changes including the wing planform from swept trapezoidal to diamond-like delta and a reduction in forebody planform area. Contractors made extensive use of analytical and empirical methods, including computational fluid dynamics, wind-tunnel testing, and radar cross-section (RCS) calculations and pole testing; the Lockheed team would conduct nearly 18,000 hours of wind-tunnel testing for Dem/Val. Avionics development was marked by extensive testing and prototyping and supported by ground and flying laboratories. During Dem/Val, the SPO used the results of performance and cost trade studies conducted by contractor teams to adjust ATF requirements and delete ones that were significant weight and cost drivers while having marginal value. The short takeoff and landing (STOL) requirement was relaxed to delete thrust-reversers, saving substantial weight. As avionics was a major cost driver, side looking radars were deleted, and the dedicated infrared search and track (IRST) system was downgraded from multicolor to single color and then deleted as well. Space and cooling provisions were retained to allow for the later addition of these components. The ejection seat requirement was downgraded from a fresh design to the existing McDonnell Douglas ACES II. Despite efforts by the contractor teams to rein in weight, the takeoff gross weight estimate was increased from 50,000 to 60,000 lb (23,000 to 27,000 kg), resulting in engine thrust requirement increasing from 30,000 to 35,000 lbf (130 to 160 kN) class.

Each team built two prototype air vehicles for Dem/Val, one for each of the two engine options. The YF-22 had its maiden flight on 29 September 1990 and in flight tests successfully demonstrated supercruise as well as the firing of air-to-air missiles from internal weapons bays. After the Dem/Val flight test of the prototypes, on 23 April 1991, Secretary of the USAF Donald Rice announced the Lockheed team and Pratt & Whitney as the winners of the ATF and engine competitions for full-scale development. The YF-23 design was considered stealthier and faster, while the YF-22, with its thrust vectoring nozzles, was more maneuverable as well as less expensive and risky. The press also speculated that the Lockheed team's design was also more adaptable to the Navy's NATF, but by fiscal year (FY) 1992, the Navy had abandoned NATF.

### Full-scale development

As the program moved to full-scale development, or Engineering & Manufacturing Development (EMD), the production F-22 design evolved to have notable differences from the immature YF-22 demonstrator, despite having a similar configuration. The wing's leading edge sweep angle was decreased from 48° to 42°, while the vertical stabilizers were shifted rearward and decreased in area by 20%. The radome shape was changed for better radar performance and the wingtips were clipped for antennas. To improve pilot visibility and aerodynamics, the canopy was moved forward 7 inches (18 cm) and the engine inlets moved rearward 14 inches (36 cm). The shapes of the fuselage, wing, and stabilator trailing edges were refined to improve aerodynamics, strength, and stealth characteristics. The production airframe was designed with a service life of 8,000 hours. Increasing weight during EMD caused slight reductions in projected range and maneuver performance.

Aside from advances in air vehicle and propulsion technology, the F-22's avionics and software were unprecedented in terms of complexity and scale, with the fusion of multiple sensors systems and software integration of 1.7 million lines of code. To enable early looks and troubleshooting for mission software development, the software was flight-tested on a Boeing 757 modified with F-22 mission systems to serve as the Flying Test Bed avionics laboratory.

The end of the Cold War and the dissolution of the Soviet Union in 1991 reduced the Department of Defense's (DoD) urgency for new weapon systems and the following years would see successive reductions in DoD spending; this resulted in the F-22's EMD being rescheduled and lengthened multiple times. The roughly equal division of work amongst the team largely carried through from Dem/Val to EMD, although prime contractor Lockheed acquired General Dynamics' fighter portfolio at Fort Worth, Texas in 1993 and thus had the majority of the airframe manufacturing; Lockheed would merge with Martin Marietta in 1995 to form Lockheed Martin. While Lockheed primarily performed Dem/Val work at its Skunk Works sites in Burbank and Palmdale, California, it would shift its program office and EMD work from Burbank to Marietta, Georgia, where it performed final assembly; program partner Boeing provided additional airframe components as well as avionics integration and training systems in Seattle, Washington. The first F-22, an EMD aircraft with tail number 4001, was unveiled at Dobbins Air Reserve Base in Marietta on 9 April 1997 and first flew on 7 September 1997.

The numerous new technologies needed for the F-22's ambitious performance requirements resulted in substantial cost overruns and delays; issues with meeting scheduled milestones were exacerbated by post-Cold War funding cuts in the 1990s. Furthermore, many capabilities were deferred to post-service upgrades, reducing the initial cost but increasing total program cost. Following extensive tests and evaluations, EMD transitioned to full-rate production in March 2005 while Research, Development, Test, and Evaluation (RTD&E) activity continued for upgrades and modifications. In 2006, the F-22 development team won the Collier Trophy, American aviation's most prestigious award. Due to the aircraft's sophisticated capabilities, contractors have been targeted by cyberattacks and technology theft.

### Production and procurement

The USAF originally envisioned ordering 750 ATFs at a total program cost of \$44.3 billion and procurement cost of \$26.2 billion in FY 1985 dollars, with production beginning in 1994 and service entry in the late 1990s. The 1990 Major Aircraft Review led by Secretary of Defense Dick Cheney reduced this to 648 aircraft beginning in 1996 and in service in the early-to-mid 2000s. After the end of the Cold War, this was further curtailed to 442 in the 1993 Bottom-Up Review while the USAF eventually set its requirement to 381 to adequately support its Air Expeditionary Force structure with last delivery in 2013. However, funding instability had reduced the total to 339 by 1997 and production was nearly halted by Congress in 1999. Although production funds were eventually restored, the planned number continued to decline due to delays and cost overruns during EMD, slipping to 277 by 2003. In 2004, with its focus on asymmetric counterinsurgency warfare in Iraq and Afghanistan, the DoD under Secretary Donald Rumsfeld further cut the planned F-22 procurement to 183 production aircraft, despite the USAF's requirement for 381. A multi-year procurement contract was awarded in 2006 to bring the number to 183, which would be distributed to seven combat squadrons; total program cost was projected to be \$62 billion. In 2008, Congress passed a defense spending bill that raised the total orders for production aircraft to 187.

F-22 production would support over 1,000 subcontractors and suppliers from 46 states and up to 95,000 jobs, and spanned 15 years at a peak rate of roughly two airplanes per month, about half of the initially planned rate; after EMD aircraft contracts, the first production lot was awarded in September 2000. As production wound down in 2011, the total program cost was estimated to be about \$67.3 billion (about \$360 million for each production aircraft delivered), with \$32.4 billion spent on Research, Development, Test and Evaluation (RDT&E) and \$34.9 billion on procurement and military construction (MILCON) in then year dollars. The incremental cost for an additional F-22 was estimated at \$138 million in 2009.

In total, 195 F-22s were built. The first two were EMD aircraft in the Block 1.0 configuration for initial flight testing and envelope expansion, while the third was a Block 2.0 aircraft built to represent the internal structure of production airframes and enabled it to test full flight loads. Six more EMD aircraft were built in the Block 10 configuration for development and upgrade testing, with the last two considered essentially production quality jets. Production for operational squadrons consisted of 74 Block 10/20 training aircraft and 112 Block 30/35 combat aircraft for a total of 186 (or 187 when accounting for production representative test vehicles); one of the Block 30 aircraft is dedicated to flight sciences at Edwards Air Force Base, California. Block 20 aircraft from Lot 3 onward were upgraded to Block 30 standards under the Common Configuration Plan, increasing the Block 30/35 fleet to 149 aircraft while 37 remain in the Block 20 configuration.

