With a glimpse of the country's fleet of nuclear submarine for the first time, these submarines have participated in multiple training and drills, simulating actual combat. Using domestically designed techniques, the fleet has also sets numerous Chinese records.

For the first time in 42 years, China's nuclear submarine fleet has been revealed. The submarines are now taking part in a military drill in China. Equipped with the latest domestic designed navigation system, the submarines have achieved a major breakthrough in terms of the distance and depth travelled.

"This drill is different from previous ones, because there are more warships participating..including destroyers, frigates, supply ships and nuclear submarine. Also, we don't know the whole plan of the drill, so we need to respond quickly and promptly," said Liu Yunhai, Captain, China Nuclear Submarine.

Working on the submarine is challenging both physically and psychologically. And for these submariners, they work under water for months, without a glimpse of sunshine.

"We can not distinguish day or night under water. After days of consecutive work, dizziness, insomnia, no appetite, it hits us, and it is just beyond us," said a submariner Hu Junhua.

It's the passion and responsibility of protecting their motherland that keeps them working.

"We believe that every sail and every dive we have made is a journey to better protect the country," said the Submarine Base Commander Gao Feng.

The fleet has made many Chinese records. It fired China's first rocket underwater. It also set a record for the deepest dive. Over the past 42 years, this team of submariners has sailed over millions of nautical miles, without any accidents.