2 new stealth fighter jets will expand who's in the world's top air forces

Business Insider

03-05-2025

Ever since the introduction of the F-22 Raptor in 2005, 5th-generation fighters have been the undisputed kings of the skies.
These state-of-the-art fighter jets have characteristics like high maneuverability, advanced electronics, the ability to supercruise, and, most importantly, low observability to enemy radar detection. They are both feared and vaunted, and are at the top of the wish lists of the world's best air forces.
To date, twelve countries operate one of the four models that can claim 5th-gen status; the American F-22 and F-35 built by Lockheed Martin, China's J-20, and Russia's Su-57. That club could grow to twenty by 2030.
But it's not just the number of 5th-gen fighter operators that's set to grow. The even more exclusive club of 5th-gen fighter producers may get two new members by the 2030s: South Korea and Turkey.
While not traditionally global military powers, both countries are increasingly seen as rising powerhouses in the global defense industry and have been hard at work for over a decade on their own advanced fighter designs.
South Korea's 'fighting hawk'
Developed by Korean Aerospace Industries (KAI) and officially unveiled on April 9, 2021, the KF-21 is South Korea's first domestically-made fighter jet, which officials aim to upgrade to a stealth fighter.
Also called the Boramae or 'fighting hawk' in Korean, the KF-21's origins stem as far back as 2001, when then-South Korean president Kim Dae-Jung declared his country's intent to replace South Korea's aging F-4 Phantom fighter-bombers and F-5 light fighters with a domestically made fighter.
The first prototype was rolled out and unveiled at KAI headquarters in 2021. On July 19, 2022, it made its maiden flight, and on January 17, 2023, it reached supersonic speeds for the first time.
The KF-21 program has since conducted over 1,000 sorties across six prototypes, including weapons separation tests and an air-to-air refueling exercise. Two of the prototypes feature a tandem seat arrangement.
The KF-21's specifications are just as impressive as its development speed. The jet can reach a speed of Mach 1.8 (or 1,400 miles per hour), has a ceiling of 50,000 feet, and can carry 17,000 pounds of ordnance.
The KF-21 also has an advanced suite of avionics and other electronics, like an active electronically scanned array (AESA) radar; a cutting-edge system that uses thousands of tiny antennas to rapidly scan, track, and target multiple objects simultaneously. The two-seater variant is expected to be capable of teaming with South Korea's Low Observable Unmanned Wingman System (LOWUS), a collaborative combat aircraft under development.
Despite its impressive capabilities, the KF-21 is not a 5th-gen fighter, as it does not have the same stealth capabilities as its American, Chinese, and Russian counterparts.
While the jet does feature an angular design to reduce its radar cross section, it lacks radar-absorbent materials (RAM) across its entire body and does not have internal weapons bays, instead relying on ten external hardpoints.
Consequently, KAI and analysts often refer to the KF-21 as a "4.5 generation" fighter — in other words, an advanced 4th-gen fighter with some 5th-gen characteristics.
But that may not be the case for long. KAI has announced that it intends to upgrade a version of the KF-21 to a full stealth fighter. Dubbed the KF-21EX, these upgrades will include internal weapons bays, more advanced RAM coatings, conformal antennas (flat sensors embedded in the airframe's skin that replace protruding antennas), and possibly low-observable exhaust nozzles for engine exhaust and infrared signature reduction. Internal weapons bays are important for a 5th-generation fighter because external weapons produce sizable radar returns.
The KF-21EX may arrive by the late 2030s or early 2040s.
South Korea's air force signed its first contract for 20 KF-21s last year, with deliveries expected between the end of 2026 and summer of 2027. A second order of 20 more is expected to come by the end of this year. The country hopes to acquire 120 of the jets by 2032.
Turkey's 'king of kings'
Turkey's entrant to the 5th-gen fighter club, the TAI TF Kaan, is claimed to be a fully fledged stealth fighter.
Turkey had planned to replace its fleet of F-16s with a mix of high-end/low-end 5th-gen fighters since 2010, with the Kaan intended to form the low-end portion and around 100 F-35s bought from the US forming the high end.
But Turkey's expulsion from the F-35 program in 2019 over its purchase of Russian air defense systems forced the Turks to commit to developing the Kaan as a fully fledged 5th-gen fighter.
