On Jan. 8th 2005 the Sanfrancisco, a Los Angelos class attack submarine ran into an underwater mountain that was uncharted. These pictures show the external damage. One man was killed and 24 injured. It was later determined that the navigation team had not followed proper procedures and that they consistantly scored low during inspections of their abilitys. Although the commander was not cited as being to blame he was permanently grounded as a result of the accident. Thats the Navy! The damage exceeded 20 million dollars. Three ballast tanks were inop as well as a crushed sonar dome and nose cone. The following link has much good info on the use of sonar and how a state of the art SSN could possibly run into something in the ocean.
http://wiki.answers.com/Q/How_do_submar ... o_navigate