From the OP article...
article excerpts:
Years ago, the US Pacific fleet used to mock Chinese submarines for being too noisy and too easy to detect, but that changed when they successfully tailed US aircraft carriers in the East China Sea in recent years.
In 2006, a People’s Liberation Army Navy Type 039 (Song class) diesel-electric submarine surfaced within five nautical miles (9km) of the USS Kitty Hawk when the aircraft carrier was on a training exercise in the East China Sea between Japan and Taiwan.
And last October, officers on board the aircraft carrier USS Ronald Reagan were shocked when they discovered that a People’s Liberation Army Navy attack submarine had sailed “very close” to it near Japanese waters, the Washington Free Beacon reported, citing American defence officials.
A few days after that close encounter with the PLA, the Pentagon sent the destroyer USS Lassen to sail within 12 nautical miles of Subi Reef, one of seven man-made Chinese islands in the Spratly Islands in the South China Sea on a so-called freedom of navigation operation. Washington and Beijing pointed fingers at each other for escalating tension and militarising the disputed waters, which are claimed wholly or in part by mainland China, Vietnam, the Philippines, Malaysia, Brunei and Taiwan.
http://www.scmp.com/news/china/diplomacy-defence/article/1985071/china-and-us-silent-fight-supremacy-beneath-waves-south