Japan’s Ministry of Defense (JMOD) released the 2025 edition of its annual security report, the Defense White Paper, on July 15, 2025. In this year’s publication, the ministry revised its description of the Taiwan situation compared to last year and highlighted the expanded role of the China Coast Guard (CCG).
According to the JMOD, in past military exercises simulating a Taiwan invasion, China predominantly employed scenarios featuring the People’s Liberation Army (PLA) as the main actor. For instance, during a series of military activities conducted in August 2022 in response to U.S. House Speaker Nancy Pelosi’s visit to Taiwan, nine ballistic missiles were launched. In addition, the Joint Sword exercise in April 2023 saw a PLA naval task force—including the aircraft carrier Shandong—operate in the Pacific Ocean for the first time.
However, this year’s White Paper notes that since then, the content of China’s military exercises related to Taiwan has diversified. Notably, increasing emphasis has been placed on “blockade” scenarios targeting Taiwan. The primary operational force in such blockade simulations is the CCG.
Although the China Coast Guard is officially a maritime law enforcement agency, it was placed under the Chinese People’s Armed Police Force—a component of China’s armed forces—in 2018. As such, it is expected to take part in military operations during a contingency. Indeed, the CCG participated for the first time in a Taiwan-related military exercise during Joint Sword 2024A in May 2024.
The JMOD assesses that China may intend to employ the China Coast Guard to conduct “gray-zone warfare”—a strategy designed to create a situation that cannot be clearly defined as either peacetime or wartime. For example, if China were to pursue the unification of Taiwan, it might avoid a traditional military invasion and instead use the CCG, as a law enforcement entity, to patrol waters around Taiwan, inspect or interdict ships heading to or departing from Taiwan, thereby blockading or “quarantining” the island. This approach could prevent U.S. and allied intervention while framing the Taiwan issue as an internal matter. In fact, during Joint Sword 2024B conducted in October 2024, China rehearsed the “blockade and control of key ports and areas in Taiwan,” and CCG patrol vessels were announced to have conducted operations in waters surrounding the island.
Under international law, U.S. intervention to defend Taiwan could be justified either through the exercise of collective self-defense in response to a request for assistance from Taiwan under armed attack (even though the United States does not formally recognize Taiwan as a sovereign state, this does not mean Taiwan fails to meet the legal criteria of statehood), or through the individual self-defense of U.S. forces, including those stationed in Japan, if they came under Chinese military attack.
However, in the case of a “blockade” or “quarantine” enforced by the CCG, it remains unclear whether such actions would meet the threshold of an “armed attack” required for invoking the right of self-defense. This legal ambiguity is precisely what makes gray-zone warfare centered on the CCG so challenging.
