How They Became Legends (Part 5 of 8)

Continued from Part  4

Narwhal (SS-167) during the attack on Pearl Harbor. (Source:

Evolution of Threat

An appreciation of the threat posed by the Imperial Japanese Navy during the interwar years and into the Second World War offers a look at the catalyst responsible for the rapid evolution of doctrine and the challenges faced by American naval officers participating in the in the Pacific Theater of Operations. Within six hours of the attack at Pearl Harbor on December 7, 1941, the order to “execute unrestricted air and submarine warfare against Japan” was issued by the Navy Department and the departure of the USS Gudgeon marked the beginning of the first offensive patrols of American submarines in hostile waters.[1] The Imperial Japanese Navy, at that moment existed as an example of the ineffectiveness of the interwar treaties which were intended to restrict the offensive capability of the signatory nations. Earlier successes against the Russian Navy at the battle of Tsushima in May1905 placed the Imperial Japanese Navy at the forefront of naval might in the Pacific.[2] Japan’s territorial dominance was reinforced upon the conclusion of the First World War when the League of Nations granted possession of strategic islands in the Pacific in 1920, and it was the further restrictions of the Washington Naval Treaty of 1922 which restricted the production of warships in the United States which exacerbated the power balance in the Pacific.[3] Compounding the misjudgments of Japanese naval production and development, the 1930s were a decade of intelligence failures, social ignorance, and political overconfidence which minimized the threat potential posed by the Imperial Japanese Navy. Naval aviation efforts by the Japanese was repeatedly scorned as being inferior and incapable of direct comparison with British and American aviation efforts. Similarly, the contemporary racial assumptions erroneously discredited Japanese operational and doctrinal abilities. Most importantly, however, was the official dismissal that Japanese aggression and technology was easily estimated, predictable, and would be easily countered by economic pressures and superior Allied naval capabilities. American intelligence before the Japanese attack on Pearl Harbor maintained an unfounded and biased view of the capabilities, while some naval personnel fully understood the potential threat and ability of the Japanese military forces.[4]

The development and implementation of effective intelligence efforts in the last few years of peace provided the first indications of Japanese intentions and would later prove to be vital in the persecution of Japan’s naval and maritime forces. The slow process of deciphering of the Japanese diplomatic and military codes and the consolidation of intelligence assets in key locations around the Pacific provided the first solid results in 1940 with the deciphering of JN-25 – the main naval code used by the Imperial Japanese Navy.[5] Despite this intelligence victory, the inability of the United States to sufficiently recognize, disseminate, and act upon the indications present in the deciphered political and military communications constituted only one part of a series of missed, or neglected opportunities.[6] The advancements in Japanese naval technology and doctrine placed the United States Navy at a severe disadvantage prior to the commencement of hostilities in 1941. Reliance on advancements in submarine and torpedo bomber efforts during the interwar years strongly complimented the development of long-range and potent “Long Lance” torpedoes supported the Japanese military intentions of increasing the engagement range of American battleships, thus negating the vaunted abilities of these key warships.[7]

Finally, Japanese anti-submarine warfare suffered significant developmental stagnation during the interwar years. The pre-war emphasis of anti-submarine assets primarily assigned to fleet screening, or protection duties, placed the Imperial Japanese Navy at a severe disadvantage at the beginning of the Second World War.[8] For those warships designated to be the prime defenders against the threat posed by American submarines, there were several factors which prevented their effectiveness throughout the war. Sonar, the ability to use sound waves to detect submerged objects or vessels, was a relatively new technology for the Imperial Japanese Navy, and though their anti-submarine vessels were fitted with basic sonar equipment, they lacked the ability to accurately determine the depth of enemy submarines, Japanese employment of depth charges relied on saturation of a target area where the identity of an enemy submarine was confirmed. Assuming American submarine construction prevented operational depths to exceed 400 feet, Japanese depth charges were designed with this requirement as the maximum effective depth.[9] Likewise, bathythermographs – equipment necessary in determining the presence of a underwater density layers which could hinder anti-submarine effort – were not available, later proving to be a significant  contributing factor which compounded the sonar technician and screen commanders ignorance of the environmental factors which influenced the tactical situation.[10] Lastly, trained sonar operators were a limited resource within the Imperial Japanese Navy. The enlisted and officer courses were no more than 7 months long, with very few officers attending and finishing the course; however, the facilities for training were limited and actual practice was conducted without the benefit of static land-based simulators.[11] Despite these nationally-induced limitations, the threat posed by Japanese anti-submarine efforts manifested a direct and capable threat to American submarines during the war and obligated the skippers to adapt through necessity to survive.

Amatsukaze II.jpg
IJN Amatsukaze 17Oct1940. (Source:


[1] Blair, 84.

[2] “The Development of Japanese Sea Power – ‘Know Your Enemy!’,”, 1945, accessed June 25, 2017,, 23.

[3] Matloff,2.

[4] McBride, 202.

[5] Blair 54-53.

[6] Blair, 67.

[7] McBride, 172, 202.

[8] United States Navy, Japanese Anti-Submarine Warfare, (Washington D.C.: Government Printing Office, 1946), accessed June 25, 2017,, 7.

[9] Japanese Anti-Submarine Warfare, 11-12.

[10] Ibid., 41.

[11] Ibid., 43.


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