As the strategic environment of both the Indo-Pacific and Eurasia gets unstable, the logic of defense cooperation among allies is changing. The probability of a major crisis in the Taiwan Strait, North Korea’s growing nuclear-tipped missile capabilities, and Russia’s possible invasion of another European country by 2029—as pointed out by the German foreign minister—are all pointing to the same conclusion: the US and its allies are entering into an era of simultaneous, multi-theater risk. Under such circumstances, alliance credibility not only depends on political coordination, but on whether partners can jointly create actual defense capabilities.
At the current juncture, Japan and South Korea raise strategically unavoidable questions that were politically unimaginable barely 10 years ago—could the two countries move beyond intelligence sharing and joint exercises toward meaningful joint development of weapons? And if so, how could they avoid the earlier mistakes of past cooperative programs?
Why the F-2 Was Unsuccessful as a Cooperative Model—Not as an Aircraft
Typically, the F-2 fighter—jointly developed by the US and Japan—is remembered as a cautionary tale. Based on the F-16 and substantially modified to meet the needs of Japan’s maritime defense, the F-2 was notorious for its high unit cost and limited export potential, while critics in Washington perceived this as an expensive concession to Japan’s industrial protectionism. Tokyo’s critics regarded this project as a symbol of constrained autonomy under US technological control. Although both narratives contain elements of truth, neither side grasped the entirety of the program’s lessons.
The F-2’s fundamental problem was not technological failure. In fact, the program showcased notable progress in composite wing frame technology and its early operational use of active electronically scanned array (AESA) radar. Such outcomes helped Japan preserve its aerospace engineering base and later initiatives, including participation in the Global Combat Air Programme (GCAP). The genuine failure lay in the institutional design of the partnership; decision-making authority was asymmetric, Japan’s export flexibility was severely limited by US regulations, and industrial workshare was heavily influenced by political compromise rather than efficiency. As a result, an expandable cooperation model was not created.
Such experience is occasionally used as evidence that joint defense development is inherently flawed. However, in reality, it demonstrates something more specific: co-development breaks down once a partner dominates technology, market accessibility, and rule-setting. That condition does not apply in the same way to today’s Japan–South Korea partnership.
Unlike the US–Japan relationship, Japan and South Korea would initiate any potential co-development from a middle-power status. Neither side enjoys decisive technological predominance in the defense domain, while both countries are dependent on export competitiveness in order to maintain their defense industrial bases. Threat perception—which had a substantial gap—is gradually converging as North Korea’s missile and nuclear capabilities mature, while the strategic spillover effect of a Taiwan contingency is becoming clearer. Such relative symmetry does not eliminate political risk, yet it creates incentives for balanced cooperation that used to be unthinkable in the era of F-2 development.
The strategic environment further reinforces such logic. A military conflict in the Taiwan Strait would undoubtedly absorb a large portion of US intelligence assets, missile defense capabilities, and naval forces. Under such circumstances, the importance of the Korean Peninsula would not disappear; it would become more vulnerable. The North Korean leadership has already showcased its willingness to exploit moments of allied distraction, while the expansion of tactical nuclear weapons and a variety of delivery vehicles—precisely designed to compress the decision-making timeframe—reveals a broader pattern: revisionist countries are testing whether the US and its partners can preserve deterrence in multiple theaters.
Designing Cooperation for a Multi-Theater Crisis Era
In this context, Japan–South Korea defense cooperation should be understood as a measure to reduce systemic risk rather than mere reconciliation or symbolism. The key question is how to materialize it without triggering domestic political backlash or replicating the institutional failures of past programs.
The answer lies in resisting any temptation to pursue headline-grabbing platforms and instead concentrating on capability buildup that silently strengthens deterrence. For instance, if missile defense is approached primarily through interceptors or launch authority, it would become politically sensitive; but such sensitivity would substantially subside if the center of focus is on shared sensors, tracking radars, and fire-control software. Likewise, unmanned and attributable systems—especially maritime surveillance drones and autonomous anti-submarine platforms—would clearly align with the operational needs of both countries while avoiding sovereignty concerns tied to offensive strike weapons.
Naval systems are also a promising area. Both Japan and South Korea already possess advanced combat management systems (CMS) and shipbuilding capabilities. If modular architecture and export-oriented surface combat ships are co-developed, it could reinforce interoperability while creating competitive items for third markets. Space-based early-warning and resilience technologies offer similar advantages, contributing to regional stability while not altering nuclear command-and-control arrangements.
If pursued in this manner, Japan–South Korea co-development would do more than fill each country’s capability gaps. It could signal to adversaries in the region that deterrence in Northeast Asia would no longer rely on a single hub, but on a network of capable partners that could maintain military power under pressure. In addition, it could alleviate the US burden during a Taiwan contingency and complicate North Korea’s escalation calculus by strengthening regional resilience below the nuclear threshold.
Therefore, the lessons of the F-2 fighter are not about avoiding co-development. Rather, they show that co-development must be designed around balance, scalability, and strategic objectives. In a decade of overlapping crises and compressed timetables, Japan and South Korea are now facing an opportunity to move from declaratory cooperation toward practical integration. Whether they seize this opportunity will determine not only the two countries’ security, but also the stability of the entire Indo-Pacific.
[Photo by Courtney Witt, U.S. Air Force, Public domain, via Wikimedia Commons]
The views and opinions expressed in this article are those of the author.
Dr. Ju Hyung Kim currently serves as the president at the Security Management Institute, a defense think tank affiliated with the South Korean National Assembly. He has been involved in numerous defense projects and has provided consultation to several key organizations, including the Republic of Korea Joint Chiefs of Staff, the Defense Acquisition Program Administration, the Ministry of National Defense, the Korea Institute for Defense Analysis, the Agency for Defense Development, and the Korea Research Institute for Defense Technology Planning and Advancement. He holds a doctoral degree in international relations from the National Graduate Institute for Policy Studies (GRIPS) in Japan, a master’s degree in conflict management from the Johns Hopkins University School of Advanced International Studies (SAIS), and a degree in public policy from Seoul National University’s Graduate School of Public Administration (GSPA).
