Japan Weighs Self-Defense Forces Deployment to Iran Ahead of US-Japan Summit

Japan faces significant constitutional and legal barriers in considering deployment of its Self-Defense Forces (SDF) to the Strait of Hormuz amid President Trump's demands for military assistance.

“The project, announced last May, aims to equip the United States with integrated defense against multiple ballistic missile systems”

Agenzia Nova

Japan's post-war pacifist Constitution, particularly Article 9, strictly limits the use of force to self-defense purposes, creating a fundamental constraint on overseas military operations.

AL-Monitor

The 2015 reinterpretation allowing 'collective self-defense' can only be invoked if Japan's survival is threatened and no other options exist, conditions that the current Iran conflict does not meet according to government assessments.

Defense Minister Shinjiro Koizumi has stated that police authority does not extend to states or state-like organizations, making maritime security operations legally problematic when dealing with Iran.

These legal limitations come as Japan's government examines whether an SDF deployment is possible within constitutional bounds, with prevailing views suggesting that as long as fighting continues, dispatch based on recognizing a survival-threatening situation will be difficult.

President Trump's demands for military assistance in the Strait of Hormuz have created a high-stakes diplomatic dilemma for Prime Minister Sanae Takaichi ahead of their crucial summit.

Trump has specifically called on Japan and other countries to dispatch naval vessels to help reopen the strategically important waterway, which has been effectively shut by Iran in response to US-Israeli attacks.

AL-Monitor

The pressure is particularly acute given Japan's heavy reliance on Middle Eastern oil—over 90% of its oil imports pass through the Strait of Hormuz—making energy security a critical national concern.

Trump has suggested that Japan owes the United States for years of defense aid and must act because of this energy dependence, creating a sense of obligation intertwined with strategic necessity.

The timing could scarcely be worse, with Takaichi meeting Trump at just the moment when his anger at the 'ingratitude' of allies is at his peak, especially after European allies have spurned similar requests.

Domestically, Prime Minister Takaichi confronts overwhelming public opposition and significant political risks in considering any military involvement in the Iran conflict.

“security alliance," said Kazuhiro Maeshima, a politics professor at Sophia University in Tokyo”

AL-Monitor

A recent Asahi poll conducted on March 14 and 15 found that 82 percent of Japanese voters oppose the US war on Iran, while only 9 percent endorse the US-Israeli attack on Iran according to another poll.

This strong anti-war sentiment creates a formidable constraint for Takaichi, who must balance diplomatic obligations with democratic accountability.

Takaichi, who led the ruling Liberal Democratic Party to victory in February in its largest electoral win since World War II, enjoys strong public support for her economic policies but risks undermining that foundation by taking unpopular military positions.

The situation has become more complicated following Trump's decision to specifically demand that China dispatch vessels to the Strait of Hormuz, with Japanese officials warning that if China responds, Japan will find itself in an even more difficult position.

Beyond the military deployment dilemma, the US-Japan summit carries significant economic and investment implications that reflect the broader strategic relationship between the two allies.

Japan has committed to investing a grand total of $550 billion into the United States under a trade deal agreed in July 2025, in exchange for Trump lowering tariffs on Japanese exports.

AsiaOne

Public broadcaster NHK reported that both sides are in the final stages of preparing to announce a joint document outlining a second round of potential investments totaling 11 trillion yen ($69.2 billion), following the first $36 billion announced in February.

These investments are expected to include next-generation nuclear reactors and natural gas power plants.

However, the original tariff reduction agreement has been complicated by a Supreme Court ruling that struck down Trump's tariff plans, with the president instead imposing 10% global tariffs.

The economic stakes are particularly high as the Iran conflict has sent crude oil prices soaring, beginning to cast a shadow over the Japanese economy and potentially undermining Takaichi's economic policy achievements.

Japan's consideration of military options is further complicated by international law concerns and historical precedents that shape Tokyo's approach to overseas deployments.

“With limited military options, Tokyo could offer to be a go-between with Tehran, said Tsuneo Watanabe, senior fellow at Japanese think tank The Sasakawa Peace Foundation”

AsiaOne

Japanese legal experts are divided over whether the US military action against Iran complies with international law, with uncertainty potentially limiting how far Tokyo is willing to go in supporting the campaign.

CNBC

The government has maintained that it does not yet have detailed information and is avoiding a legal assessment of the attack on Iran, though former Prime Minister Shinzo Abe's 2015 statement that 'rear-area support for a state that carried out a preemptive strike is out of the question' could become a significant obstacle.

Past Japanese operations in the Middle East offer a guide to Tokyo's legal limits: during the 1991 Gulf War, Japan contributed money rather than personnel; after 9/11, Japan sent MSDF vessels to the Indian Ocean to refuel US operations but avoided combat; in 2004, Japan sent ground troops to Iraq for reconstruction work with strict force limitations; and in 2019, Japan diverted destroyers from anti-piracy operations to gather intelligence but stayed outside the Strait of Hormuz.

These precedents demonstrate Japan's consistent pattern of maintaining legal compliance while providing limited support.

The summit's broader regional implications are amplified by the postponement of Trump's planned visit to Beijing and the complex US-China dynamics that frame Japan's strategic positioning.

Japan had positioned the upcoming summit as an opportunity to confirm strengthening Japan-U.S. cooperation with an eye toward the U.S.-China summit originally scheduled for April, but Trump's decision to delay his Beijing trip due to the Iran war has complicated calculations.

Tokyo is targeting a deal with Washington that would enable it to diversify supplies of critical minerals away from China and join Trump's 'Golden Dome' missile defense system against new hypersonic weapons being developed by China and Russia.

However, Takaichi's own diplomatic tensions with Beijing—stemming from her remarks in 2025 suggesting Japan could become involved militarily if China attacks Taiwan—have already soured bilateral relations.

The Japanese government has maintained contact with Iranian officials throughout the current conflict, with Foreign Minister Toshimitsu Motegi speaking to his Iranian counterpart on March 17, highlighting Tokyo's desire to preserve diplomatic options even as it faces intense pressure from Washington.