### Ban on exports

The F-22 cannot be exported under US federal law to protect its stealth technology and classified features. Customers for U.S. fighters are acquiring earlier designs such as the F-15 Eagle and F-16 Fighting Falcon or the newer F-35 Lightning II, which contains technology from the F-22 but was designed to be cheaper, more flexible, and available for export. In September 2006, Congress upheld the ban on foreign F-22 sales. Despite the ban, the 2010 defense authorization bill included provisions requiring the DoD to report on the costs and feasibility for an F-22 export variant, and another report on the effect of F-22 export sales on the US aerospace industry.

Some Australian politicians and defense commentators proposed that Australia should attempt to purchase F-22s instead of the planned F-35s, citing the F-22's known capabilities and F-35's delays and developmental uncertainties. The Royal Australian Air Force (RAAF) soon determined that the F-22 was unable to perform the F-35's strike and close air support roles.

The Japanese government also showed interest in the F-22 for its Replacement-Fighter program. The Japan Air Self-Defense Force (JASDF) would reportedly require fewer fighters for its mission if it obtained the F-22, thus reducing engineering and staffing costs. In 2009 it was reported that acquiring the F-22 would require increases to the Japanese government's defense budget beyond the historical 1 percent of its GDP. With the end of F-22 production, Japan chose the F-35 in December 2011. Israel also expressed interest, but eventually chose the F-35 because of the F-22's price and unavailability.

### Production termination

Throughout the 2000s when the Department of Defense was primarily fighting counterinsurgency wars in Iraq and Afghanistan, the USAF's procurement goal of 381 F-22s was questioned over rising costs, initial reliability and availability problems, limited multirole versatility, and a lack of relevant adversaries for air combat missions. In 2006, Comptroller General of the United States David Walker found that "the DoD has not demonstrated the need" for more investment in the F-22, and further opposition was expressed by Bush Administration Secretary of Defense Rumsfeld and his successor Robert Gates, Deputy Secretary of Defense Gordon R. England, and Chairman of U.S. Senate Armed Services Committee (SASC) Senators John Warner and John McCain. Under Rumsfeld, procurement was severely cut to 183 aircraft. The F-22 lost influential supporters in 2008 after the forced resignations of Secretary of the Air Force Michael Wynne and the Chief of Staff of the Air Force General T. Michael Moseley. In November 2008, Gates stated that the F-22 lacked relevance in asymmetric post-Cold War conflicts, and in April 2009, under the Obama Administration, he called for production to end in FY 2011 after completing 187 F-22s.

The loss of staunch F-22 advocates in the upper DoD echelons resulted in the erosion of its political support. In July 2008, General James Cartwright, Vice Chairman of the Joint Chiefs of Staff, stated to the SASC his reasons for supporting the termination of F-22 production, including shifting resources to the multi-service F-35 and preserving the F/A-18 production line for the EA-18G Growler's electronic warfare capabilities. Although Russian and Chinese fighter developments fueled concern for the USAF, Gates dismissed this and in 2010, he set the F-22 requirement to 187 aircraft by lowering the number of major regional conflict preparations from two to one, despite an effort by Moseley's successor General Norton Schwartz to raise the number of aircraft to 243. After President Barack Obama threatened to veto further production at Gates' urging, the Senate voted in July 2009 in favor of ending production and the House agreed to abide by the 187 cap. Gates highlighted the F-35's role in the decision, and in 2011, he explained that Chinese fighter developments had been accounted for when the F-22 numbers were set, and that the U.S. would have a considerable advantage in stealth aircraft in 2025 even with F-35 delays. In December 2011, the 195th and final F-22 was completed out of 8 test and 187 production aircraft built; the jet was delivered on 2 May 2012. The curtailed procurement would force the USAF to operate the F-15C/D into the 2020s in order to retain adequate numbers of air superiority fighters.

Although production ended, F-22 tooling was retained for supporting repairs and maintenance as well as the possibility of a production restart or a Service Life Extension Program (SLEP). A RAND Corporation paper from a 2010 USAF study estimated that restarting production and building an additional 75 F-22s would cost \$17 billion, resulting in \$227 million per aircraft, \$54 million higher than the flyaway cost. At that time, Lockheed Martin stated that restarting the production line itself would cost about \$200 million. Production tooling and associated documentation were subsequently stored at the Sierra Army Depot to support the fleet life cycle while its Marietta plant space was repurposed to support the C-130J and F-35; engineering work for sustainment and upgrades continued at Fort Worth, Texas and Palmdale, California.

In April 2016, the House Armed Services Committee (HASC) Tactical Air and Land Forces Subcommittee, citing advances in air warfare systems of Russia and China, directed the USAF to conduct a cost study and assessment associated with resuming production of the F-22. On 9 June 2017, the USAF submitted their report to Congress stating they had no plans to restart the F-22 production line due to economic and logistical challenges; it estimated it would cost approximately \$50 billion to procure 194 additional F-22s at a cost of \$206–216 million per aircraft, including approximately \$9.9 billion for non-recurring start-up costs and \$40.4 billion for aircraft procurement costs with the first delivery in the mid-to-late 2020s. The long time gap since the end of production meant hiring new workers and sourcing replacement vendors, contributing to the high start-up costs and lead times. The USAF believed that the funding would be better invested in its next-generation Air Superiority 2030 effort, which evolved into the Next Generation Air Dominance.

### Continued developments and upgrades

The F-22 and its subsystems were designed to be upgraded over its life cycle in anticipation for technological advances and evolving threats. The modernization and upgrades consist of software and hardware modifications captured under numbered Increments, originally called Spirals, as well as software-only Operational Flight Program (OFP) Updates. Amid debates over the airplane's relevance in asymmetric counterinsurgency warfare, the first Increments and OFP Updates primarily focused on ground attack, or strike capabilities. Increment 2, the first upgrade program, was implemented in 2005 for Block 20 aircraft onward and enabled the employment of Joint Direct Attack Munitions (JDAM). The improved AN/APG-77(V)1 radar, which incorporates air-to-ground modes, was certified in March 2007 and fitted on airframes from Lot 5 onward. Increment 3.1 and Updates 3 and 4 for Block 30/35 aircraft improved ground-attack capabilities through synthetic aperture radar (SAR) mapping and radio emitter direction finding, electronic attack and Small Diameter Bomb (SDB) integration; testing began in 2009 and the first upgraded aircraft was delivered in 2011. To address oxygen deprivation issues, F-22s were fitted with an automatic backup oxygen system (ABOS) and modified life support system starting in 2012.

In contrast to prior upgrades, Increment 3.2 for Block 30/35 aircraft emphasized air combat capabilities and was a two-part process. 3.2A focused on electronic warfare, communications and identification, while 3.2B included geolocation improvements and full integration of the AIM-9X and AIM-120D; fleet releases began in 2013 and 2019, respectively. Concurrent with Increment 3.2, Update 5 in 2016 added Automatic Ground Collision Avoidance System (AGCAS), datalink updates, and more. Update 6, deployed in tandem with 3.2B, incorporated cryptographic and avionics stability enhancements. Following 3.2B, an open mission system (OMS) processor module and architecture were added and an agile software development process was implemented to enable faster enhancements from additional vendors. The Multifunctional Information Distribution System-Joint Tactical Radio System (MIDS-JTRS) for Tactical Mandates, including Mode 5 IFF, and Link 16 traffic was installed starting in 2021, and the airplane can also use the Battlefield Airborne Communications Node (BACN) as a two-way communication gateway.

