It's really well done. She interviewed people going back to the first US subs and recounted their first hand experiences. A lot of the stuff is declassified now, but tells stories of things which were highly covert at the time. The first chapter isn't wowing, but it picks up steam quickly after that. It is a living history of subs, how they evolved and how they were used. Won't spoil anything, but there are some eye opening segments told by the men who lived it. Plus it sheds light on how the different branches of government hide things from each other and inevitably step on each other's toes.

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