America lost two nuclear-powered submarines during the 1960s. The nuclear reactors remain underwater to this day. Phil Ochs did a song about each of them.

"Portsmouth town on the eastern shore / Where many a fine ship was born. / The Thresher was build / And the Thresher was launched / And the crew of the sworn."

More about the sinking of the Thresher. http://ussnautilus.org/blog/the-loss-of-uss-thresher-ssn-593/

More about the nuclear reactor that remains underwater. http://www.seacoastonline.com/article/20130310/NEWS/303100355