Additional modernization and enhancements are under development, with funding currently extending to 2031. Upgrades currently being tested include new sensors and antennas as well as reliability improvements such as more durable stealth coatings; the dedicated advanced IRST, originally deleted during Dem/Val, is one of the new sensors added. Other enhancements being developed include all-aspect IRST functionality for the Missile Launch Detector (MLD), manned-unmanned teaming capability with collaborative combat aircraft or "loyal wingmen", and cockpit improvements. To preserve the aircraft's stealth while enabling additional payload and fuel capacity, stealthy external carriage has been investigated since the mid-2000s, with a low drag, low-observable 600-gallon external tank and pylon currently under development. The planned Multifunction Advanced Data Link (MADL) integration was cut due to development delays and lack of proliferation among USAF platforms. Although the Thales Scorpion helmet-mounted cuing system (HMCS) was successfully tested on the F-22 in 2013, funding cuts prevented its deployment. Lockheed Martin has proposed upgrading all Block 20 training aircraft to Block 30/35 in order to increase numbers available for combat. The F-22 has also been used to test technology for its eventual successor from the Next Generation Air Dominance (NGAD) program; some advances are expected to be applied to the F-22 as well.

Aside from capability upgrades, the F-22 fleet underwent a \$350 million "structures retrofit program" to address improper titanium heat treatment in the parts of certain airframe batches. By January 2021, all aircraft had gone through the Structural Repair Program to ensure full lifetimes for all aircraft. In the long term, the F-22 is expected to eventually be succeeded by the NGAD's crewed fighter component.

## Design

### Overview

The F-22 Raptor is a fifth-generation air superiority fighter that is considered fourth generation in stealth aircraft technology by the USAF. It is the first operational aircraft to combine supercruise, supermaneuverability, stealth, and sensor fusion in a single weapons platform to enable it to conduct missions, primarily counter-air operations, in highly contested environments.

The F-22's shape combines stealth and aerodynamic performance. Planform and panel edges are aligned and surfaces have continuous curvature to minimize its radar cross-section. Its clipped diamond-like delta wings are smoothly blended into the angular fuselage with four empennage surfaces and leading edge root extensions running to the upper outboard corner of the caret inlets; the inlet upper edges also meet the fuselage's forebody chines. Flight control surfaces include leading-edge flaps, flaperons, ailerons, rudders on the canted vertical stabilizers, and all-moving horizontal tails (stabilators); for speed brake function, the ailerons deflect up, flaperons down, and rudders outwards to increase drag. Owing to the focus on supersonic performance, extensive area-ruling is applied to the airplane's shape and nearly all of the fuselage volume lies ahead of the wing's trailing edge, with the stabilators pivoting from tail booms extending aft of the engine nozzles. Weapons are carried internally in the fuselage for stealth. The aircraft has a refueling boom receptacle centered on its spine and retractable tricycle landing gear as well as an emergency tailhook; fire suppression system and fuel tank inerting system are installed for survivability.

The aircraft's dual Pratt & Whitney F119 augmented turbofan engines are closely spaced and incorporate pitch-axis thrust vectoring nozzles with a range of ±20 degrees; the nozzles are fully integrated into the F-22's flight controls and vehicle management system. Each engine has maximum thrust in the 35,000 lbf (156 kN) class. The F-22's thrust-to-weight ratio at typical combat weight is nearly at unity in maximum military power and 1.25 in full afterburner. The caret inlets are offset from the forward fuselage to divert the boundary layer and generate oblique shocks with the upper inboard corners to ensure good total pressure recovery and efficient supersonic flow compression. Maximum speed without external stores is approximately Mach 1.8 at military power and greater than Mach 2 with afterburners. With 18,000 lb (8,165 kg) of internal fuel and an additional 8,000 lb (3,629 kg) in two 600-gallon external tanks, the jet has a ferry range of over 1,600 nmi (1,840 mi; 2,960 km).

The F-22's high cruise speed and operating altitude over prior fighters improve the effectiveness of its sensors and weapon systems, and increase survivability against ground defenses such as surface-to-air missiles. The ability to supercruise, or sustain supersonic flight without using afterburners, allows it to intercept targets that afterburner-dependent aircraft would lack the fuel to reach. The use of internal weapons bays permits the aircraft to maintain comparatively higher performance over most other combat-configured fighters due to a lack of parasitic drag from external stores. The F-22's thrust and aerodynamics enable regular combat speeds of Mach 1.5 at 50,000 feet (15,000 m), thus providing 50% greater employment range for air-to-air missiles and twice the effective range for JDAMs than with prior platforms. Its structure contains a significant amount of high-strength materials to withstand stress and heat of sustained supersonic flight. Respectively, titanium alloys and bismaleimide/epoxy composites comprise 42% and 24% of the structural weight.

The airplane's aerodynamics, relaxed stability, and powerful thrust-vectoring engines give it excellent maneuverability and energy potential across its flight envelope. Its large control surfaces, vortex-generating chines and LERX, and vectoring nozzles provide excellent high alpha (angle of attack) characteristics, and is capable of flying at trimmed alpha of over 60° while maintaining roll control and performing maneuvers such as the Herbst maneuver (J-turn) and Pugachev's Cobra. The triplex-redundant fly-by-wire control system and full-authority digital engine control (FADEC) make the aircraft highly departure resistant and controllable, thus giving the pilot carefree handling.

### Stealth

The F-22 was designed to be highly difficult to detect and track by radar, with radio waves reflected, scattered, or diffracted away from the emitter source towards specific sectors, or absorbed and attenuated. Measures to reduce RCS include airframe shaping such as alignment of edges and continuous curvature of surfaces, internal carriage of weapons, fixed-geometry serpentine inlets and curved vanes that prevent line-of-sight of the engine faces and turbines from any exterior view, use of radar-absorbent material (RAM), and attention to detail such as hinges and pilot helmets that could provide a radar return. The F-22 was also designed to have decreased radio frequency emissions, infrared signature and acoustic signature as well as reduced visibility to the naked eye. The aircraft's flat thrust-vectoring nozzles reduce infrared emissions of the exhaust plume to mitigate the threat of infrared homing ("heat seeking") surface-to-air or air-to-air missiles. Additional measures to reduce the infrared signature include special topcoat and active cooling to manage the heat buildup from supersonic flight.

Compared to previous stealth designs like the F-117, the F-22 is less reliant on RAM, which are maintenance-intensive and susceptible to adverse weather conditions. Unlike the B-2, which requires climate-controlled hangars, the F-22 can undergo repairs on the flight line or in a normal hangar. The F-22 incorporates a Signature Assessment System which delivers warnings when the radar signature is degraded and necessitates repair. While the F-22's exact RCS is classified, in 2009 Lockheed Martin released information indicating that from certain angles the airplane has an RCS of 0.0001 m<sup>2</sup> or −40 dBsm – equivalent to the radar reflection of a "steel marble"; the aircraft can mount a Luneburg lens reflector to mask its RCS. Effectively maintaining the stealth features can decrease the F-22's mission capable rate to 62–70%.

The effectiveness of the stealth characteristics is difficult to gauge. The RCS value is a restrictive measurement of the aircraft's frontal or side area from the perspective of a static radar. When an aircraft maneuvers it exposes a completely different set of angles and surface area, potentially increasing radar observability. Furthermore, the F-22's stealth contouring and radar-absorbent materials are chiefly effective against high-frequency radars, usually found on other aircraft. The effects of Rayleigh scattering and resonance mean that low-frequency radars such as weather radars and early-warning radars are more likely to detect the F-22 due to its physical size. These are also conspicuous, susceptible to clutter, and have low precision. Additionally, while faint or fleeting radar contacts make defenders aware that a stealth aircraft is present, reliably vectoring interception to attack the aircraft is much more challenging. According to the USAF an F-22 surprised an Iranian F-4 Phantom II that was attempting to intercept an American UAV, despite Iran's assertion of having military VHF radar coverage over the Persian Gulf.

