South Korea’s homegrown KF-21 Boramae fighter has flown in formation with American military aircraft for the first time, marking a significant milestone for Seoul’s indigenous fighter programme and highlighting growing military interoperability between South Korea and the United States.
The formation flight took place over the Yellow Sea on October 23, 2026, when the KF-21 joined a group of US aircraft, including the U-2S Dragon Lady high-altitude reconnaissance aircraft, F-35 Lightning II stealth fighters and F-16 Fighting Falcons. The event, described as a “Friendship Flight,” took place three days before the beginning of the US-South Korea biannual combined air exercise, Freedom Flag, which commenced on October 26.
The KF-21, assigned to the 156th Fighter Squadron of the 16th Fighter Wing, participated alongside American aircraft in an activity designed to demonstrate the ability of the two countries’ air forces to operate together.
The Republic of Korea Air Force (RoKAF) reportedly deployed a broader formation that included its own F-35s, F-15K Slam Eagles and FA-50 light combat aircraft, in addition to the KF-21.
Notably, the KF-21 was not formally included in the Freedom Flag exercise. Instead, its participation in the formation flight was described as an observational activity intended to familiarise the new fighter with combined operations and provide experience ahead of the wider exercises.
South Korean officials said the Friendship Flight offered the KF-21 an opportunity to gain valuable operational exposure alongside US aircraft.
The US Seventh Air Force also highlighted the significance of the event, stating that the flight demonstrated the combined interoperability and combat readiness of the US and South Korean air forces on the Korean Peninsula.
“The Friendship Flight demonstrated the combined interoperability and combat readiness of the US Air Force [and Korean Air Forces] on the Korean Peninsula, showcasing how the air forces of both nations integrate directly during flying operations,” the Seventh Air Force said.
Beyond its operational significance, the formation flight carries considerable technological and strategic importance. It brings together an American fighter ecosystem and an indigenous South Korean aircraft whose development was partly accelerated by Washington’s earlier refusal to transfer several critical military technologies.
The KF-21 programme represents one of South Korea’s most ambitious defence-industrial projects, reflecting Seoul’s determination to reduce dependence on foreign suppliers while maintaining close military cooperation with the United States.
The origins of the programme date back to 2001, when then-President Kim Dae-jung proposed developing an indigenous combat aircraft to strengthen South Korea’s aerospace industry and replace its ageing fighter fleet.
However, the programme encountered a major technological obstacle in 2015.
At the time, South Korea was seeking access to several advanced technologies from the United States through an offset arrangement associated with its purchase of F-35A Lightning II fighters.
Washington declined to transfer four critical technologies that Seoul considered important for the development of the KF-21.
These reportedly included an active electronically scanned array (AESA) radar, an infrared search-and-track (IRST) system, an electro-optical targeting pod and a radio-frequency jammer.
Together, these technologies form an essential part of a modern fighter’s sensor, targeting and electronic self-protection capabilities.
The US decision was driven by export-control restrictions designed to protect sensitive military technologies rather than an attempt to undermine South Korea’s fighter programme. Nevertheless, it forced Seoul to accelerate domestic research and development.
South Korea subsequently developed the restricted systems through its own defence-industrial network.
Hanwha Systems led the development of the KF-21’s AESA radar, while South Korean companies also developed the aircraft’s infrared search-and-track system, electro-optical targeting equipment and electronic-warfare capabilities.
South Korea has maintained that it secured approximately 87 per cent of the technologies required for the aircraft, while also obtaining additional technologies from the United States.
The result is a fighter with a substantial indigenous technological foundation, although it continues to rely on foreign components, particularly its twin General Electric F414 engines.
Interestingly, Washington’s refusal to transfer the four technologies may ultimately have created an important commercial advantage for South Korea.
Because the principal mission systems were developed domestically, Seoul has greater control over their modification, modernisation and potential export to foreign customers.
Udayini Aakunoor, an aerospace and defence analyst at GlobalData, highlighted this advantage when the company published its Global Military Fixed Wing Aircraft Market 2026–2036 report.
According to Aakunoor, the US refusal to release the technologies has become one of the KF-21’s strongest selling points because South Korea can independently modify, upgrade and clear its domestically developed mission systems for foreign buyers without seeking additional approval from another government.
This could become particularly important as South Korea attempts to position the Boramae as an alternative to more expensive and technologically restricted Western fighter aircraft.
The KF-21 has also elevated South Korea into a relatively small group of countries capable of designing and producing advanced supersonic combat aircraft.
Developed by Korean Aerospace Industries (KAI), the Boramae is officially classified as a 4.5-generation multirole fighter. However, its manufacturer has repeatedly emphasised that its capabilities place it ahead of many conventional fourth-generation-plus aircraft.
KAI chief Kang Goo-young, a retired Republic of Korea Air Force pilot, previously argued that the aircraft’s classification understated its technological capabilities.
“They say the KF-21 is a 4.5-generation fighter, but I think that’s an underestimation,” Kang said.
Comparing the aircraft with France’s Rafale and Europe’s Eurofighter Typhoon, he argued that the KF-21 offered superior performance and described it as a “4.9-generation fighter,” placing it closer to fifth-generation aircraft.
Although such classifications are not universally accepted, the KF-21 incorporates several characteristics associated with modern advanced fighters, including a low-observable airframe design, AESA radar, infrared search-and-track sensors and an integrated electronic-warfare suite.
