07-08-2025
South Korea's KF-21 Fighter To Get Stealthier With Internal Weapons Bays
Korea Aerospace Industries (KAI) has provided us with a look at the future, stealthier version of its KF-21 fighter, which is now known as the KF-21EX. Concept artwork of the refined version of the jet has been released, with internal weapons carriage being its distinguishing feature. This is part of an effort to make the KF-21 more survivable in the face of ever more capable air defense systems, although the resulting aircraft will not offer the same level of low observability as the F-35, which is also operated by South Korea.
The officially released computer-generated rendering from KAI shows the KF-21EX with its new, twin internal weapons bays open. The KF-21EX is shown carrying what looks like a pair of 2,000-pound-class guided bombs internally. However, there are differing reports on whether the total payload amounts to 2,000 pounds or if two such weapons can actually be accommodated.
Other visible changes to the aircraft include a sensor below the nose that performs the same kinds of functions as the Electro-Optical Targeting System (EOTS) found on the F-35, as well as on various other fifth-generation fighters. The F-35's EOTS is primarily a sensor for air-to-ground targeting, but has an infrared search and track function, as well. In this case, the new EOTS may well replace the original IRST sensor mounted ahead of the KF-21's cockpit.
Less obvious changes in the KF-21EX will include a reprofiled canopy, a radome with reduced radar cross-section, an upgraded electronic warfare suite, and new conformal antennas. KAI also says the jet will feature advanced situational awareness systems and undisclosed 'survivability technologies.'
Possible additional options under study by KAI for the KF-21EX include an artificial intelligence-enabled mission computer and expendable digital radio frequency memory (DRFM) decoys.
It's unclear to what degree the internal layout of the aircraft will have to be revised to accommodate the internal weapons bays, although a center fuselage that is deeper would seem to be a minimum requirement, and it may also be broader, too.
Whatever the degree of structural changes, internal weapons carriage of this kind will provide the KF-21EX with the ability to strike targets, including hardened ones, while maintaining low observability. As we have explained previously, the original KF-21, also known as the Block 1, was not designed with a high degree of stealthiness in mind:
'…The KF-21 takes a more measured approach to low-observable design and is intended to bridge the gap between the F-35 and the fourth-generation F-16, in terms of capabilities. At first, the KF-21's weapons will be carried externally, on six underwing and four under-fuselage hardpoints, unlike in the F-35 and most other next-generation fighters, which incorporate internal weapons carriage primarily to reduce their overall radar signature.
Ultimately, once in service, work is expected to begin on a more advanced derivative that will have an internal weapons bay, among other new low-observable features. In this way, the initial KF-21 will likely have around the same radar cross-section as the Eurofighter Typhoon, before later enhancements reduce this significantly.'
There were always plans to refine the KF-21, with the so-called Block 3 configuration expected to include a broader application of low-observable characteristics, including internal weapons carriage and a wider range of air-to-ground missions.
The more advanced derivative of the aircraft is now named KF-21EX, an apparent nod to the F-15EX Eagle II, a much-modernized version of the original F-15 for the U.S. Air Force, albeit not one that has a provision for internal weapons carriage.
According to KAI, the KF-21EX is primarily intended to penetrate advanced air defenses and then engage hardened ground targets, including reinforced bunkers. This is a particularly important requirement for the Republic of Korea Air Force (ROKAF), the wartime targets of which would very likely include deeply buried North Korean targets, including regime and command and control infrastructure, air defense nodes, and nuclear facilities. At the same time, the problem of penetrating North Korean ground-based air defenses has increased as of late, with the arrival of advanced Russian systems.
The 2,000-pound-class guided bombs that the KF-21EX will carry internally will likely be GBU-31 Joint Direct Attack Munitions (JDAM), which can be fitted with BLU-109 penetrating bomb bodies.
Other weapons that KAI plans for internal carriage include the company's Air-Launched Effects (ALE) and the U.S.-made GBU-39 Small Diameter Bomb (SDB). Air-to-air weapons are planned to include the locally made LIG Nex1 Long-Range Air-To-Air Missile (LRAAM) and the MBDA Meteor beyond-visual-range air-to-air missile. The Meteor is already provided as armament for the Block 1 KF-21, as an externally mounted weapon, including examples semi-recessed under the fuselage, as seen in the graphic below.
