One of the most daring clandestine operations of World War II was the 1944 sinking of a Norwegian ferry with its cargo of "heavy water."

One of the most daring clandestine operations of World War II was the 1944 sinking of the Norwegian ferry Hydro with its cargo of "heavy water," destined for the Nazis' secret atomic bomb project. Although the mission was declared a success, no one has ever established if the special shipment was actually on board. NOVA plunges 1,300 feet beneath a remote Norwegian lake to find the answer.