The South Korean KF-21 Boramae combat aircraft could join the elite fifth-generation stealth club with a new upgrade and join fighters like the American F-35 Lightning II, the Russian Su-57, and the Chinese J-35A.
The KAI KF-21 multirole fighter jet, developed by Korea Aerospace Industries (KAI) in collaboration with Indonesia, is classified as a 4.5-generation aircraft. However, KAI has consistently maintained that it is far ahead of other 4.5th-generation jets in terms of capability and just a little short of being classified as a 5th-generation aircraft.
The KAI chief, Kang Goo-Young, a retired Republic of Korea Air Force (RoKAF) pilot, earlier said, “They say the KF-21 is a 4.5-generation fighter, but I think that’s an underestimation. Compared to the 4.5-generation French Rafale and the European Eurofighter Typhoon, its performance is superior. So, I call it a 4.9-generation fighter, which is closer to the 5th generation (a fighter with full stealth capabilities).”
Notably, even though it was designed as a 4.5-generation platform with semi-stealth and multirole capabilities to meet immediate needs and export goals, the KF-21 program’s roadmap always included the potential to evolve into a 5th-generation fighter through phased, incremental upgrades.
South Korea has now confirmed plans to upgrade the KF-21 through a phased “block” development model, culminating in Block III (also referred to as KF-21EX), which will incorporate true fifth-generation stealth capabilities.
As per reports in the local media, these upgrades are supported by South Korea’s 2026 defense budget, which allocates expanded funding for stealth enhancements, indigenous engine development, and integration with unmanned systems, along with a host of other subsystems.
The South Korean government is reportedly investing about $453 million into Block III upgrades to the aircraft.
The goal of this effort is to create a cost-effective, export-competitive fifth-generation fighter that complements the Republic of Korea Air Force’s (ROKAF) existing F-35A fleet, while positioning South Korea as a new player in the global advanced fighter market.
Last month, the Korea Aerospace Industries (KAI) released the concept artwork of the KF-21EX, prominently showing twin internal weapons bays with a pair of 2,000-pound-class guided bombs internally.
The internal weapons carriage is designed to minimize the radar section area while carrying heavy loads. Interestingly, the airframe was pre-designed with space for these bays to limit structural changes, since the South Korean Defense Acquisition Program Administration (DAPA) and KAI planned to eventually upgrade the KF-21 into a fifth-generation stealth fighter.
The internal weapons bay will enable better penetration of advanced air defenses and enhance survivability, but may not match the F-35’s all-aspect stealth.
This is mainly because, unlike the KF-21, the F-35 was designed from the ground up as a 5th-generation stealth fighter, prioritizing low observability across radar, infrared, and visual spectrums.
Nonetheless, the KF-21 upgrade seems to be an attempt to replicate some common fifth-generation features that are also found on the F-35, including a sensor beneath the nose that carries out similar roles as the F-35’s Electro-Optical Targeting System (EOTS).
The KF-21EX will also include new conformal antennas, a radome with a smaller radar cross-section, and a re-profiled canopy, among other modifications.
According to KAI, the jet would have unidentified “survivability technologies” and sophisticated situational awareness systems. The new, upgraded aircraft will have an enhanced electronic warfare suite, and the EW sensors will be moved inside the fighter to reduce detection, as per reports.
Some reports suggest that the KAI is also developing long-range air-to-air missiles that will be integrated into the Block III KF-21 stealth aircraft.
Moreover, a transition to a fully indigenous engine with potential low-observable nozzles to reduce infrared signature, supporting supercruise capability, and extending range are also on the cards. The new engine will replace the current GE F414-GE-400K that currently powers the existing iterations of the aircraft.
Additionally, the stealthy KF-21 will operate alongside loyal wingman drones in a manned-unmanned teaming (MUMT) configuration—an approach now being adopted by all advanced air forces. The modifications in this regard will include sensor fusion and secure datalinks to allow the crewed fighter to collaborate with the drones, as per The War Zone.
Since the KF-21 is also being developed in a two-seater variant, the second pilot might be tasked with operating the drones and coordinating missions in a contested environment.
The KAI has described a unique mission scenario where the KF-21EX will work closely with “loyal wingman” drones to suppress or destroy opposing air defenses. The drones would function as stand-in jammers in this mission, while the crewed fighter, which is likely equipped with external jamming pods, would act as an escort jammer. The crewed and uncrewed aircraft will exchange real-time sensor tracks to facilitate distributed targeting and threat analysis.
