Three Miles Down

From New York Times bestselling author Harry Turtledove, the modern master of alternate history, a novel of alien contact set in the tumultuous year of the Watergate scandal.
It's 1974, and Jerry Stieglitz is a grad student in marine biology at UCLA with a side gig selling short stories to science fiction magazines, just weeks away from marrying his longtime fiancée. Then his life is upended by grim-faced men from three-letter agencies who want him to join a top-secret "Project Azorian" in the middle of the north Pacific Ocean—and they really don't take "no" for an answer. Further, they're offering enough money to solve all of his immediate problems.
Joining up and swearing to secrecy, what he first learns is that Project Azorian is secretly trying to raise a sunken Russian submarine, while pretending to be harvesting undersea manganese nodules. But the dead Russian sub, while real, turns out to be a cover story as well. What's down on the ocean floor...