Beginning in 2021, the F-22 has been seen testing a new chrome-like surface coating. This highly polished surface appears to change color based on the viewer's orientation to the aircraft. It is speculated that the new coating will help to reduce the F-22's detectability by IRST and other infrared tracking systems and missiles. This coating has also been seen on some F-35 and F-117 test aircraft.

### Avionics

The aircraft has an integrated avionics system where through sensor fusion, data from all onboard sensor systems as well as off-board inputs are filtered and processed into a combined tactical picture, thus enhancing the pilot's situational awareness and reducing workload. Key mission systems include Sanders/General Electric AN/ALR-94 electronic warfare system, Martin Marietta AN/AAR-56 infrared and ultraviolet Missile Launch Detector (MLD), Westinghouse/Texas Instruments AN/APG-77 active electronically scanned array (AESA) radar, TRW Communication/Navigation/Identification (CNI) suite, and long range advanced IRST currently being tested. The F-22's baseline software has some 1.7 million lines of code, the majority involving the mission systems such as processing radar data. The integrated nature of the avionics, as well as the use of Ada, has made the development and testing of upgrades challenging. To enable more rapid upgrades, the avionics suite added an open mission systems (OMS) processor, as well as an open-source Kubernetes platform called the Open Systems Enclave (OSE) to enable the use of containerized software from third-party vendors.

The APG-77 radar has a low-observable, active-aperture, electronically scanned antenna with multiple target track-while-scan in all weather conditions; the antenna is tilted back for stealth. Its emissions can be focused to overload enemy sensors as an electronic-attack capability. The radar changes frequencies more than 1,000 times per second to lower interception probability and has an estimated range of 125–150 mi (201–241 km) against an 11 sq ft (1 m<sup>2</sup>) target and 250 mi (400 km) or more in narrow beams. The upgraded APG-77(V)1 provides air-to-ground functionality through synthetic aperture radar (SAR) mapping, ground moving target indication/track (GMTI/GMTT), and strike modes. Alongside the radar is the ALR-94 electronic warfare system, among the most technically complex equipment on the F-22, that integrates more than 30 antennas blended into the wings and fuselage for all-round radar warning receiver (RWR) coverage and threat geolocation. It can be used as a passive detector capable of searching targets at ranges (250+ nmi) exceeding the radar's, and can provide enough information for a radar lock and cue emissions to a narrow beam (down to 2° by 2° in azimuth and elevation). Depending on the detected threat, the defensive systems can prompt the pilot to release countermeasures such as flares or chaff. The MLD uses six sensors to provide full spherical infrared coverage while the advanced IRST, housed in a stealthy wing pod, is a narrow field-of-view sensor for long-range passive identification and targeting. To ensure stealth in the radio frequency spectrum, CNI emissions are strictly controlled and confined to specific sectors, with tactical communication between F-22s performed using the directional Inter/Intra-Flight Data Link (IFDL); the integrated CNI system also manages TACAN, IFF (including Mode 5 through the MIDS-JTRS terminal), and communication through HAVE QUICK/SATURN and SINCGARS. Radar and CNI information are processed by two Hughes Common Integrated Processor (CIP)s, each capable of processing up to 10.5 billion instructions per second. The aircraft has also been upgraded to incorporate an automatic ground collision avoidance system (GCAS).

The F-22's ability to operate close to the battlefield gives the aircraft threat detection and identification capability comparative with the RC-135 Rivet Joint, and the ability to function as a "mini-AWACS", though its radar is less powerful than those of dedicated platforms. This allows the F-22 to rapidly designate targets for allies and coordinate friendly aircraft. Data can be transferred to other aircraft through a BACN or via Link 16 through MIDS-JTRS. The IEEE 1394B bus developed for the F-22 was derived from the commercial IEEE 1394 "FireWire" bus system. In 2007, the F-22's radar was tested as a wireless data transceiver, transmitting data at 548 megabits per second and receiving at gigabit speed, far faster than the Link 16 system. The radio frequency receivers of the electronic support measures (ESM) system give the aircraft the ability to perform intelligence, surveillance, and reconnaissance (ISR) tasks.

### Cockpit

The F-22 has a glass cockpit with all-digital flight instruments. The monochrome head-up display offers a wide field of view and serves as a primary flight instrument; information is also displayed upon six color liquid-crystal display (LCD) panels. The primary flight controls are a force-sensitive side-stick controller and a pair of throttles. The USAF initially wanted to implement direct voice input (DVI) controls, but this was judged to be too technically risky and was abandoned. The canopy's dimensions are approximately 140 inches long, 45 inches wide, and 27 inches tall (355 cm × 115 cm × 69 cm) and weighs 360 pounds. The canopy was redesigned after the original design lasted an average of 331 hours instead of the required 800 hours.

The F-22 has integrated radio functionality, the signal processing systems are virtualized rather than as a separate hardware module. The integrated control panel (ICP) is a keypad system for entering communications, navigation, and autopilot data. Two 3 in × 4 in (7.6 cm × 10.2 cm) up-front displays located around the ICP are used to display integrated caution advisory/warning (ICAW) data, CNI data and also serve as the stand-by flight instrumentation group and fuel quantity indicator for redundancy. The stand-by flight group displays an artificial horizon, for basic instrument meteorological conditions. The 8 in × 8 in (20 cm × 20 cm) primary multi-function display (PMFD) is located under the ICP, and is used for navigation and situation assessment. Three 6.25 in × 6.25 in (15.9 cm × 15.9 cm) secondary multi-function displays are located around the PMFD for tactical information and stores management.

The ejection seat is a version of the ACES II commonly used in USAF aircraft, with a center-mounted ejection control. The F-22 has a complex life support system, which includes the onboard oxygen generation system (OBOGS), protective pilot garments, and a breathing regulator/anti-g (BRAG) valve controlling flow and pressure to the pilot's mask and garments. The pilot garments were developed under the Advanced Technology Anti-G Suit (ATAGS) project and protect against chemical/biological hazards and cold-water immersion, counter g-forces and low pressure at high altitudes, and provide thermal relief. Following a series of hypoxia-related issues, the life support system was consequently revised to include an automatic backup oxygen system and a new flight vest valve. In combat environments, the ejection seat includes a modified M4 carbine designated the GAU-5/A.

### Armament

The F-22 has three internal weapons bays: a large main bay on the bottom of the fuselage, and two smaller bays on the sides of the fuselage, aft of the engine inlets; a small bay for countermeasures such as flares is located behind each side bay. The main bay is split along the centerline and can accommodate six LAU-142/A launchers for beyond-visual-range (BVR) missiles and each side bay has an LAU-141/A launcher for short-range missiles. The primary air-to-air missiles are the AIM-120 AMRAAM and the AIM-9 Sidewinder, with planned integration of the AIM-260 JATM. Missile launches require the bay doors to be open for less than a second, during which pneumatic or hydraulic arms push missiles clear of the aircraft; this is to reduce vulnerability to detection and to deploy missiles during high-speed flight. An internally mounted M61A2 Vulcan 20 mm rotary cannon is embedded in the airplane's right wing root with the muzzle covered by a retractable door. The radar projection of the cannon fire's path is displayed on the pilot's head-up display.

