The South Korean government is in the same situation as the Canadian government: needing to purchase replacements for Cold War era combat aircraft and having a very limited budget to do so. After analyzing their specific needs, South Korea isn’t going to buy either the F-35 or the Eurofighter Typhoon:
On August 18th South Korea selected Boeing’s F-15SE Silent Eagle as the sole candidate for Phase III of its Fighter eXperimental Project (F-X) over Lockheed Martin’s F-35A and the Eurofighter Typhoon. The decision has drawn vociferous criticism from defense experts who fear the selection of F-15SE may not provide the South Korean military with the sufficient Required Operational Capabilities (ROCs) to counterbalance Japan and China’s acquisition of 5th generation stealth fighters.
In hindsight, Zachary Keck of The Diplomat believes that Republic of Korea’s (ROK) preference for the F-15SE over two other competitors was “unsurprising.” After all, Boeing won the previous two fighter competitions with its F-15-K jet. In 2002 and 2008, South Korea bought a total of 61 F-15K jets from Boeing. South Korea’s predilection for the F-15SE is understandable given its 85% platform compatibility with the existing F-15Ks.
However, the most convincing explanation seems to be the fear of “structural disarmament” of the ROK Air Force should it choose to buy yet another batch of expensive fighters to replace the aging F-4 Phantom and F-5 Tiger fighters. Simply stated, the more advanced the fighter jet, the more costly it is. The more expensive the jet, the fewer the South Korean military can purchase. The fewer stealth fighters purchased, the smaller the ROK Air Force.
Here is a mock-up of the F-15SE, courtesy of Wikipedia: