South Korea picked Lockheed Martin’s F-35A stealth fighter as its main combat aircraft to better respond to possible nuclear and missile attacks from the Democratic People’s Republic of Korea (DPRK), the Joint Chiefs of Staff (JCS) said Friday.

JCS Chairman Choi Yun-hee held a meeting with top commanders of the Army, Navy and Air Force to decide on the number and requirements for jets to be bought under the next-generational fighter jet procurement program.

“The required operational capability (ROC) for next- generational fighter jets was revised to prepare for realized nuclear and missile threats from North Korea (DPRK). The kill chain system requires a jet that can infiltrate secretly into and strike a target,” Col. Eom Hyo-sik, JCS spokesman, told reporters at a briefing.

Eom said fighter jets with cutting-edge stealth functions and avionic warfare capability were needed to deter the DPRK’s future provocations through firm retribution tools.

South Korea planned to sign an agreement in 2014 to buy 40 F-35 Block 3s, further 20 jets still open, which can carry 2 air-to-ground and 2 air-to-air missiles within the body of the plane, before taking the delivery for four years from 2018.

The number of jets to be bought fell to 40 from the initial plan of 60 in order to push for the fighter procurement project rapidly and minimize security vacuum, the JCS said. The remaining 20 jets will be purchased by 2023 after reviewing changes in security situation and aviation technology development.

The F-35 fighter was selected on the back of its radar-evading capability. The detailed radar cross section (RCS) rate was not stipulated in the revised operational capability, but the lower RCS rate of the F-35 was seen as top priority in selecting Seoul’s main fighter model.

The RCS rate is the size of fighter jets shown on the radar. The lower the RCS rate, the stealthier the fighters are. The F-35 jet is known to be shown on the radar as a bird size, making it almost impossible to detect the fighter.

However, the F-35 can only carry 4 missiles and bombs as it should contain missiles within the body to improve radar-evading capability. It is picked as one of disadvantages of the fighter along with high maintenance costs.

“High-performance stealth fighters are the core of the kill chain system to infiltrate secretly and strike a target effectively with a minimum of fighters,” Brig. Shin Ik-hyun of the JCS strategy planning department told reporters.

The kill chain system refers to the Seoul-driven counterattack strategy, which preemptively detects and intercepts missiles and nuclear threats from Pyongyang. Seoul and Washington agreed in October to first strike the DPRK if signs of Pyongyang’s nuclear attacks are detected.

South Korea reportedly planned to purchase four Global Hawks from the United States with the aim of deploying the high-altitude, long-endurance unmanned aerial vehicles (UAVs) on the Korean Peninsula by 2017.

Meanwhile, the JCS meeting decided to turn the indigenous fighter jet development project, named KF-X, from a long-term plan to a mid-term project, aiming to complete the development by 2020.

The selection of the F-35 was widely expected to delay the homemade fighter project as the stealth jets should be purchased via the U.S. Foreign Military Sale (FMS) program needed to win approval from the U.S. Congress.

In the latest competitive bidding, South Korea offered the transfer of technology as one of the main requirements to be picked as a main bidder. It was part of efforts to link the procurement program to the indigenous fighter jet development project.

But, the FMS program, or the one-way government-to-government contract, would grant Seoul less room for the technology transfer in future negotiations with Washington.