Key Points and Summary – South Korea’s KF-21 Boramae is moving from initial production toward a multi-block upgrade plan that aims to push the jet deeper into “5th-gen-like” territory.
-Citing defense budget materials, local and trade outlets report Block II is in planning while a conceptual Block III—sometimes dubbed KF-21EX—would add internal weapons bays, improved low-observable shaping/materials, and an indigenous engine to replace the current GE F414-GE-400K. KAI says Block I development remains on track into late 2026, with stealth-heavier features following later.
KF-21 Fighter from South Korea. Image Credit: Creative Commons.
-Separate contracts signed this summer bring the first 40 aircraft by 2028, while Seoul and Jakarta also revised Indonesia’s cost share on the program after payment delays. Officials caution the KF-21EX would not match the F-35’s stealth, but would materially reduce signature and expand mission flexibility.
South Korea Plans to Upgrade KF-21
The KAI KF-21 fighter jet, nicknamed the “Boramae,” was developed jointly by South Korea and Indonesia. South Korea reportedly was set to begin mass production of the KF-21 in the spring of 2024, with plans to procure 40 aircraft at a cost of 238.7 billion won ($178.6 million).
The KF-21 is manufactured by Korea Aerospace Industries (KAI). It is meant to fill a void left by the retirement of older aircraft such as the F-4 and F-5, the nation’s defense minister stated at the time.
According to the Korea Times, the KF-21 reached tentative combat sustainability in 2023. The goal was to reach final combat sustainability in 2026.
Now, a new report suggests that the KF-21 is already undergoing a significant upgrade.
Going 5th Gen on KF-21
According to Defence Blog, which cited defense budget documents, South Korea is planning “sweeping enhancements” to the KF-21 that would bring the jet into the class of fifth-generation stealth fighters.
Per the report, upgrades would include “internal weapons bays, advanced radar-evading materials, and a next-generation engine developed entirely in-country.”
The report stated that KAI is “currently finalizing Block I development” of the jet. Planning for Block II is underway, along with “conceptual Block III upgrades.” The stealth capability would be part of Block III.
The budget request includes 86 billion won for “development of an indigenous advanced jet engine,” and 630 billion won for “stealth-related sensor and material technologies.” Currently, the jet uses the U.S.-made GE F414-GE-400K turbofan engine.
The plan, per KAI, is still to finish Block I development by late 2026. Full stealth capability would come later.
According to a separate report by The War Zone last month, the advanced, stealthier version of the jet would be called the KF-21EX. The jet, per that report, “will not offer the same level of low observability as the F-35, which is also operated by South Korea.”
Other changes, per The War Zone, would include “a reprofiled canopy, a radome with reduced radar cross-section, an upgraded electronic warfare suite, and new conformal antennas.”
In addition, according to an Overt Defense report, KAI reached an agreement in June to build 20 more of the KF-21 jets.
KF-21. Image Credit: Creative Commons.
“The two contracts together will deliver 40 fighters by 2028 and greatly bolster the combat strength of the Republic of Korea Air Force,” the report said. “The KF-21 will have roughly 50% more range than an F-16, along with a 34% longer airframe life and advanced systems like AESA radar and secure data links.”
An Updated Agreement
South Korea and Indonesia this June signed a revised agreement on the creation of the KF-21, Breaking Defense reported, citing the South Korean Defense Acquisition Program Administration (DAPA). Indonesia agreed to revise its share of payments, after a long period of “failing to make payments in line with the original agreement it had made in 2016.”
DAPA announced that Indonesia was facing “currently initiating administrative procedures to pay the remaining share for the joint development of the KF-21.” Indonesia had committed to paying for 20 percent of
the costs, in exchange for receiving “one of the prototype aircraft and technology transfers.”
But as it fell behind, Indonesia’s contribution was reduced to 7.5 percent. There was also controversy in 2024 when engineers from Indonesia sent to study the program were accused of trying to steal technical data. A subsequent review, however, found “no major problems,” per a 2024 report.
Meanwhile, according to The Defense Post, India has denied any interest in purchasing the jets.
About the Author: Stephen Silver
Stephen Silver is an award-winning journalist, essayist, and film critic, and contributor to the Philadelphia Inquirer, the Jewish Telegraphic Agency, Broad Street Review, and Splice Today. The co-founder of the Philadelphia Film Critics Circle, Stephen lives in suburban Philadelphia with his wife and two sons. For over a decade, Stephen has authored thousands of articles that focus on politics, national security, technology, and the economy. Follow him on X (formerly Twitter) at @StephenSilver, and subscribe to his Substack newsletter.
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