[15] The KF-X advanced multirole jet fighter project, intended to produce modern warplanes to replace South Korea's aging F-4D/E Phantom II and F-5E/F Tiger II aircraft, was first announced in March 2001 by South Korean President Kim Dae-jung at a graduation ceremony of the Korea Air Force Academy.
[18] The development phase had numerous delays and postponements and its economic cost was debated, but the project received renewed interest following a 2008 feasibility study and attacks by North Korea in 2010.
[18] On 15 July 2010, a partnership was made with Indonesia, which would provide 20% of the funding for the KF-X project, cooperate with technological development through state-owned Indonesian Aerospace, and purchase 50 of the approximately 150–200 planned aircraft.
[21] In July 2022, the Polish Armaments Agency said it is closely watching the development of the KF-21 Boramae, potentially paving a way for purchase of future Block 2 version of the fighter jet.
[23][24] In May 2023, the Defense Acquisition Program Administration said that the KF-21 had passed the provisional combat suitability evaluation, to begin the initial mass production process in 2024.
[26] The initial goal for the program was to develop a single-seat twin-engine multirole fighter with stealth capabilities exceeding both the Dassault Rafale and Eurofighter Typhoon but less than those of the Lockheed Martin F-35 Lightning II.
KFX-E) was a third design,[18] proposed by KAI[30] and supported by the Defense Acquisition Program Administration (DAPA),[31] which attempted to reduce costs with a smaller, single-engine fighter, but it had inferior performance to the F-16 and was unsuitable for the large airspace of Indonesia.
[33] In May 2016, the U.S. government and Lockheed Martin tentatively agreed to transfer 21 technologies to KAI under the terms of offset trade, which is part of a contract for South Korea to introduce the F-35A.
[61] The second prototype took off from Sacheon Air Base in South Gyeongsang Province on November 10, tested its flight performance for 35 minutes, and landed safely.
The KF-21 first prototype took off from the ROKAF's 3rd Training Wing and broke the sound barrier (Mach 1.0, approximately 1,224 km/h) for the first time while flying at an altitude of about 40,000 feet over the South Sea.
[69] On May 16, 2023, DAPA announced that the fifth prototype successfully completed its maiden flight, taking off from the 3rd Training Wing in Sacheon and flying over the South Sea.
[73] On October 20, 2023, at the Seoul ADEX, the KF-21 showcased its technological capabilities during a five-minute demonstration, performing maneuvers such as horizontal sharp turns and inverted flights.
[75] DAPA announced that on the morning of the March 19th, 2024, the fifth prototype (single-seat) successfully completed an aerial refueling flight over the South Sea after taking off from the Air Force's 3rd Training Wing in Sacheon.
[21][better source needed] In July 2010, the Indonesian government agreed to fund 20% of the KF-X project cost in return for prototype 005 (designated IF-X), system development participation, technical data, and production sharing.
[91] Yonhap reported in October 2019 that, according to DAPA Korea, there were 114 Indonesian engineers participating during the peak of the KF-21 design phase in July 2019 and the development was ready to go to the prototyping stage after it met all of the requirements in September 2019.
[102] The rumors about the United Arab Emirates joining the KF-21 program was denied by DAPA Korea based on Korean government-owned media, Yonhap.
[93] Indonesian Defense Ministry Technology Director Air Vice Marshal Dedy Laksmono confirmed to the press on 29 October 2023 that the budget for 2024 cost share payment had been set aside at 1.25 trillion rupiah (US$80 million).
[106] According to a South Korean government official, in May 2023, during a visit to Korea in mid-April 2023, Sebastian Chwałek, chairman of the PGZ, expressed Poland's desire to participate in the KF-21 project.
The South Korean Defense Acquisition Program Administration said it will begin a full-fledged review once it receives a letter of intent from the Polish government.
For certain sensitive technologies, such as AESA radar, EO TGP, IRST and RF jammer, foreign companies were only consulted for testing support and technical advice in order to avoid arms-trading restrictions.
[110][133] Cobham received contracts to provide missile ejection launchers, communications antennae, external fuel tanks, and oxygen systems.
Foreign partners were sought to share costs and guarantee purchases, and several failed attempts were made to entice Sweden, Turkey, and the United States to join the project.
[150][151] In February 2017, Indonesian Vice Minister of Foreign Affairs Abdurrahman Mohammad Fachir said that the KF-X project was further delayed because the US government had refused export licenses for four key F-35 technologies.
This disapproval was reaffirmed in October 2015 talks, though the US military stated that there was an agreement to form an interagency working group on such issues and that the US Secretary of Defense would "think of ways for joint cooperation" with technology for KF-X.
[157][158][159] In November 2017, state-owned Indonesia Aerospace was overdue in its funding payment, which National Assembly Defense Committee member Kim Jong-Dae said would further delay, or suspend the project.
Indonesian state media announced that the defense ministry would renegotiate the joint development program in an attempt to gain a larger share of local production, as well as export rights.
According to the agenda of a January 2019 meeting, Indonesia sought to extend its involvement in the program to 2031, and was interested in making part of its payments in trade for Indonesian-produced defense equipment.
On 2 February 2024, the South Korean National Intelligence Service (NIS) and the Defense Counterintelligence Command (DCC) announced a joint investigation into whether Indonesian engineers dispatched to KAI violated the Defense Technology Security Act for allegedly attempting to steal classified KF-21 technical data after storing it on an unauthorized USB drive.
In May 2022, the Ministry of National Defense (MND) decided to drop funding for the CVX, a planned small aircraft carrier capable of operating STOVL F-35B jets.
If the Republic of Korea Navy (ROKN) decides to procure an aircraft carrier large enough to operate fighters and identifies a requirement, KAI claims it would be able to build the KF-21N "in a few years.