A dozen submarines would be an enormous group: China and Russia each only have about a dozen nuclear attack submarines, and non-nuclear submarines don't have th

A dozen submarines would be an enormous group: China and Russia each only have about a dozen nuclear attack submarines, and non-nuclear submarines don't have the undersea range to get close to a carrier battle group undetected. It would be a huge gamble to throw them all in one attack. The other problem is that the submarines would have no way to communicate without giving away their position. It would be very difficult to execute any sort of coordinated operation.