Although designed for air-to-air missiles, the main bay can replace four launchers with two bomb racks that can each carry one 1,000 lb (450 kg) or four 250 lb (110 kg) bombs for a total of 2,000 pounds (910 kg) of air-to-surface ordnance. While capable of carrying weapons with GPS guidance such as JDAMs and SDBs, the F-22 cannot self-designate laser-guided weapons.

While the F-22 typically carries weapons internally, the wings include four hardpoints, each rated to handle 5,000 lb (2,300 kg). Each hardpoint can accommodate a pylon that can carry a detachable 600-gallon (2,270 L) external fuel tank or a launcher holding two air-to-air missiles; the two inboard hardpoints are "plumbed" for external fuel tanks. The two outboard hardpoints have since been dedicated to a pair of stealthy pods housing the IRST and mission systems. The aircraft can jettison external tanks and their pylon attachments to restore its low observable characteristics and kinematic performance.

### Maintenance

Each airplane requires a three-week packaged maintenance plan (PMP) every 300 flight hours. The stealth coatings of the F-22 were designed to be more robust and weather-resistant than those used in earlier stealth aircraft. However, early coatings failed against rain and moisture when F-22s were initially posted to Guam in 2009. The stealth system account for almost one third of maintenance, with coatings being particularly demanding; more durable coatings are being developed in order to reduce maintenance efforts. F-22 depot maintenance is performed at Ogden Air Logistics Complex at Hill AFB, Utah, and considerable care is taken during maintenance due to the limited attrition reserve aircraft numbers of the small fleet size.

F-22s were available for missions 63% of the time on average in 2015, up from 40% when the aircraft was introduced in 2005. Maintenance hours per flight hour was also improved from 30 early on to 10.5 by 2009, lower than the requirement of 12; man-hours per flight hour was 43 in 2014. When introduced, the F-22 had a Mean Time Between Maintenance (MTBM) of 1.7 hours, short of the required 3.0; this rose to 3.2 hours in 2012. By fiscal year 2015, the cost per flight hour was \$59,116.

## Operational history

### Designation and testing

The YF-22 was originally given the unofficial name "Lightning II", from the World War II Lockheed P-38 Lightning fighter which persisted until the mid-1990s, when the USAF officially named the F-22 "Raptor". The "Lightning II" name was later given to the F-35. The aircraft was also briefly dubbed "SuperStar" and "Rapier". In September 2002, USAF changed the Raptor's designation to F/A-22, mimicking the Navy's McDonnell Douglas F/A-18 Hornet and intended to highlight a planned ground-attack capability amid debate over the aircraft's role and relevance. The F-22 designation was reinstated in December 2005, when the aircraft entered service.

The F-22 flight test program consisted of flight sciences, developmental test (DT), and initial operational test and evaluation (IOT&E) by the 411th Flight Test Squadron at Edwards AFB, California, as well as follow-on OT&E and development of tactics and operational employment by the 422nd Test and Evaluation Squadron at Nellis AFB, Nevada. Flight testing began in 1997 with Raptor 4001, the first EMD F-22, and eight more EMD jets assigned to the 411th FLTS would participate in the test program under the Combined Test Force (CTF) at Edwards. The first two aircraft conducted envelope expansion testing such as flying qualities, air vehicle performance, propulsion, and stores separation. The third aircraft, the first to have production-level internal structure, tested flight loads, flutter, and JDAM separation, while two non-flying F-22s were built for testing static loads and fatigue. Subsequent EMD aircraft and the Boeing 757 FTB tested avionics, CNI, environmental qualifications, and observables, with the first combat-capable Block 3.0 software flying in 2001. Raptor 4001 was retired from flight testing in 2000 and subsequently sent to Wright-Patterson AFB for survivability testing, including live fire testing and battle damage repair training. Other retired EMD F-22s have been used as maintenance trainers.

The F-22's numerous technological leaps required extensive testing that would result in repeated delays. While the first production aircraft was delivered to Edwards in October 2002 for IOT&E and the first aircraft for the 422nd TES at Nellis arrived in January 2003, IOT&E was pushed back from its planned start in mid-2003, with avionics stability being particularly challenging. Following a preliminary assessment, called OT&E Phase 1, formal IOT&E began in April 2004 and was completed in December of that year. This marked the successful demonstration of the jet's air-to-air mission capability, although it was also more maintenance intensive than expected. A Follow-On OT&E (FOT&E) in 2005 cleared the F-22's air-to-ground mission capability. Delivery of operational aircraft for pilot training at Tyndall AFB, Florida began in September 2003, and the first combat ready F-22 of the 1st Fighter Wing arrived at Langley AFB, Virginia in January 2005. As the F-22 was designed for upgrades throughout its lifecycle, the 411th FLTS and 422nd TES would continue the DT/OT&E and tactics development of these upgrades. The 411th FLTS' fleet was further augmented by a dedicated Block 30 test aircraft in 2010.

In August 2008, an unmodified F-22 of the 411th FLTS performed the first ever air-to-air refueling of an aircraft using synthetic jet fuel as part of a wider USAF effort to qualify aircraft to use the fuel, a 50/50 mix of JP-8 and a Fischer–Tropsch process-produced, natural gas-based fuel. In 2011, an F-22 flew supersonic on a 50% mixture of biofuel derived from camelina.

### Training

The 43rd Fighter Squadron was reactivated in 2002 as the F-22 Formal Training Unit (FTU) for the type's basic course at Tyndall AFB. Following severe damage to the installation in the wake of Hurricane Michael in 2018, the squadron and its aircraft were relocated to nearby Eglin AFB; the storm had also damaged several F-22s, which were later repaired. The FTU and its aircraft were reassigned to the 71st Fighter Squadron at Langley AFB in 2023. To reduce operating costs and prolong the F-22's service life, some pilot training sorties are performed using flight simulators, while the T-38 Talon is used for adversary training. The advanced F-22 weapons instructor course at USAF Weapons School is conducted by the 433rd Weapons Squadron at Nellis AFB.

### Introduction into service

In December 2005, the USAF announced that the F-22 had achieved Initial Operational Capability (IOC) with the 94th Fighter Squadron. The unit subsequently participated in Exercise Northern Edge in Alaska in June 2006 and Exercise Red Flag 07–1 at Nellis AFB in February 2007, where it demonstrated the F-22's greatly increased air combat capabilities when flying against Red Force Aggressor F-15s and F-16s and also refined operational tactics and employment.

The F-22 achieved Full Operational Capability (FOC) in December 2007, when General John Corley of Air Combat Command (ACC) officially declared the F-22s of the integrated active duty 1st Fighter Wing and Virginia Air National Guard 192d Fighter Wing fully operational. This was followed by an Operational Readiness Inspection (ORI) of the integrated wing in April 2008, in which it was rated "excellent" in all categories, with a simulated kill-ratio of 221–0.

### Initial operational problems

During the initial years of service, F-22 pilots experienced symptoms as a result of oxygen system issues that include loss of consciousness, memory loss, emotional lability and neurological changes as well as lingering respiratory problems and a chronic cough; the issues resulted in a four-month grounding in 2011. In August 2012, the DoD found that the BRAG valve, used to inflate the pilot's vest during high-g maneuvers, was defective and restricted breathing and the OBOGS (onboard oxygen generation system) unexpectedly reduced oxygen levels during high-g maneuvers. The Raptor Aeromedical Working Group had recommended several changes in 2005 regarding oxygen supply issues that were initially unfunded but received further consideration in 2012. The F-22 CTF and 412th Aerospace Medicine Squadron eventually determined that breathing restrictions were the root cause. The coughing symptoms were attributed to acceleration atelectasis from high g exposure and the OBOGS delivering excessive oxygen concentration at low altitudes. The presence of toxins and particles in some ground crew was deemed to be unrelated. Modifications to the life-support equipment and oxygen system allowed the distance and altitude flight restrictions to be lifted on 4 April 2013.