Once these planned upgrades are incorporated, South Korea will join an elite group of countries with its own indigenously developed fifth-generation stealth fighters. As of now, only the US, China, and Russia have operationalised aircraft of that class, whereas Turkey is fast catching pace with its fifth-generation KAAN. The South Korean KF-21EX could also potentially beat the Indian AMCA (Advanced Medium Combat Aircraft), which is unlikely to become operational before the mid-2030s.
However, it will give stiff competition to the existing fifth-generation fighters in the market, particularly to the Russian Su-57 and the American F-35. South Korea has already made a mark in arms exports and has signed multiple contracts for FA-50 light attack aircraft.
The arrival of a stealthy KF-21 would further transform the South Korean export scene and provide a cost-effective and less-restrictive alternative to the American F-35.
KF-21 Boramae
KF-21 Boramae, a 4.5+ generation multirole fighter, marked a courageous leap in the South Korean aerospace ambitions. Since developing a full 5th-gen fighter requires massive investment and technical expertise, South Korea, with limited experience in fighter development, opted for a phased approach to manage costs and risks.
The KF-21 was designed to bridge the gap between fourth- and fifth-generation fighters, offering advanced capabilities at a lower cost than platforms like the F-35. The program was launched in 2015 as a South Korea-Indonesia partnership, with Jakarta holding a 20% stake, which was later reduced to 7.5% due to Jakarta’s financial constraints.
Developed as an advanced supersonic fighter, the KF-21 is expected to replace the South Korean Air Force’s aging F-4 and F-5 jet fleet and eventually F-16 Fighting Falcons.
It is expected to become the mainstay of the Republic of Korea Air Force (RoKAF) and improve the country’s three-axis defense system, which is aimed at countering potential threats from North Korea, as previously explained by the EurAsian Times.
Currently, the KF-21 has nine to ten external hardpoints for weaponry, depending on the configuration. Though little information is available about the possible armament aboard the aircraft, it is said to be equipped with air-to-air missiles, bombs, and cutting-edge machine guns.
Earlier, the KF-21 also conducted its first live-fire test with the long-range air-to-air Meteor missile. On the same day, DAPA confirmed the successful testing of the IRIS-T short-range air-to-air missile, further showcasing firepower diversity.
Powered by two General Electric F414 engines, the KF-21 boasts a top speed of Mach 1.81, a 2,900-kilometer range, and a 7,700-kilogram payload across 10 external hardpoints. Its stealthy airframe, equipped with indigenous AESA radar, infrared search and track (IRST), and electronic warfare systems, surpasses the F-16 in range (50% greater) and airframe life (34% longer).
The aircraft conducted its maiden flight on July 19, 2022, and almost a year later, in May 2023, it was deemed “provisionally suitable for combat. South Korean Air Force Chief of Staff Gen. Lee Young-su piloted the first test flight of the KF-21 fighter jet on February 19, 2025, reaching speeds of 1,000 km/h at an altitude of 4,500 meters over the southern coast of South Korea. This milestone flight was conducted in a KF-21 prototype, accompanied by a KF-16, to assess the aircraft’s operational capabilities.
Last year, the KF-21 Boramae completed its first aerial refueling test, marking a significant advance in its development. As confirmed by DAPA, this milestone underscored the aircraft’s potential for extended-range operations.
More recently, Hanwha Systems rolled out the first mass-produced active electronically scanned array (AESA) radar for the KF-21 fighter jet, marking a significant milestone in the nation’s drive to develop advanced fighter avionics domestically. Often referred to as the “eyes” of a fighter jet, AESA radars provide simultaneous multi-mission capabilities, including tracking airborne, ground, and maritime targets.
The KF-21 Boramae has both single-seat and two-seat variants. The primary configuration is the single-seat version, designed for operational multirole missions such as air superiority and ground attack. A two-seat variant, primarily for training purposes, is also in development and has been used in testing.
The Block I variant reportedly focuses on air-to-air combat with limited air-to-ground and is expected to be deployed by 2026, whereas the Block II variant will come with enhanced software for full multirole capabilities.
According to reports, the development of Block II multirole features, including air-to-ground munitions like air-launched ballistic missiles (ALBM), has been fast-tracked by 1.5 years to early 2027. The ROKAF is prioritizing ground-attack integration to bolster overall air power.
The Block III upgrade that will transform the KF-21 into a fifth-generation stealthy aircraft will become operational in the 2030s.
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