The hardest part for submarine soldiers is uncertainty: Staying calm amid unknown waves and urgent missions

How long will the mission last? When will they return? Will they be able to contact their families? For submarine soldiers, perhaps the hardest part is uncertainty. Unpredictable waves, sudden equipment failures and urgent missions require them to stay calm and complete their mission, time and again, amid uncertainty.

Wei Chenping and Hua Linchao contributed to this story.