QINGDAO - The record-breaking crew of China's Jiaolong manned submersible were on Monday welcomed back to land with a letter from Vice Premier Li Keqiang, who hailed their achievements as a huge boost for the country's efforts to protect and develop maritime resources.

"The research and development of the Jiaolong manned submersible and its successful diving operations marked a huge step forward for our country's deep sea equipment and technology," according to Li, whose remarks were read aloud by Xu Shaoshi, minister of land and resources, at a ceremony organized by the ministry and the State Oceanic Administration in Qingdao, east China's Shandong province.

The sub, named after a mythical dragon, docked at the port of Qingdao on Monday after making record dives of more than 7,000 meters below sea level in the Pacific Ocean's Mariana Trench during a 44-day test mission.

Jiaolong completed six dives and plummeted below 7,000 meters three times, with the greatest depth being 7,062 meters. It also surveyed the undersea landscape and collected geological and biological samples.

Li noted that the submersible will have profound influences "on boosting the country's abilities to understand, protect and develop seas and transforming China into a strong maritime country."

Bidding greetings to the sub's researchers and developers, operation team crew and logistics staff, Li urged them to stick to scientific thinking and cooperation in order to achieve new heights for the country's manned sub diving cause.