Steven J. Zaloga 
Defense of Japan 1945 [PDF ebook] 

In 1945, with her fleet destroyed and her armies beaten, the only thing that stood between Japan and an Allied invasion was the numerous coastal defence positions that surrounded the islands. This is the first book to take a detailed look at the Japanese home island fortifications that were constructed during 1941 45. Utilizing diagrams, specially commissioned artwork, and sources previously unavailable in English, Steven Zaloga examines these defences in the context of a possible Allied invasion, constructing various arguments for one of the greatest ‘what if’ scenarios of World War II, and helping to explain why the Americans decided to go ahead with a nuclear option.