Japan has told China that a Maritime Self-Defense Force destroyer that sailed into Chinese territorial waters in July despite repeated warnings by Chinese vessels did so inadvertently, diplomatic sources said Sunday, adding that the captain has been replaced for what was viewed as a serious error.

Observers say the incident, which occurred as the destroyer Suzutsuki was monitoring Chinese military drills on the high seas, calls into question the skill levels of MSDF personnel. Tokyo is also considering disciplinary measures against other crew members, the sources said.

Japan has unofficially informed China about its findings as well as the captain’s dismissal. The incident triggered a protest from Beijing.

In the early morning of July 4, the Suzutsuki sailed for some 20 minutes in Chinese waters within 12 nautical miles (22 kilometers) of the coast of Zhejiang Province.

Photo taken from a Kyodo News helicopter shows the Suzutsuki (2nd from L), a Maritime Self-Defense Force destroyer, docked at a base in Sasebo, Nagasaki Prefecture, on Sept. 9, 2024. (Kyodo)

When an MSDF base made an inquiry after noticing the destroyer’s entry into Chinese waters, the male officer with the rank of commander, serving as the Suzutsuki’s captain, responded that he was “not aware” the ship had sailed into an “off-limits area,” according to the sources.

The officer had assumed command of the ship in May this year. An investigation conducted following the incident also revealed that there were flaws in relaying information from other crew members on duty when the destroyer entered Chinese waters, the sources said.

The officer was dismissed as captain of the ship later in July for negligence. The MSDF is also considering admonishing several other crew members for failing to fully check nautical instruments, maintain a lookout and report to the captain, the sources said.

It marked the first time an MSDF vessel had entered Chinese waters without advance notification since the establishment of the Self-Defense Forces in 1954.

The Japanese government compiled a report on the incident with the National Security Secretariat playing a key role, but it does not plan to release the document given that it concerns SDF operations.

A day before the MSDF destroyer entered Chinese waters, Zhejiang authorities said a no-sail zone would be set up in a nearby area for the Chinese military to conduct a live-fire drill. The Suzutsuki was on a mission to monitor the exercise.

Tokyo maintains the Suzutsuki’s entry into Chinese territorial waters was lawful, invoking the right to innocent passage under the U.N. Convention on the Law of the Sea.

But Beijing argues the MSDF ship failed to meet the requirements under its domestic law, which mandates that foreign vessels seek prior permission to enter Chinese territorial waters.

China criticized the Suzutsuki’s entry into its waters as an “illegal and improper move” and called for a thorough investigation and steps to prevent similar incidents.

Yoji Koda, former commander in chief of the Self-Defense Fleet, the main force of the MSDF, attributed the low skill levels among MSDF officers in the incident to a lack of training amid increased missions to guard against Chinese military activities in the East China Sea.

China regularly sends its military and coast guard vessels into Japanese territorial waters near the Tokyo-controlled Senkaku Islands in the East China Sea, which Beijing claims and calls Diaoyu.

“If MSDF officers have to spend an enormous amount of time on surveillance activities, they cannot fully acquire basic skills” required for operating the force’s vessels, Koda said, urging the Japanese government to increase personnel and equipment to rectify the situation.

In addition to the East China Sea, Chinese survey ships have repeatedly entered Japanese waters off Kagoshima Prefecture since November 2021.

MSDF vessels are also deployed in the Sea of Japan to keep watch for North Korean ballistic missile launches.

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