Time to decide: A critical moment in Japan-US missile defense cooperation

There is no more important bilateral air and missile defense cooperative relationship than that between the United States and Japan. In the 1980s, Japan became the first non-NATO adopter of the Patriot air defense system, now used by 18 nations. Cooperation also includes Aegis ships, space sensors, PAC-3 production, SM-3 IIA for ballistic missile defense, AMRAAM air-to-air missiles and co-development of the Glide Phase Interceptor for hypersonic defense. In the coming months, Japan will develop the FY2027 budget and three new documents: the National Security Strategy, National Defense Strategy and Defense Buildup Plan (DBP). Prime Minister Takaichi Sanae has said that these documents “will determine our country’s fate.” Takaichi is likely right. These documents could incorporate decisions that will shape the character of the missile defense relationship for years to come — and not necessarily for the better. Defense Minister Shinjirō Koizumi has highlighted the centrality of countering air and missile threats to what JMOD calls the “new ways of defense.” The United States is fortunate to have its Japanese ally move with such urgency. Japan’s defense expenditures rose to $58 billion this year. Their overhaul of defense export restrictions and the 2025 sale of PAC-3 interceptors likewise represent impressive steps forward. America will need Japan’s further help to both improve air and missile defense capability and increase joint production. These cooperative efforts will continue to evolve, especially given the demand for increased production following the considerable depletion of interceptors during Operation Epic Fury. The demand for greater capacity, including SM-3 IIA, can be met partly by increased production in Japan. Other means of supplemental production will likely be necessary, either with facilities operated by Japanese industry, or by subcontracting American solid rocket motor companies as suppliers. Despite these many promising developments, there is a problem: a potential split on Patriot modernization. At the core of Japan’s missile defense modernization effort is improved sensor coverage, including the new 360-degree Lower Tier Air and Missile Defense Sensor (LTAMDS) radar, which will support the Patriot system operated by the Aerospace Self Defense Force (ASDF). If you cannot see a threat, you cannot kill it. Defeating air-launched ballistic missiles, hypersonic gliders, drones and cruise missiles requires 360-degree detection and tracking. Written in 2022, Japan’s DBP included LTAMDS acquisition as the next step to modernizing its Patriot force. Four years have now transpired, however, without any progress acquiring that radar. Threats from maneuvering aerial threats like drones and cruise missiles have since become ubiquitous. DBP modernization plans for Patriot now stand in jeopardy. The reason for Japan’s impasse has to do with a complicated set of dynamics about how radars relate to command and control (C2) systems. The US A…