South Korea possessed 63% of the necessary technology to produce the KF-X, and sought cooperation from other countries. To facilitate a technology transfer, the Agency for Defense Development (ADD) proposed two primary concepts for the KF-X: C103, which resembled the F-35; and C203, which resembled European fighters with forward canards (the design chosen would depend on whether a development deal was reached with the US or European partners). The C501 ( KFX-E) was a third design, proposed by KAI and supported by the Defense Acquisition Program Administration (DAPA), 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. ROKAF preferred the benefits of a twin-engine design, with better combat performance and safety, and a larger airframe with room for upgrades. These upgrades could lead to a future reclassification as a fifth-generation fighter, while the C501 was closer to fourth generation.