However, it does not currently possess the full-spectrum stealth capabilities associated with aircraft such as the American F-35 and F-22.
South Korea intends to address this gap through a phased development strategy based on successive aircraft blocks.
The programme is expected to culminate in Block III, also referred to as the KF-21EX, which is planned to incorporate more advanced stealth characteristics and expanded operational capabilities.
This gradual development approach would allow South Korea to introduce the aircraft into service relatively quickly while continuing to improve its combat capabilities through subsequent upgrades.
The latest formation flight with American F-35s and F-16s therefore illustrates an important aspect of Seoul’s strategy: developing an increasingly independent fighter industry without sacrificing interoperability with its principal military ally.
The KF-21 has progressed relatively quickly compared with several other advanced fighter development programmes.
KAI conducted the aircraft’s maiden flight in 2022, marking the beginning of its flight-testing phase. On March 25, 2026, the company rolled out the first production KF-21 at its manufacturing facility in Sacheon, South Korea.
President Lee Jae-myung attended the ceremony, highlighting the aircraft’s importance to the country’s ambitions to become a major global defence exporter.
The first production aircraft emerged less than five years after the maiden flight, demonstrating the pace at which South Korea has moved from prototype development towards serial manufacturing.
The aircraft’s formal delivery to the Republic of Korea Air Force took place in late September 2026, with the first flight associated with the official delivery ceremony marking another milestone in the programme.
KAI plans to initially manufacture 40 KF-21 aircraft focused primarily on air-to-air combat capabilities, with deliveries scheduled to be completed by 2028.
A subsequent production phase will involve another 80 aircraft equipped with expanded air-to-ground capabilities, including long-range missiles, with deliveries expected by 2032.
The programme is expected to provide South Korea with a modern replacement for its ageing F-4 Phantom II and F-5 Tiger II fighters, while potentially replacing older F-16 aircraft over the longer term.
The KF-21 programme originally began as a partnership between South Korea and Indonesia, with Jakarta agreeing to hold a 20 per cent stake in its development.
However, Indonesia’s financial difficulties and disagreements over its contributions subsequently resulted in a substantial reduction of its financial commitment.
Despite these complications, South Korea has continued to advance the programme, with domestic production and technological development increasingly becoming its central priorities.
The KF-21 is a twin-engine supersonic fighter available in single-seat and two-seat configurations.
Its primary operational configuration is the single-seat variant, designed for missions ranging from air superiority to ground attack. The two-seat version is primarily intended for training and other specialised operational requirements.
The aircraft has a reported maximum speed of Mach 1.81, an operational range of approximately 2,900 kilometres and a weapons payload capacity of around 7,700 kilograms distributed across ten external hardpoints.
Its combination of advanced sensors, electronic-warfare systems and improved aerodynamic performance is intended to provide a substantial advantage over older fourth-generation aircraft.
South Korean officials and programme representatives have also highlighted its longer airframe service life and greater range compared with the F-16.
The aircraft reportedly offers approximately 34 per cent greater airframe life and 50 per cent greater range than the F-16, although actual operational performance will depend on configuration and mission requirements.
Nevertheless, the KF-21’s current configuration still involves important compromises.
Unlike the F-35, which carries weapons internally to preserve its low-observable characteristics, the existing KF-21 relies on external hardpoints for much of its weapons carriage. This increases its radar signature when carrying external stores.
The planned development of more advanced variants is expected to address some of these limitations.
The KF-21 is increasingly becoming a central component of South Korea’s wider ambition to establish itself as a major international defence supplier.
President Lee Jae-myung has previously emphasised that South Korea wants to become “a contributor to world peace and development,” adding that the country intends to share not only its advanced weapons systems but also its technology and development experience with partner nations.
The aircraft could provide Seoul with an attractive export opportunity, particularly among countries seeking modern multirole fighters without the financial and political constraints associated with some Western platforms.
Its domestic mission systems could also provide South Korea with greater flexibility when negotiating technology transfers, maintenance arrangements and future upgrades.
However, establishing the KF-21 as a credible international competitor will require more than an advanced airframe and competitive manufacturing costs.
The aircraft must demonstrate operational reliability, combat effectiveness, weapons integration and long-term maintenance support. It will also need to compete against established platforms such as the F-16, Rafale, Eurofighter Typhoon and F-35.
Whether the KF-21 can emerge as a more affordable and less politically restricted alternative to the F-35 remains uncertain, particularly because the South Korean Air Force itself operates the American stealth fighter.
The aircraft’s reliance on US-made F414 engines also means that its export prospects will not be entirely free from foreign technology restrictions.
Nevertheless, South Korea’s growing control over its radar, sensors and electronic-warfare systems could provide a meaningful advantage in future negotiations with prospective customers.
The October 23 formation flight offers an early indication of how Seoul intends to integrate its new fighter into the existing regional security architecture.
The KF-21 still has years of operational testing, weapons integration and capability development ahead. Its first formation flight alongside American F-35s, F-16s and a U-2S reconnaissance aircraft does not establish combat equivalence with those platforms.
But it demonstrates that South Korea’s indigenous fighter is moving beyond the development stage and beginning to enter the operational environment alongside the aircraft of its closest military ally.
For Seoul, the strategic objective is increasingly clear: build an advanced fighter independently, retain control over its critical technologies and continue working closely with Washington.
The KF-21’s first flight in formation with American aircraft represents an important step towards achieving all three ambitions.