A KAI official told Aviation Week that internal weapons carriage for the KF-21EX is especially important since the 'loyal wingman'-type drone that is being developed to operate alongside it will not be able to carry munitions in the 2,000-pound class.
For the KF-21EX to operate alongside 'loyal wingman' drones, KAI is developing the Performance Improvement and Manned-Unmanned Teaming (MUM-T) Combat System. This will include sensor fusion and secure datalinks to allow the crewed fighter to collaborate with the drones. One option might be to include this in a two-seat version of the KF-21EX, which would have the advantage of a second crewmember who could be more dedicated to the 'drone-controller' mission. The Block 1 KF-21 is already being built in two-seat form. Collectively, these jets are also known by the name Boramae, meaning 'hawk' in Korean.
KAI has also outlined a particular mission scenario in which the KF-21EX will operate closely with 'loyal wingman' drones, specifically suppression or destruction of enemy air defenses. In this mission, the crewed fighter would serve as an escort jammer, presumably fitted with external jamming pods, while the drones act as stand-in jammers. The crewed and uncrewed aircraft will share real-time sensor tracks, providing for distributed targeting and threat analysis. Once again, a KF-21EX configured as an escort jammer would also benefit from having two crew members to handle such a demanding mission.
As for the 'loyal wingman' drone, South Korea earlier this year unveiled the stealthy Low Observable Unmanned Wingman System, or LOWUS, which is tailored to operate alongside the KF-21. There are other options for the 'loyal wingman' as well, with Seoul working on a growing fleet of low-observable drones as the country seeks to introduce new uncrewed technologies for a range of Agency for Defense Development (ADD) and Korean Air held a rollout ceremony on the 25th at the Korean Air Tech Center in Busan for the first prototype of the "Low Observable Unmanned Wingman System (LOWUS)," a core platform of the manned-unmanned teaming unmanned…
— kf21_military (@fa50_defense) February 25, 2025
As we pointed out in the past, having a stealth drone available to work alongside the KF-21 would make a lot of sense, especially since the initial Block 1 iteration of the fighters lacks high-end stealth attributes.
As TWZ wrote in the past:
'More generally, a stealth unmanned combat aerial vehicle (UCAV) carrying internal weapons would be an enormous advantage to the KF-21 Block 1 or Block 2 when penetrating heavily contested airspace. This would allow the manned fighter to remain at a safer standoff distance and use its highly capable Meteor missiles and AESA radar, and infrared search and track (IRST) to pick off aerial targets. This could be done, perhaps, by targeting data received from the UCAV's own sensors without the need to use the KF-21's onboard radar at all. This concept is increasingly attractive as it could allow manned fighters to remain largely electromagnetically silent, increasing their survivability, with the drone taking on the higher-risk role as a forward sensing platform.'
However, South Korea now appears to have recognized the shortcomings of drones of this kind, at least as they are currently projected, in terms of the kinds of armament they can carry. Therefore, adding internal weapons carriage to the KF-21 is seen as a prerequisite when it comes to having the ability to combine survivability with hard-hitting 'bunker-buster'-type weapons.
South Korea is developing the KF-21 to replace the ROKAF's now-retired F-4E Phantom II and still-active F-5E/F Tiger II fighters. Currently, it's planned for the ROKAF to introduce 40 KF-21s by 2028 and have a full fleet of 120 aircraft deployed by 2032. It's not clear, at this stage, whether the ROKAF wants to order the KF-21EX on top of these numbers, or if it would rather switch some of the previously planned buy to the more advanced model.
Aside from domestic orders, the KF-21EX could be a tempting prospect for various export customers. The possibility of offering it with a complementary 'loyal wingman' drone could make it even more attractive, provided that Seoul releases these technologies for sale to foreign customers. South Korea is an increasingly major player on the global arms market and, with its FA-50 light combat aircraft, has already won several high-profile orders.
With the KF-21, South Korea has taken a different approach to developing a new-generation fighter than some other nations. With the F-35 already in ROKAF service as a high-end stealth platform, the KF-21 has always been seen as a lower-end option when it comes to low observability. At the same time, the concept has always stressed the ability to insert incremental upgrades in terms of weapons, sensors, and now, with the KF-21, an enhanced degree of stealth. Although the aircraft will still fall short of the F-35 in this respect, it offers the advantages of domestic production, a considerable degree of control over further enhancements, and the possibility of lucrative exports.
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