### Operational service

Following IOC and large-scale exercises, the F-22 flew its first homeland defense mission in January 2007. In November 2007, F-22s of 90th Fighter Squadron at Elmendorf AFB, Alaska, performed their first North American Aerospace Defense Command (NORAD) interception of two Russian Tu-95MS bombers. Since then, F-22s have also escorted probing Tu-160 bombers.

The F-22 was first deployed overseas in February 2007 with the 27th Fighter Squadron to Kadena Air Base in Okinawa, Japan. This first overseas deployment was initially marred by problems when six F-22s flying from Hickam AFB, Hawaii, experienced multiple software-related system failures while crossing the International Date Line (180th meridian of longitude). The aircraft returned to Hawaii by following tanker aircraft. Within 48 hours, the error was resolved and the journey resumed. Kadena would be a frequent rotation for F-22 units; they have also been involved in training exercises in South Korea and Malaysia.

Defense Secretary Gates initially refused to deploy F-22s to the Middle East in 2007; the type made its first deployment in the region at Al Dhafra Air Base in the UAE in 2009. In April 2012, F-22s have been rotating into Al Dhafra, less than 200 miles from Iran. In March 2013, the USAF announced that an F-22 had intercepted an Iranian F-4 Phantom II that approached within 16 miles of an MQ-1 Predator flying off the Iranian coastline.

On 22 September 2014, F-22s performed the type's first combat sorties by conducting some of the opening strikes of Operation Inherent Resolve, the American-led intervention in Syria; aircraft dropped 1,000-pound GPS-guided bombs on Islamic State targets near Tishrin Dam. Between September 2014 and July 2015, F-22s flew 204 sorties over Syria, dropping 270 bombs at some 60 locations. Throughout their deployment, F-22s conducted close air support (CAS) and also deterred Syrian, Iranian, and Russian aircraft from attacking U.S.-backed Kurdish forces and disrupting U.S. operations in the region. F-22s also participated in the U.S. strikes that defeated pro-government and Russian Wagner Group paramilitary forces near Khasham in eastern Syria on 7 February 2018. These strikes notwithstanding, the F-22's main role in the operation was conducting intelligence, surveillance and reconnaissance.

In late 2014, the USAF tested a rapid deployment concept involving four F-22s and one C-17 for support, first proposed in 2008 by two F-22 pilots. The goal was for the type to be able to set up and engage in combat within 24 hours. Four F-22s were deployed to Spangdahlem Air Base in Germany in August, Łask Air Base in Poland, and Ämari Air Base in Estonia in September 2015, to train with NATO allies.

In November 2017, F-22s operating alongside B-52s bombed opium production and storage facilities in Taliban-controlled regions of Afghanistan. In 2019, the F-22 cost US\$35,000 per flight hour to operate.

On 4 February 2023, an F-22 of the 1st Fighter Wing shot down an alleged Chinese spy balloon within visual range off the coast of South Carolina at an altitude of 60,000 to 65,000 ft. The wreckage landed approximately 6 miles offshore and was subsequently secured by ships of the U.S. Navy and U.S. Coast Guard. F-22s shot down additional high-altitude objects near the coast of Alaska on 10 February and over Yukon on 11 February.

## Variants

YF-22A
Pre-production technology demonstrator for Advanced Tactical Fighter (ATF) demonstration/validation phase; two were built.

F-22A
Single-seat version, was designated F/A-22A in early 2000s; 195 built, consisting of 8 test and 187 production aircraft.

F-22B
Planned two-seat version, cancelled in 1996 to save development costs with test aircraft orders converted to F-22A.

Naval F-22 variant
Planned carrier-borne variant of the F-22 with variable-sweep wings for the U.S. Navy's Navy Advanced Tactical Fighter (NATF) program to replace the F-14 Tomcat. Program was cancelled in 1991.

### Proposed derivatives

The FB-22 was a proposed medium-range supersonic stealth bomber for the USAF. The design was projected to carry up to 30 Small Diameter Bombs to about twice the range of the F-22A. The FB-22 proposals were cancelled with the 2006 Quadrennial Defense Review and subsequent developments, in lieu of a larger subsonic bomber with a much greater range.

The X-44 MANTA, or multi-axis, no-tail aircraft, was a planned experimental aircraft based on the F-22 with enhanced thrust vectoring controls and no aerodynamic surface backup. The aircraft was to be solely controlled by thrust vectoring, without featuring any rudders, ailerons, or elevators. Funding for this program was halted in 2000.

In August 2018, Lockheed Martin proposed an F-22 derivative to the USAF and JASDF that would combine an improved and modified F-22 airframe with the avionics and improved stealth coatings of the F-35. The proposal was not considered by the USAF or JASDF due to cost as well as existing export restrictions.

## Operators

The United States Air Force is the only operator of the F-22. As of August 2022, it has 183 aircraft in its inventory.

### Air Combat Command

- 1st Fighter Wing - Joint Base Langley–Eustis, Virginia
  - 27th Fighter Squadron
  - 71st Fighter Squadron (Formal Training Unit)
  - 94th Fighter Squadron
- 49th Wing - Holloman Air Force Base, New Mexico
  - 7th Fighter Squadron
  - 8th Fighter Squadron
- 53d Wing - Eglin Air Force Base, Florida
  - 422d Test and Evaluation Squadron
- 57th Wing - Nellis Air Force Base, Nevada
  - 433d Weapons Squadron
- 325th Fighter Wing - Tyndall Air Force Base, Florida
  - 43d Fighter Squadron - Eglin Air Force Base, Florida
  - 95th Fighter Squadron

### Pacific Air Forces

- 3rd Wing - Joint Base Elmendorf–Richardson, Alaska
  - 90th Fighter Squadron
  - 525th Fighter Squadron
- 15th Wing - Hickam Air Force Base, Hawaii
  - 19th Fighter Squadron (active associate unit)

### Air National Guard

- 154th Wing - Hickam Air Force Base, Hawaii
  - 199th Fighter Squadron
- 192d Fighter Wing - Joint Base Langley–Eustis, Virginia
  - 149th Fighter Squadron (associate unit)

### Air Force Reserve Command

- 477th Fighter Group – Joint Base Elmendorf–Richardson, Alaska
  - 302d Fighter Squadron (associate unit)i

### Air Force Material Command

- 412th Test Wing - Edwards Air Force Base, California
  - 411th Flight Test Squadron

## Accidents

The first F-22 crash occurred during takeoff at Nellis AFB on 20 December 2004, in which the pilot ejected safely before impact. The investigation revealed that a brief interruption in power during an engine shutdown prior to flight caused a flight-control system malfunction; consequently the aircraft design was corrected to avoid the problem. Following a brief grounding, F-22 operations resumed after a review.

On 25 March 2009, an EMD F-22 crashed 35 miles (56 km) northeast of Edwards AFB during a test flight, resulting in the death of Lockheed Martin test pilot David P. Cooley. An Air Force Materiel Command investigation found that Cooley momentarily lost consciousness during a high-G maneuver, or g-LOC, then ejected when he found himself too low to recover. Cooley was killed during ejection by blunt-force trauma from windblast due to the aircraft's speed. The investigation found no design issues.

