"The Unit" (9 p.m., CBS): In an absorbing rerun, our heroes take on a grueling exercise in which they are forced to play the roles of prisoners of war. Can they stand up to all the physical torture

"The Unit" (9 p.m., CBS): In an absorbing rerun, our heroes take on a grueling exercise in which they are forced to play the roles of prisoners of war. Can they stand up to all the physical torture and personal humiliation?
"Nature: War Wrecks of the Coral Seas" (10 p.m., PBS): Ghostly hulks have become teeming centers of life, serving as reefs upon which fantastic mini-ecologies now thrive.