When the U.S. Navy ambiguously explained last month that one of its nuclear-powered submarines had rammed into an mysterious underwater object in the South China Sea last month, it sounded like the opening scene of a new disaster movie. The actual explanation, though, is slightly more mundane. According to CNN, an investigation has found that the USS Connecticut slammed into an uncharted underwater mountain. “The investigation determined USS Connecticut grounded on an uncharted seamount while operating in international waters in the Indo-Pacific region,” a 7th Fleet spokesperson told the cable news channel. The sub suffered some damage and crew members sustained minor injuries, the Navy said, but its nuclear propulsion plant was not compromised.