On 16 November 2010, an F-22 from Elmendorf AFB crashed, killing the pilot, Captain Jeffrey Haney. F-22s were restricted to flying below 25,000 feet, then grounded during the investigation. The crash was attributed to a bleed air system malfunction after an engine overheat condition was detected, shutting down the Environmental Control System (ECS) and OBOGS. The accident review board ruled Haney was to blame, as he did not react properly to engage the emergency oxygen system. Haney's widow sued Lockheed Martin, claiming equipment defects, and later reached a settlement. After the ruling, the emergency oxygen system engagement handle was redesigned; the system was eventually replaced by an automatic backup oxygen system (ABOS). On 11 February 2013, the DoD's Inspector General released a report stating that the USAF had erred in blaming Haney, and that facts did not sufficiently support conclusions; the USAF stated that it stood by the ruling.

During a training mission, an F-22 crashed to the east of Tyndall AFB, on 15 November 2012. The pilot ejected safely and no injuries were reported on the ground. The investigation determined that a "chafed" electrical wire ignited the fluid in a hydraulic line, causing a fire that damaged the flight controls.

On 15 May 2020, an F-22 from Eglin Air Force Base crashed during a routine training mission shortly after takeoff; the pilot ejected safely. The cause of the crash was attributed to a maintenance error after an aircraft wash resulting in faulty air data sensor readings.

## Aircraft on display

- 91-4002 – Hill Air Force Base Aerospace Museum in Ogden, Utah
- 91-4003 – National Museum of the United States Air Force in Dayton, Ohio

## Specifications (F-22A)

## See also

American air superiority fighter by Lockheed Martin


Demographic history of Scotland

The demographic history of Scotland includes all aspects of population history in what is now Scotland. Scotland may have been first occupied in the last interglacial period (130,000–70,000 BC), but the earliest surviving archaeological evidence of human settlement is of Mesolithic hunter-gatherer encampments. These suggest a highly mobile boat-using people, probably with a very low density of population. Neolithic farming brought permanent settlements dating from 3500 BC, and greater concentrations of population. Evidence of hillforts and other buildings suggest a growing settled population. Changes in the scale of woodland indicates that the Roman invasions from the first century AD had a negative impact on the native population.

There are almost no written sources from which to reconstruct the demography of early medieval Scotland. This was probably a high fertility, high mortality society, similar to developing countries in the modern world. The population may have grown from half a million to a million by the mid-fourteenth century when the Black Death reached the country. It may then have fallen to as low as half a million by the end of the fifteenth century. Roughly half lived north of the River Tay and perhaps 10 per cent in the burghs that grew up in the later medieval period. Inflation in prices, indicating greater demand, suggests that the population continued to grow until the late sixteenth century, when it probably levelled off. It began to grow again in the relative stability of the late seventeenth century. The earliest reliable evidence suggests a population of 1.2 million in 1681. This was probably reduced by the "seven ill years" of the 1690s, which caused severe famine and depopulation, particularly in the north. The first national census was conducted in 1755, and showed the population of Scotland as 1,265,380. By then four towns had populations of over 10,000, with the capital, Edinburgh, the largest with 57,000 inhabitants.

Overall the population of Scotland grew rapidly in the late eighteenth and nineteenth centuries. Whilst the Lowland Clearances caused depopulation in the affected areas, only local net population reductions occurred in the Highlands during the Highland Clearances. By 1801, Scotland's population had reached 1,608,420 and it grew to 2,889,000 in 1851 and 4,472,000 in 1901. By the beginning of the twentieth century, one in three lived in the four cities of Glasgow, Edinburgh, Dundee and Aberdeen. Glasgow emerged as the largest city, with a population of 762,000 by 1901, making it "the Second City of the Empire". Despite industrial expansion there were insufficient jobs and between the mid-nineteenth century and the Great Depression about two million Scots emigrated to North America and Australia, and another 750,000 to England. The Scots were only 10 per cent of the British population but they provided 15 per cent of the national armed forces, and eventually accounted for 20 per cent of the dead in World War I (1914–18). With the end of mass migration, the population reached a peak of 5,240,800 in 1974. Thereafter it began to fall slowly, moving down to 5,062,940 in 2000. There was also a decrease in some urban populations as a result of policies of slum clearance, overspill and relocation to new towns, with the population of Glasgow falling from over a million in 1951 to 629,000 in 2001. Rural areas also saw a loss of population, particularly in the Highlands and Hebrides.

## Prehistoric and Roman eras

At times during the last interglacial period (130,000– 70,000 BC) Europe had a climate warmer than today's, and early humans may have made their way to what is now Scotland, though archaeologists have found no traces of this. Glaciers then scoured their way across most of Britain, and only after the ice retreated did Scotland again become habitable, around 9600 BC. Mesolithic hunter-gatherer encampments formed the first known settlements, and archaeologists have dated a site near Biggar to around 8500 BC. Numerous other sites found around Scotland build up a picture of highly mobile boat-using people making tools from bone, stone and antlers, probably with a very low density of population.

Neolithic farming brought permanent settlements, such as the stone house at Knap of Howar on Papa Westray dating from 3500 BC, and greater concentrations of population. Although the Roman geographer Ptolemy indicated that there were 19 "towns" in Caledonia, north of the Roman province of Britannia, no clear evidence of urban settlements has been found and these were probably hillforts. There is evidence of over 1,000 such forts, most south of the Clyde-Forth line, but the majority seem to have been abandoned in the Roman period. There is also evidence of distinctive stone wheelhouses (a type of roundhouse, with a circle of stone piers resembling the spokes of a wheel) and over 400 small underground souterrains (underground galleries that may have been used to store food). Extensive analyses of Black Loch in Fife indicate that arable land spread at the expense of forest from about 2000 BCuntil the time of the Roman advance into lowland Scotland in the first century AD, suggesting an expanding settled population. Thereafter, there was regrowth of birch, oak and hazel for some 500 years, suggesting that the Roman invasions had a negative impact on the native population.

## Middle Ages

There are almost no written sources from which to reconstruct the demography of early medieval Scotland. Estimates have been made of a population of 10,000 in Dál Riata and 80–100,000 for Pictland, which was probably the largest region. It is likely that the fifth and sixth centuries saw higher mortality rates due to the appearance of bubonic plague, which may have reduced the population. The examination of burial sites for this period, such as that at Hallowhill, St Andrews, indicates a life expectancy of only 26 to 29. The known conditions have been taken to suggest it was a high fertility, high mortality society, similar to developing countries in the modern world, with a relatively young demographic profile, and perhaps early childbearing, and large numbers of children born to each woman (although with high child mortality). This would have meant a relatively low ratio of available workers to the number of mouths to feed, which in turn would have made it difficult to produce a surplus that would allow demographic growth and the development of more complex societies.

From the formation of the Kingdom of Alba in the tenth century, to before the Black Death reached the country in 1349, estimates based on the amount of farmable land suggest that the population may have grown from half a million to a million. Growth was probably punctuated by occasional crises, like the famines recorded in chronicles for 1154 and 1256. More significant was a series of poor harvests that affected Scotland and most of Europe in the early fourteenth century and widespread famines in 1315–16 and in the later 1330s.

Although there is no reliable documentation of the demographic impact of the Black Death in Scotland, there are some indications of the immediate effects of the plague. Walter Bower recorded that 24, about a third, of the canons of St. Andrews died during the outbreak. There are also anecdotal references to abandoned land in the following decades. If the pattern followed that in England, then the population may have fallen to as low as half a million by the end of the fifteenth century. Compared with the distribution of population after the later Clearances and the Industrial Revolution, these numbers would have been relatively evenly spread over the kingdom, with roughly half living north of the River Tay.

