The book is about the American invasion of Tarawa, an island in the Pacific and one of many that the Japanese held and needed to be cleansed of. There were around 500 pillboxes the Japanese had built and there were equally formidable defenses that had been set up.
The invasion did not at all go to plan. There were various technical errors and a far stiffer Japanese resistance they expected. The book goes into all these details and perhaps the strongest thing that stands out is the fanaticism of the Japanese defenders and their determination to kill as many Americans as they could without any concern for their own lives.
By the way, the descriptions of the deaths in this series of books can get to be rather gruesome at times,
In addition to the details of the battle there is also a list of references that the reader can consult. This entire series of books is well done.