The C.S.S. Virginia (Merrimac) was blown up in the James River to prevent her being captured.
The U.S.S. Monitor was being towed southward to be used in the campaign against Fort Fisher when she and the towing vessel were caught in a storm off Cape Hatteras. The Monitor took on water and sank. She is now sitting on the bottom and is, to my knowlege, the United States' first official underwater National Historic Site.