The fact that Japanese submarines were relatively ineffective in World War II, particularly when compared with those of the Americans and Germans, has long been acknowledged, but the reasons cited for their shortcomings have been varied and based on limited information. Now, a noted American naval historian and a Japanese mariner have painstakingly recorded and evaluated a diverse array of material - much of it only recently declassified - and drawn authoritative new conclusions. The focus of their examination is American wartime intercepts of secret Japanese radio messages and official Japanese sources. This study reaches back to the development of the first Japanese 103-ton Holland-type submersible craft in 1905 and continues through the 1945 surrender of the largest submarine in the world, the 5,300-ton I-400 that carried three airplanes. Submarine weapons, equipment, personnel, and shore support systems are discussed first in the context of Japanese naval preparations for war, and later during the attrition of war. The authors fully analyze a series of successes and missed opportunities in submarine operations in the Pacific, Indian, and Atlantic Oceans, from the California coast to German-occupied France. The appendixes include lists of Japanese submarine losses and biographies of key submarine officers with the rank of lieutenant commander and above. Nineteen rare illustrations and fourteen specially commissioned operational maps enhance the text. Specialists and World War II submarine buffs alike will appreciate the efforts undertaken by these two men.