In the decade since Japan enacted national security legislation allowing the nation to exercise its right to collective self-defense, this year was perhaps the closest that Japan has come to involvement in warfare.

A prerequisite in the legislation for Japan to exercise that right was nearing reality earlier this year.

Gen. Yoshihide Yoshida, who retired as chief of staff of the Joint Staff in August, watched with great concern as developments unfolded in that direction.

Yoshida said his trip to the United States in late June was “like a roller-coaster ride” because of the Iran crisis.

Just as his flight departed Tokyo’s Haneda Airport, the U.S. military launched Operation Midnight Hammer, a bombing campaign targeting Iran’s nuclear facilities.

When Yoshida, then the top uniformed officer of the Self-Defense Forces, was in a meeting with the leader of the U.S. Strategic Command, Iran retaliated with a missile strike against a U.S. military facility in Qatar.

The U.S. commander repeatedly rushed out of the meeting room.

With tensions mounting amid uncertainty over how far the crisis might deepen, U.S. President Donald Trump announced a cease-fire just before Yoshida was scheduled to attend a dinner party.

“I experienced firsthand how crucial it is to halt escalation,” Yoshida said.

The U.S. airstrike on Iran was not without implications for the SDF.

For the Shigeru Ishiba administration, the worst-case scenario was an Iranian blockade of the Strait of Hormuz.

A blockade could have been designated a “survival-threatening situation,” which serves as the prerequisite for Japan exercising its right to collective self-defense.

Under the security legislation, Japan can come to the defense of a friendly country that has been attacked, even if Japan has not been directly targeted.

But to exercise that right, the attack must threaten Japan’s existence or pose a clear danger to the lives of its people.

Japan depends on the Middle East for more than 90 percent of its crude oil imports, most of which passes through the Strait of Hormuz between Iran and the Arabian Peninsula.

The government views a blockade of the Strait of Hormuz as directly impacting Japan’s national security.

In fact, during Diet deliberations on the security legislation, then-Prime Minister Shinzo Abe cited mine-clearing in the Strait of Hormuz as a specific activity the SDF could undertake in a survival-threatening situation.

Immediately after the U.S. attack on Iran, the Defense Ministry prepared to hold discussions about possible options for the SDF.

According to ministry sources, an instruction went out internally to begin “mental exercises” to consider what scenarios might arise and what options would be available.

As the Iran crisis quickly subsided, a detailed examination never materialized.

However, had Japan designated its first-ever survival-threatening situation, potential options could have included: dispatching minesweepers to the Persian Gulf for mine-clearing; sending patrol aircraft for warning and surveillance activity; and deploying destroyers to protect naval vessels of the United States and other countries, the sources said.

The potential trigger for Japan exercising its right to collective self-defense still looms as conflicts continue to plague the Middle East.

Government officials have also discussed a contingency involving Taiwan as another realistic potential trigger for a survival-threatening situation.

A U.S. intelligence agency assesses that China will possess the capability to invade Taiwan by 2027. The security community in Washington believes that in the event of a Chinese invasion of Taiwan, U.S. military bases in Japan could also be targeted by Beijing.

During a visit to the United States in January 2024, former Prime Minister Taro Aso said there is a strong possibility that Japan would determine a Taiwan contingency to be a survival-threatening situation.

Since the security legislation was enacted in 2015, the SDF has conducted tabletop exercises on the assumption that a survival-threatening situation is declared and repeatedly reviewed actions that would be legally permissible.

Given the increasingly tense international climate and the deteriorating security environment around Japan in recent years, a senior Defense Ministry official said, “What was being debated in the Diet 10 years ago is increasingly becoming a realistic concern.”

(This article was written by Daisuke Yajima and Mizuki Sato.)