Russia’s invasion of Ukraine has drawn concern and comparison to what China may have in mind for Taiwan. U.S. partners and allies can use this crisis to help them better understand — and adjust — their response to a potential future Taiwan crisis.

In Japan, the public is debating what Ukraine’s invasion could mean for Taiwan, adding momentum to discussions of “enemy base strike capability.” The attention has gotten so great that Chinese Foreign Minister Wang Yi warned Japan not to join any U.S.-led coalition against China. But given China’s history of provocations, it could behoove Japanese leaders to devote renewed attention to how they would deal with a Taiwan crisis, especially as it could include an attack on Japan. There are four items Japan should be considering.

The first is readiness of the Self-Defense Forces (SDF). Japan’s demographic decline has resulted in a smaller and older force, leaving personnel deficits in its services. Combined with consistent criticism that not all SDF exercises are geared toward realistic scenarios, policymakers could benefit from examining whether the SDF forces are at sufficient levels of combat readiness.

It is assumed that Tokyo would call up reserves, but this is not a large pool and their readiness levels are unknown. If significant combat losses were to occur, what options would Tokyo would have since a draft is unconstitutional? Policymakers should give more thought to increasing personnel staffing and creating more realistic exercises.

A second issue is the legal structure for operational responses. At the onset of any conflict, rapid political decisions are required. Because Japan’s current legal interpretations prevent any use of force until three political conditions are fulfilled, Tokyo may have to wait for a direct attack before operational actions can be taken.

For example, although Japan can legally position the SDF outside of bases in peacetime, it requires the permission of landowners. Similar limitations confront U.S. forces. Without the ability to quickly position forces outside of existing bases — even before hostilities begin — much of the initial battlespace could be ceded to China. Because these limitations are known, Japanese policymakers could benefit from considering what can be pre-approved to ensure political timelines do not hamper critical operational timelines.

A third issue is ensuring necessary capabilities and capacities. China has spent years investing in capabilities that can bring lethal force rapidly across the Taiwan Strait via major naval and airborne elements, accompanied by waves of missile strikes. Those same capabilities threaten Japan.

This suggests the need for Japan to prioritize some types of weapons over others. For example, a deep magazine of anti-air and anti-ship missiles and a large fleet of multiple-launch rocket systems would appear necessary. And because the distance from China provides Japan some operational advantages, maintaining its robust air fighter fleet and surface and sub-surface fleets is critical.

In addition to stockpiling ballistic missile interceptors, Japan could give more attention to establishing mobile integrated air and missile defense capabilities to address Chinese cruise missiles and air power. Japan could particularly benefit from focusing on capabilities available today, such as more Patriot batteries, the Terminal High Altitude Area Defense system and the more mobile U.S. Army Tactical Missile System or High Mobility Artillery Rocket System.

Sustainment capabilities also would likely be critical as any East China Sea conflict would require operations over a vast maritime domain where forward basing of key logistics capabilities could be vulnerable. Most of these are on Japan’s four main islands, not near Taiwan. This not just limits operational flexibility, but necessitates robust air and sea lift, aerial and maritime refuelers and well-stocked munition depots in different locations.

Japanese policymakers should ask themselves whether current efforts are sufficient. For example, are three Ōsumi-class ships sufficient for combat sealift needs? Are Japan’s C-130 and C-2 cargo planes capable of quickly transporting Patriot anti-air and Type-12 anti-ship missile batteries? Similarly, are the SDF’s fleet of maritime oilers and aerial refuelers adequate for concurrently supporting high-end combat in different areas? Finally, are the SDF’s concealment and deception efforts sufficient to avoid heavy damage? If the answer to any of these is negative, now is the time to consider how to address these shortfalls.

A final issue is external support. Ukraine has been able to stay in the fight not just because of the tenacity of its people, but because of external assistance. While Japan would expect any attack to be met by U.S. support, if the U.S. is also involved in a conflict, Japan could face numerous challenges.

Although Japan has domestic suppliers for munitions, it is highly dependent on foreign military sales. Because the U.S. would also be dependent on similar U.S. suppliers during a conflict, U.S. production capacity to supply Japan could be constrained. Are there bilateral prioritization agreements to ensure the requisite defense materiel without crowding out each other?

Would NATO — or select NATO members — help Japan? Without NATO membership, no NATO member is willing to directly defend Ukraine; but these countries are providing ammunition and equipment. Even if we assume other U.S. allies want to assist, geography and the lack of access to nearby bases could challenge quick and sustained support. Japan has made significant efforts to get closer strategically with key U.S. allies, but Japan should consider whether it could further enmesh itself with these states. Possible options include joint operational planning, reciprocal basing and prepositioning equipment in Japan.

The Ukraine crisis has demonstrated war can occur at any moment. Japan should ensure it is fully prepared for a potential Chinese threat.

Jeffrey W. Hornung is a senior political scientist at the RAND Corp.

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