Spy Sub is the tale of a top-secret submarine named Halibut that lowered miles and miles of special cable along the bottom of the Pacific Ocean in order to investigate a sunken Soviet sub. The mission was such a success that the Halibut itself received a Presidential medal in a secret ceremony. It's a true story, even the part about the sub getting a medal. Roger C. Dunham, a nuclear-reactor operator on board the Halibut during the mission, provides a firsthand account of an aspect of Cold War espionage that has only recently begun to surface. To this day, the Pentagon refuses to acknowledge such missions, in all likelihood because they are still going…