한국항공우주산업
Lockheed Martin with Korea Aerospace Industries (KAI) proposed their KAI T-50 Golden Eagle, which first flew in 2002, for the T-X program. While the T-50 was explicitly designed and built for the South Korean trainer requirement, Lockheed Martin officials acknowledged that the aircraft was designed with replacing the T-38 in mind. Hence, the Defense Department reserved the T-50A designation for the KAI T-50 in hopes of not creating confusion between two "T-50" trainers by allocating T-50 to an unrelated trainer aircraft. Lockheed anticipated proposing the T-50 with few changes, mostly avionics related. Plans were in place to build a new assembly line in the United States for manufacturing the T-50 for the United States Air Force instead of manufacturing them in South Korea, should the Lockheed Martin/KAI team win the contract.