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In 2012, the Sansha military garrison was established to become the youngest in China. Four years on and the garrison is playing an important role in safeguarding China's southern sea border.

Far from the Chinese mainland, soldiers are training off the islands on the South China Sea. These soldiers are from the Sansha Garrison, a southernmost unit meant to protect China's sea border.

The harsh natural environment makes fitness training a lot more difficult than usual.

"The soft sand and strong water resistance makes it difficult to stand steadily. So we have to try very hard to keep balance," said Xi Zhongqiang, soldier of Sansha Garrison.

Compared to other Chinese cities, Sansha has the smallest land area. But it governs the largest sea territory.

In 2012, Sansha city was officially established to administer more than 200 islets, sandbanks and reefs in the Xisha, Zhongsha and Nansha island groups, as well as their surrounding waters.

To protect their homeland, fishermen like Ye Jun actively joined Sansha’s militia force. He has been living on Yagong island for 16 years, and is often annoyed by foreign fishing boats.

"Foreign fishing boats used explosives to bomb the fish, and this has destroyed the corals. We simply couldn't drive them away. But since we joined the militia, they haven’t been around," Ye said.

Sansha city has a three-tier law enforcement system. The militia finds and reports foreign infringement, the civil law enforcement group patrols the city, and coast guard enforces the law.

"Our core mission is to maintain the sovereignty of the South China Sea, as well as our maritime rights," said Cai Xihong, commander of Sansha Garrison.

So far, the militia has assisted in expelling hundreds of vessels who have infringed laws and regulations. And the army has patrolled over half a million nautical miles within the region.

Truly, as they say, to safeguard "the Sea of Ancestors" is their grand mission.