Stunned Defense Ministry officials were scrambling to determine whether a Chinese military plane intentionally or mistakenly violated Japanese airspace off the Danjo Islands in Goto, Nagasaki Prefecture.

The incident on the morning of Aug. 26 was the first confirmed intrusion into Japanese airspace by a Chinese military aircraft.

“There is no doubt that a military aircraft violating territorial airspace sends a very strong message,” a senior official of the Self-Defense Forces said.

Territorial airspace covers areas extending about 22 kilometers from a country’s coastline. Free navigation in territorial airspace without permission is not permitted under international law.

The Japanese government has lodged a protest with China over the violation by the Y-9 intelligence-gathering plane, which prompted the SDF to scramble fighter jets.

The incident occurred at a time when China is stepping up its military activities around Japan.

Nonmilitary Chinese aircraft have twice violated Japanese airspace: a Chinese government oceanic administration aircraft in 2012 and what is believed to be a drone in 2017.

Both flew in airspace around Japan’s Senkaku Islands, which China also claims sovereignty over, in Okinawa Prefecture.

Therefore, Japanese officials were shocked that the latest airspace violation occurred in Nagasaki Prefecture, not near the Senkaku Islands in the East China Sea.

“It would be ‘understandable’ if it were the Senkaku Islands, but Nagasaki is a surprise,” a source close to Prime Minister Fumio Kishida said.

Some in the Defense Ministry and SDF suspect the Chinese Y-2 plane “simply took a wrong course and entered Japan’s territorial airspace.”

After analyzing the route of the Chinese plane, a ministry official said, “We can assume that the sharp angle the plane took immediately after the airspace violation may have been caused by panic by the pilot.”

The official said the plane was likely collecting intelligence about two Air SDF monitoring radar facilities in the area.

“The aircraft that violated Japan’s airspace this time has been gathering information on the SDF radar frequencies,” the ministry official said. “It is natural to assume that the aircraft entered the airspace while concentrating on intelligence gathering.”

The official said Japan must be vigilant about the fact that Chinese military aircraft are conducting intelligence gathering activities so close to the airspace of the Japanese mainland.

In fiscal 2023, the SDF scrambled jets 669 times, including 479 due to maneuvers by Chinese aircraft.

From April to June this year, 105 of the 159 SDF scrambles concerned Chinese aircraft.

A senior SDF official was perplexed about the latest intrusion, saying “I don't know why it happened at this time.”

Although the Chinese government has not released a statement on the airspace violation, the SDF official suggested the move was Beijing’s way of responding to an earlier incident.

In July, China’s Ministry of Foreign Affairs said a Japanese vessel had sailed through Chinese territorial waters without permission, and that Beijing had asked Tokyo to prevent a recurrence.

According to the ministry, Japan explained the incident as a “technical error.”

A source said the vessel in question was a Maritime SDF vessel.

“The Chinese side may have suspected that the Japanese side had other intentions,” a diplomatic source said.

The view that the airspace violation around the Danjo Islands was “payback” for the MSDF’s action in July has spread on social media, including among Chinese military bloggers.

China has become increasingly concerned about the Kishida administration’s efforts to deepen the U.S.-centered security framework, including the strengthening of command and control coordination between U.S. forces in Japan and the SDF.

Japan is also increasing defense spending and forming a “quasi-alliance” with the Philippines, which has had run-ins with China in the South China Sea.

Bonji Ohara, a senior fellow at the Sasakawa Peace Foundation whose expertise is Chinese military issues, said the reason for the latest airspace violation was not immediately known.

But he said, “I do not see any merit for China to militarily intimidate Japan at this time.”

Ohara noted that the Y-2 plane “clearly violated international law and took a high-risk action that could have resulted in it being shot down.”

“The aircraft may have been attempting to collect information on radio signals, SDF scrambles and U.S. military bases in Kyushu,” he said. “But it usually turns back just before the airspace. The severity of the incident depends on whether it was intentional or a mistake.”

(This article was written by Nobuhiko Tajima, Nen Satomi, correspondent Sotaro Hata, and Akihiro Nishiyama.)