In the summer of 2019, state-run Turkish Aerospace Industries (TAI) displayed a full-scale mockup at the Paris Air Show. Construction on the first parts finished in 2021, and in 2023, the jet was finally unveiled to the public and officially named the Kaan — Turkish for 'ruler.'
A little more than a year later, the Kaan conducted its maiden flight, which was followed in 2024 by a second test flight.
With a wingspan of 44 feet and a length of 66 feet, the Kaan is similar in size and appearance to the F-22. TAI officials have said that the Kaan can carry up to 20,000 pounds of ordnance, though it has been reported that it can only carry 1,000 pounds internally; Internal capacity is important for a 5th-generation fighter because external weapons produce sizable radar returns. It is also equipped with an AESA radar.
That Turkey has the capability to build a 5th-gen fighter is not far-fetched. Formerly a Tier 3 partner of the F-35 program, Turkish companies provided some 900 components for the F-35, including the air inlet ducts, exterior panels for the airframe, weapons bay doors, and other structural components and assemblies.
In fact, TAI was one of only two suppliers for the F-35's center fuselage — a critical structural core that connects the wings to the airframe and partially houses the jet's fuel tanks, weapon bays, and a portion of its avionics.
The degree of the Kaan's stealth, however, is unknown, especially since it has several features that make it difficult to maintain low observability. The Kaan's two F110-GE-129 engines (the same General Electric jet engines on F-15s and F-16s), for instance, were never designed for stealth aircraft and lack features like specially designed exhaust systems and nozzles, which would reduce both high infrared signatures and radar reflections.
More importantly, it is unknown if Turkey has radar-absorbent materials for the Kaan. The Scientific and Technological Research Council of Turkey has said that it is developing "Radar Absorbing Multilayered Thin Film Surface Coating" for the Kaan, and TAI and Turkish officials have said that the Kaan has advanced technologies that make it stealthy, but there have been no official statements on the status of the RAM's development or its quality, beyond general claims of stealth.
Two more Kaan prototypes are under construction, with three more to be built before serial production begins. TAI expects to deliver the first of 20 Kaans to the Turkish Air Force by 2028 or 2029.
More producers, more customers
The KF-21 and Kaan will almost certainly be flown by countries that previously had no real hope of obtaining stealth fighters.
Fifth-generation fighters are hard to acquire due to their cost-prohibitive prices (often in the tens to hundreds of millions of dollars per unit) and complex procurement processes. Their advanced tech make countries hesitant to share them, fearing secrets could reach hostile powers, with sales typically limited to very close allies capable of fulfilling stringent assurances.
Cheaper fifth-generation fighters from producers with fewer geopolitical constraints and ambitions to expand influence through high-end arms sales could make acquisition more feasible.
As a development partner in the KF-21 program, Indonesia is slated to acquire 48 of the 4.5-gen KF-21 variant, though issues with funding and data theft may change that. Other countries have reportedly either expressed interest or been courted by KAI, including Saudi Arabia, Malaysia, the Philippines, the UAE, Poland, and Peru — though these countries would likely opt for the 4.5-gen variant.
The Kaan, meanwhile, has received a lot of interest. Close Turkish ally Azerbaijan became a partner of the Kaan program in 2023, which might make it the first foreign customer. In January, it was reported that Turkey and Pakistan may establish a joint factory for Kaan production, and that Saudi Arabia had expressed interest in acquiring 100 of the fighters. The UAE has also reportedly indicated interest in joining the program as well.
Ukraine, meanwhile, has expressed interest in both purchasing the Kaan and competing for a future contract that would see it be involved in the production of its future engines.
Even if the initial versions of the KF-21 and the Kaan do not prove to be as stealthy as their American, Chinese, or Russian counterparts, their development so far shows that the monopoly held by the world's superpowers on 5th-gen aircraft is likely approaching its end.
Moreover, it may also serve as something of a warning that more countries — including ones not seen as global or even regional powers — may field their own undetectable aircraft in the near future.
Benjamin Brimelow is a freelance journalist covering international military and defense issues. He holds a master's degree in Global Affairs with a concentration in international security from the Fletcher School of Law and Diplomacy. His work has appeared in Business Insider and the Modern War Institute at West Point.