"Due to the confidentiality of his job, I never know when he is out on mission and when he will come back," she says with a deep sigh.

Che says that after more than 10 years of marriage, she is used to his absence from home. But she still hopes he can return more frequently for their son.

"He often says that a soldier's son should learn to be brave, but how can our son be brave enough when he, as his father, is always absent?" she says.

Though Hua spends so little time at home, he and his son still share a close bond.

Before departure, their 12-year-old son secretly put an illustrated edition of Twenty Thousand Leagues under the Sea by Jules Verne in his bag. The book is now lying on Hua's bedside.

"In Verne's novel, the world under the sea looks so romantic. However, when we are cruising under the ocean, there is only endless darkness," he says.

"The darkness deep in the ocean is where my faith and my loyalty lie," says Hua.