MELBOURNE, Australia — Taiwan has said a Chinese military plane crashed into the South China Sea in early March, with Beijing appearing to hide its rescue and recovery effort under the guise of a snap military drill.

This claim echoes that of Vietnamese open-source investigator Duan Dang, who said his sources told him a Shaanxi Y-8 maritime patrol aircraft of the People’s Liberation Army crashed into waters south of the Hainan Island on March 1.

Shortly after, China launched what is believed to be an initial search-and-rescue effort that took place between the evening of the reported crash until noon local time on March 2.

China’s Hainan Maritime Safety Administration subsequently announced a military exercise at an area south of that initial effort, with its closest point 52 miles south of the Hainanese city of Sanya. But the drill also occurred in parts of Vietnam’s exclusive economic zone east of the country’s cities of Dong Hoi and Dong Ha.

The exercise started on the evening of March 4 and is scheduled to end on the evening of March 15.

However, Dang noted that automatic identification system data from ships broadcasting via transponders in that area, plus satellite imagery, appeared to reveal ships belonging to China’s People’s Liberation Army Navy and its Coast Guard.

The fleet apparently included the Tansuo-1 and Tansuo-2, a pair of seabed research vessels capable of operating deep-sea submersibles. These ships were traveling slowly, which suggests a search of the seabed and/or the water’s surface was ongoing — instead of military maneuvers.

The director general of Taiwan’s National Security Bureau, Chen Ming-tong, confirmed the crash of a Chinese aircraft, telling lawmakers China has declared the area off limits during ongoing operations. However, the official declined to provide further details, noting that might compromise his agency’s intelligence sources.

For its part, Vietnam has criticized the Chinese military exercises, with its Ministry of Foreign Affairs calling on China to “respect and avoid violating Vietnams EEZ and continental shelf” and not to take any action that may complicate the situation.

China and Vietnam are among six countries with overlapping claims to the whole or parts of the South China Sea. The island of Taiwan is part of such claims, with the government there maintaining its independence despite China insisting it owns the territory.

It is unclear what type of maritime patrol aircraft was involved in the reported crash. The PLAN has a regiment of Y-8Q (also known as KQ-200) anti-submarine/maritime patrol aircraft based out of Hainan.

Older maritime versions of the Y-8 were seen at the PLAN’s Hainan air bases, although these have mostly been replaced by the newer Y-8Q. The Y-8Q has been the type most regularly detected by Taiwan’s Defense Ministry crossing into the island nation’s air defense identification zone, although the ministry has not noted any of the aircraft in the zone since March 1.

Su Tzu-yun, an associate research fellow with Taiwan’s Institute for National Defense and Security Research think tank, told Newsweek that this was possibly due to the Y-8Q fleet being grounded for inspection, a typical aviation protocol following a crash.

Mike Yeo is the Asia correspondent for Defense News.

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