Chinese sub pops up in middle of U.S. Navy exercise

When the U.S. Navy deploys a battle fleet on exercises, it takes the security of its aircraft carriers very seriously indeed. At least a dozen warships provide a physical guard while the technical wizardry of the world's only military superpower offers an invisible shield to detect and deter any intruders. That is the theory. Or, rather, was the theory. American military chiefs have been left dumbstruck by an undetected Chinese submarine popping up at the heart of a recent Pacific exercise and close to the vast U.S.S. Kitty Hawk - a 1,000ft supercarrier with 4,500 personnel on board. By the time it surfaced the 160ft Song Class diesel-electric attack submarine is understood to have sailed within viable range for launching torpedoes or missiles at the carrier. Full story...

This is not the first time fleets have been surprised by diesel electric subs. Here is a story from a South Africa vs NATO exercise. I also vaguely remember reading about a Dutch sub doing the same trick a few years ago, though I can't find a source.