Just before this book came out, Jack and i talked at an SF convention, and he told me a few things.
According to him, at that time, Universal's plans for the next "Jaws" film were that it was to be a prequel, teeling the story of the "Indianopolis", with Quint being one of the survivors, thus setting up his lieflong hatred and fascination with sharks.
He also talked about how his research had revealed the shameful way that the Navy had treated the true heroes of the disaster, and that at least one person who had received a medal for his actions had, in fact, done something shameful and stupid that the Navy had covered up. And he said he named this person by name in the book. "And, if he wants to sue, I have the documentation to prove every word I said," he said, obviously hoping that the guy would sue.
Been years since i read it, but as i recall, the early part of the book involves a visit from the FBI to the New York offices of publsiher Street & Smith, to question John W. Campbell, Jr, editor of "Astounding) Science Fiction" (later "Analog") about a piece published in the magazine that basically described with some accuracy the enriched-uranium atomic bomb that the Manhattan Project was even then developing in secret.
This is a true story. Writer Cleve Cartmill had, strictly as a theoretical exercise, worked out how such a device might operate ("atomic" bombs ahd been staples of SF for some time). (Campbell convinced them that ordering the magazine kept off news stands after subscribers' and library copies had already been mailed might well cause someone to wonder why and lead to calling attention to the very item the FBI were trying to suppress...)