One ship could revolutionize submarine warfare as we know it: the USS Snarc. A robotic combat sub carrying no crew, the Snarc has proven unbeatable in sea trials. And now it has fallen into the hands of an unseen enemy.   The Snarc's first casualty: the nuclear sub carrying the son of former admiral Michael Pacino. The only man who can match wits with the Snarc, Pacino reenters the game in a high-tech underwater battle unlike any that's been fought before, one that could engulf the world in war--and bring him face-to-face with his nemesis.