The Jiaolong, China's first manned deep-sea research submersible, has reentered service after a major technical upgrade, completing dives in a recent hardware-testing mission in Chinese territorial waters, according to the Ministry of Natural Resources.

In a news release, the ministry said on Wednesday that during the mission, which took place from Feb 27 to Tuesday, the submersible set a record for its operational frequency — it conducted 14 dives within a 10-day period, including four days in which the vessel performed two dives each day.

The operations were supported by the Deep Sea 1, the country's first dedicated mother ship for submersibles, it added.

These high-frequency, high-quality dives significantly enhanced the Jiaolong's overall operational capability, laying a solid foundation for future intensive deployments, the release said.

The trials also validated the reliability of domestic components that replaced some of the submersible's imported systems. Key technical upgrades were tested at depths up to 3,000 meters, including direct-drive low-noise direct-current thrusters, an enhanced deep-sea hydraulic buoyancy control system and expanded emergency hydraulic system interfaces.

Three full-cycle tests were made on those domestic replacements, demonstrating improved energy efficiency and marking critical progress in localization of core systems, the ministry said.

The release noted that the upgraded Jiaolong will soon embark on multiple scientific expeditions, including the ministry's Global Deep-Sea Typical Habitat Program surveys in the Arctic, Indian and western Pacific oceans.

With over 80 planned dives this year, the submersible is poised to set a new annual operational record, advancing international marine research collaboration and supporting China's ocean exploration endeavors, it added.

Named after a mythical Chinese dragon, the Jiaolong entered service in 2010, making China the fifth country in the world to have deep-sea exploration technology after the United States, France, Russia and Japan. The vessel is capable of diving to depths exceeding 7,000 meters, and has explored waters in the Pacific, Indian and Atlantic oceans.

During a test dive in June 2012, the Jiaolong reached its deepest depth of nearly 7.1 kilometers in the Mariana Trench.

The Deep Sea 1 was primarily designed to accommodate the Jiaolong, but is also capable of supporting other robotic submersibles. The ship is able to sail more than 22,000 km in a single mission and operate for 60 days in any oceanic region.

Before the mother ship's commissioning in 2019, the Jiaolong was based on the Xiangyanghong 09, a survey vessel in service since 1978.