## Early modern era

Price inflation, which generally reflects growing demand for food, suggests that the population was probably still expanding in the first half of the sixteenth century. Almost half the years in the second half of the sixteenth century saw local or national scarcity, necessitating the shipping of large quantities of grain from the Baltic. Distress was exacerbated by outbreaks of plague, with major epidemics in the periods 1584-8, 1595 and 1597–1609. The population expansion probably levelled off after the famine of the 1590s, as prices were relatively stable in the early seventeenth century. Famine was common, with four periods of famine prices between 1620 and 1625. The invasions of the 1640s had a profound impact on the Scottish economy, with the destruction of crops and the disruption of markets resulting in some of the most rapid price rises of the century, but population probably expanded in the Lowlands in the period of stability that followed the Restoration in 1660. There is evidence that there was a different demographic regime operating in the Highlands, where growth probably continued from the early seventeenth century to the late eighteenth century.

Estimates based on hearth tax returns for 1691 indicate a population of around 1.2 million. The population may have been seriously affected by the failed harvests (1695, 1696 and 1698-9) known as the "seven ill years". The result was severe famine and depopulation, particularly in the north. Starvation probably killed 5 to 15 per cent of the Scottish population, but in areas like Aberdeenshire death rates reached 25 per cent. The famines of the 1690s were seen as particularly severe, partly because famine had become relatively rare in the second half of the seventeenth century, with only one year of dearth (in 1674), and the shortages of the 1690s were the last of their kind. Between 1650 and 1700 approximately 7,000 Scots migrated to America, 10–20,000 to Europe and England and 60–100,000 to Ireland. The first reliable figure for the national population is from the census conducted by the Reverend Alexander Webster in 1755, which showed the inhabitants of Scotland as 1,265,380 persons.

Unlike in England, where the nucleated village existed relatively early, most of the early modern population of Scotland, in both the Lowlands and Highlands, was housed in small clachans or townships and isolated dwellings. These were unstructured groups of houses, often belonging to between four and six tenants, who were often engaged in common agriculture. As the population expanded, some of these settlements were subdivided to create new clachans and more marginal land was settled, with sheilings (clusters of huts occupied while summer pasture was being used for grazing) becoming permanent settlements.

Perhaps 10 per cent of the population lived in the burghs that had grown up in the later medieval period, mainly in the east and south of the country. They perhaps had an average population of 2,000, but many were much smaller than 1,000, and the largest, Edinburgh, probably had a population of over 10,000 at the beginning of the period. Edinburgh doubled in size in the century after 1540, particularly after the plague of 1580, with most of its population probably coming from a growing reservoir in the surrounding countryside. It also expanded beyond the city walls in suburbs at Cowgate, Bristo and Westport and by 1750, with its suburbs, it had reached a population of 57,000. The only other towns above 10,000 by the end of the period were Glasgow with 32,000, Aberdeen with around 16,000 and Dundee with 12,000. By 1600 Scotland had a higher proportion of its population living in larger towns than contemporaneous Scandinavia, Switzerland and most of Eastern Europe: by 1750 in Europe, only Italy, the Low Countries and England were more urbanised than Scotland.

## Modern era

The agricultural revolution changed the traditional system of agriculture which had existed in Lowland Scotland. Thousands of cottars and tenant farmers migrated from farms and smallholdings to the new industrial centres of Glasgow, Edinburgh and northern England. Particularly after the end of the boom created by the Revolutionary and Napoleonic Wars (1790–1815), Highland landlords needed cash to maintain their position in London society. Whereas rents had often been paid in kind, the landlords turned to money rents. They evicted the farmers who had occupied run rig arable land and shared grazing. Their holdings were let to large scale sheep farmers, who could afford substantially higher rents. The eviction of tenants went against dùthchas, the principle that clan members had an inalienable right to rent land in the clan territory. Particularly in the north and west Highlands, estates offered alternative accommodation in newly established crofting communities, with the intention that the resettled tenants worked in fishing or the kelp industry. These evictions were the first phase of the Highland Clearances. The total population of the Highlands continued to rise throughout the clearances. The result was a continuous exodus from the land—to the cities, and further afield to England, Canada, America and Australia. The Great Famine of Ireland of the 1840s, caused by potato blight, which devastated the population of Ireland, reached the Highlands in 1846. The overcrowded crofting communities were highly dependent on the potato. Although 150,000 people faced disaster, they were rescued by an effective emergency relief system that stands in dramatic contrast to the failures of relief in Ireland and prevented a major demographic crisis.

By the time of the first decadal census in 1801, the population was 1,608,420. It grew steadily in the nineteenth century, to 2,889,000 in 1851 and 4,472,000 in 1901. While population fell in some rural areas, it rose rapidly in the towns. Aberdeen, Dundee and Glasgow grew by a third or more between 1755 and 1775 and the textile town of Paisley more than doubled its population. Because of the industrial revolution, Scotland was already one of the most urbanised societies in Europe by 1800. In 1800, 17 per cent of people in Scotland lived in towns of more than 10,000 inhabitants. By 1850 it was 32 per cent and by 1900 it was 50 per cent. By 1900 one in three of the entire population were in the four cities of Glasgow, Edinburgh, Dundee and Aberdeen. Glasgow emerged as the largest city. Its population in 1780 was 43,000, reaching 147,000 by 1820; by 1901 it had grown to 762,000. This was due to a high birth rate and immigration from the countryside and particularly from Ireland; but from the 1870s there was a fall in the birth rate and lower rates of migration and much of the growth was due to longer life expectancy. Glasgow was now one of the largest cities in the world, and it became known as "the Second City of the Empire" after London.

Mortality rates were high compared with England and other European nations. Evidence suggests a national death rate of 30 per 1,000 in 1755, 24 in the 1790s and 22 in the early 1860s. Mortality tended to be much higher in urban than rural settlements. The first time these were measured, 1861–82, in the four major cities these were 28.1 per 1,000 and 17.9 in rural areas. Mortality probably peaked in Glasgow in the 1840s, when large inflows of population from the Highlands and Ireland combined population outgrowing sanitary provision and combining with outbreaks of epidemic disease. National rates began to fall in the 1870s, particularly in the cities, as environmental conditions improved. By 1930–32 the national rate was 13.4 per 1,000, with a rate of 14.1 and in rural areas 12.8.

Even with the growth of industry there were not enough good jobs: as a result, from 1841 to 1931, about two million Scots emigrated to North America and Australia, and another 750,000 Scots relocated to England. With a population of 4.8 million in 1911, Scotland sent 690,000 men to the First World War, of whom 74,000 died in combat or from disease, and 150,000 were seriously wounded. Thus, although Scots were only 10 per cent of the British population, they made up 15 per cent of the national armed forces and eventually accounted for 8.3% of the UK's 887,858 dead from all causes. While emigration began to tail off in England and Wales after the First World War, it continued apace in Scotland, with 400,000 Scots, 10 per cent of the population, estimated to have left the country between 1921 and 1931. When the Great Depression hit in the 1930s there were no easily available jobs in the US and Canada, and emigration fell to less than 50,000 a year, bringing to an end the period of mass migrations that had opened in the mid-eighteenth century. This contributed to the growth of the population, which reached a peak of 5,240,800 in 1974. Thereafter it began to fall slowly, moving down to 5,062,940 in 2000. There was also a decrease in some urban populations as a result of slum clearance, overspill and relocation to new towns, with the population of Glasgow falling from over a million in 1951 to 629,000 in 2001. Rural areas also saw a loss of population, particularly the Highlands and Hebrides. In the early part of the twenty-first century Scotland saw a rise in its population to 5,313,600 (its highest ever recorded) at the 2011 census.

## See also

- Demographic history, global perspective
- Demography of Scotland

Demographic history of the United Kingdom