North Korea is possibly building a new submarine that can fire ballistic missiles, according to South Korean and U.S. defense officials, Friday. This could be a serious security threat to the United States as the submarine-launched ballistic missiles (SLBM) may reach as far as the U.S. mainland. "[SLBM technology] changes the defense equation in terms of where the origin could be," U.S. Undersecretary of Defense for Policy John Rood said Wednesday (local time) in a Senate hearing. The SLBMs are considered more threatening weapons than intercontinental ballistic missiles (ICBM), as they are harder to detect and increase the regime's strike...