A submarine attached to a submarine flotilla with the navy under the Chinese PLA Northern Theater Command steams towards the designated area during a recent maritime training exercise. (eng.chinamil.com.cn/Photo by Zhang Nan)

A submarine attached to a submarine flotilla with the navy under the Chinese PLA Northern Theater Command steams towards the designated area during a recent maritime training exercise. (eng.chinamil.com.cn/Photo by Zhang Nan)

A submarine attached to a submarine flotilla with the navy under the Chinese PLA Northern Theater Command steams towards the designated area during a recent maritime training exercise. (eng.chinamil.com.cn/Photo by Zhang Nan)

A submarine attached to a submarine flotilla with the navy under the Chinese PLA Northern Theater Command steams towards the designated area during a recent maritime training exercise. (eng.chinamil.com.cn/Photo by Zhang Nan)