In the Indo-Pacific region, the alliance the United States has with Japan is arguably its most important. If a high-end contingency erupts in the East China Sea and the United States becomes engaged in major conventional combat operations with China, what roles can and might Japan play? In this report, Jeffrey W. Hornung assesses the strengths and limitations of Japans Self-Defense Forces (SDF), as well as legal issues pertaining to the SDF use of force and U.S. base access in a contingency for combat operations that may not be directly tied to the defense of Japan. Hornung finds that, despite Japans focus on self-defense, there are significant areas in which the SDF can assist the United States. He identifies strengths and weakness of the capabilities of each of the three SDF services-both current and expected over the next decade-and steps that could be taken to enhance these capabilities. Hornung also examines bilateral agreements and Japanese laws that govern how SDF capabilities may be employed and whether U.

S. forces can expect to access their bases in Japan for combat operations. Hornung makes specific recommendations on how to ensure more effective and capable Japanese support in an East China Sea contingency involving China, including how Japan could better position itself to respond, both for its own defense and in support of the United States, and how the United States could better support Japan in these efforts.