Experts at the Center for Strategic and International Studies (CSIS) China Power Project and other think tanks predict a higher likelihood of a Chinese invasion or blockade of Taiwan after this year’s presidential elections, and as the 2027 centenary of the People’s Liberation Army (PLA) approaches.

Japanese authorities believe, though officially maintaining strategic ambiguity, the United States is likely to intervene if Taiwan’s main island is attacked. Admiral (ret.) Tomohisa Takei, in a paper published in May 2024, noted Japan's confidence in US military support, but expressed doubts about the consistency of support from other US allies.

Former Prime Minister Shinzo Abe argued that a Chinese invasion would likely breach Japanese air and sea space, effectively constituting an attack on Japan. This aligns with Japan’s 2022 National Security Strategy, which underscores Taiwan's importance as a democratic ally and “indispensable element for the security and prosperity of the international community.”

The strategy also highlights concerns over China’s military activities in Taiwan’s vicinity, including ballistic missile launches into waters near Japan. A PRC invasion or blockade of Taiwan would severely restrict Japan’s access to the open sea, particularly through the Taiwan Strait, compromising freedom of navigation and effectively isolating Japan.

As a result, many within Japan’s government and military view preparing for a possible conflict over Taiwan as essential to safeguarding Japanese national security and maintaining its strategic interests in the region.

Tokyo’s Taiwan policy is rooted in the 1972 Japan-China Joint Communiqué, which, like the US Taiwan Relations Act, recognises Taiwan as part of the People’s Republic of China (PRC) while emphasising that unification must be carried out peacefully.

Admiral (ret.) Tomohisa Takei interprets Tokyo’s stance as maintaining strategic flexibility, allowing Japan to choose whether or not to intervene in a PRC invasion scenario. Takei notes that a change in US policy, such as former President Trump stating he was open to the idea of direct military intervention and President Biden’s repeated statements that the US would fight for Taiwan (despite the White House immediately walking these statements back), could influence Japan’s response.

According to the Guidelines for US-Japan Defense Cooperation, Washington is encouraged to consult with Tokyo before using Japanese bases for military action. In such a conflict, Japan would likely provide logistical support, effectively involving it in the hostilities, and if Tokyo deemed PRC actions against Taiwan a direct threat, the Japan Self-Defense Forces (JSDF) would be expected to intervene alongside US forces.

In 2022, the Japanese government released three strategic documents: the National Security Strategy (NSS), the National Defense Strategy (NDS), and Defense Buildup Program.

Together, these documents aim to significantly enhance the capabilities of the Japan Self-Defense Forces (JSDF) to address emerging regional threats, particularly from China and North Korea.

The Defence Buildup Program justifies military expansion as necessary to counter potential “unilateral changes to the status quo by force.” While Taiwan is not explicitly mentioned, “status quo” implies few other plausible interpretations.

The documents focus on seven critical areas: establishing stand-off strike capabilities, strengthening integrated air and missile defences, deploying unmanned assets, improving cross-domain operations, advancing command and control systems, enhancing force mobility and civil defence, and increasing overall sustainability and resilience.

Key objectives include acquiring long-range missiles for counter-strike capabilities, expanding missile defence to handle advanced threats like hypersonic weapons, and investing in cyber and space defence to support multi-domain operations.

The program also seeks to double Japan’s defence spending to 2% of GDP over five years, marking a significant shift for a country traditionally focused on minimal defence posturing.

CSIS interprets Japan’s 2022 defence documents as confirming Tokyo’s “intention to make a full-fledged contribution to the defence of Taiwan” and a commitment to involve the Self-Defense Forces (SDF) in Taiwan’s defence alongside the United States.

The US Naval Institute, however, reports that while Japan’s Self-Defense Forces have significantly enhanced their capabilities over the past 20 years, this was largely driven by the direct threat posed by the PRC, especially around the Senkaku Islands.

The Institute also notes that the Treaty of Mutual Cooperation and Security between Japan and the United States of America is not a mutual defence pact: it obligates the US to defend Japan but does not require Japan to defend the US or to participate in US conflicts.

Japan’s Ministry of Defense has proposed a $59.76bn budget for fiscal year 2025, reflecting a 7.5% increase to support significant military expansion.

The primary focus is on enhancing counter-strike capabilities, including the acquisition of long-range missiles like Tomahawks and extending the range of the Type-12 anti-ship missile.

The Defence Buildup Program also prioritises integrated air and missile defence, autonomous systems, and cross-domain operational capabilities across cyber, space, and traditional domains.

Further investments are directed towards enhancing command and control systems, mobile deployment, and overall resilience and sustainability.

While these defence enhancements address threats from China and North Korea, Japan has not explicitly committed to Taiwan's defence.

However, given Japan’s reliance on the US for security and the likely risk to its own territory in a Taiwan conflict, Japan may ultimately find itself involved in a US-China war scenario, especially if a blockade or Chinese counterstrikes threaten Japanese security.

Until Tokyo formally revises its stance, however, strategic ambiguity regarding Taiwan’s defence remains the policy.