By Justin Pyke
Editorial Note: In the first of a three-part article, Justin Pyke examines American intelligence assessments of Japanese air power during the inter-war years. This first part examines issues in the 1920s.
In December 1941 Japan launched a campaign of rapid conquest against British, American, and Dutch possessions throughout the Asia-Pacific region. The Imperial Japanese Army Air Service (IJAAS) and Imperial Japanese Navy Air Service (IJNAS) proved critical to the success of these early campaigns. Although American authorities identified Japan as a primary rival after 1918 and focused most of their intelligence gathering efforts on the East Asian nation, they failed to appreciate the threat posed by Japanese air power in 1941. This failure was not as simplistic as the old historiography portrays. Instead, intelligence assessments of Japanese air power passed through three distinct phases. During the 1920s, American observers maintained an accurate picture of Japanese capabilities. Japan was largely an open society, and its air services depended on Western assistance, meaning the Americans were able to track major developments. The early and mid-1930s was a transition period from the openness of the 1920s to the extreme secrecy that characterised the period from 1937 onward. With the start of the war in China, the Americans were almost completely in the dark regarding assessments of the Japanese air services’ technology, tactics, and personnel. One thing that remained consistent from 1920-41 was American observers accurately assessed the strategic and industrial limits of Japan’s air power. Success with these higher level assessments ultimately mattered more than the mistakes made assessing technology and tactics.
Throughout the 1920s Japan worked rapidly to catch up with the developments of Western powers in the field of military aviation. During this period, American intelligence assessments remained accurate at all levels, from personnel, tactics, and technology to industry and the scarcity of raw resources. American observers quickly identified Japan’s heavy reliance on foreign assistance and the weakness of its aviation industry, while the quality and quantity of Japanese aviation personnel and aircraft were carefully tracked. As throughout the entire inter-war period, the assessments primarily addressed Japan’s ability to wage a protracted war of attrition in the air, rather than to focus on tactical and technical capability.
The accuracy of American assessments in the 1920s was due in large part to openness within Japan. Letters were constantly exchanged between the American naval attaché and the Japanese Navy Ministry. The letters requested information about the IJNAS, such as its organisation, the numbers of available aircraft, and the number of existing and planned naval air stations. The Navy Ministry answered these letters in full. The ease with which the naval attaché obtained large amounts of information through direct communication with the Navy Ministry was remarkable, but the openness of the Japanese was not limited to such communication. Tours of aircraft manufacturing facilities and air stations were also open and casual. The Americans were not rushed through important areas. The level of detail in an extensive report on Japanese aircraft factories from 1925 was typical and revealed lax Japanese information security. Minor technical details and factory layouts were abundantly described throughout the report, revealing the high level of access Americans had at the facilities. Japanese workmen and designers were extremely forthcoming when asked direct questions about their work.
Japan’s reliance on foreign assistance allowed the Americans to keep pace with its technological and industrial advances. A report in 1924 stated that Japan always sought out the best foreign designed aircraft that it could purchase, and copied these models, along with the means to produce them. The air services were also modelled after what the Japanese thought was the most advanced foreign air forces. For example, the IJNAS relied on British assistance regarding industrial practices, aviation technology, personnel training, and tactics. The American naval attaché constantly emphasised the Japanese inability to design and build aircraft without extensive foreign aid. After inspecting the aircraft factories, he concluded that they had yet to produce any indigenously designed aircraft or engines ‘of any value whatsoever.’ A general summary from 1927 noted that all Japanese aircraft were of foreign design and that these aircraft were underpowered and inferior to contemporary American designs. This claim was an overstatement, but the number of indigenous Japanese military designs remained very small throughout the 1920s. The motif of Japanese unoriginality would persist through to the beginning of the Pacific War, long after it had ceased to be true. In the 1920s, however, Japan did seek to develop its air power by following in the footsteps of the world leaders.
The inferior production methods of Japan’s major aircraft manufacturers were also highlighted. One such report noted that most of the machine tools in the factories were of American manufacture and the machine shops themselves were crowded, which led to inefficiency within the production process. Production was prolonged, particularly when a factory was ordered to manufacture new types of aircraft. During this process, foreign workmen were always employed to ensure a smoother transition. The Japanese aviation industry’s inability to rapidly turn existing factories over to produce new models of aircraft persisted into the Pacific War. It undermined Japan’s ability to keep pace both qualitatively and quantitatively with their Western foes. For example, the J2M Navy Interceptor Fighter (Raiden/‘Jack’) first flew nearly three months ahead of the F6F Hellcat prototype’s first flight. Despite this, the first production Hellcat was completed in the same month that the J2M had only just been accepted for serial production. Six months later only 14 J2Ms had been delivered at a time when Hellcats leapt off the American production lines.
The opinion of Japanese personnel was generally low but remained balanced. A 1926 memorandum held Japanese airmen and officers in high regard, referring to them as ‘well disciplined.’ Most pilots were described as ‘good,’ while the work of the mechanics was deemed ‘most praiseworthy.’ The naval attaché’s assessments of Japanese pilots were more critical. One report concluded that the Japanese have a ‘fair ability’ as pilots, but rated them poorly in all around efficiency. The British aviators who had trained the IJNAS in the early 1920s informed the Americans of their low opinion of Japanese personnel, and this view was shared by Colonel Jacques-Paul Faure, head of the French Military Aviation Mission to Japan that had trained the IJAAS’ pilots. A major 1928 report on Japanese aviation viewed mechanics within the Japanese air services as poor, although civilians brought in to help the military were good. Conspicuous by its absence was any notion of the inferiority of the Japanese race despite the criticism levelled against Japanese personnel.
A handful of reports did, however, attribute personnel deficiencies to the national characteristics, or national stereotypes, of the Japanese people. One assessment stated that:
[t]he Japanese is not a natural flyer and rarely loves flying for its own sake. Neither is he a natural mechanic, nor has he any tradition of trained mechanics behind him.
While it is easy to dismiss this statement as racist or irrational, it did contain some truth. The Japanese air services had a chronic shortage of trained mechanics, partly because Japan was not a fully industrialised nation like the United States or Great Britain. The Japanese economy, despite massive leaps since the Meiji Restoration, continued to operate ‘with one foot in the nineteenth century.’ Once again, the quality of Japanese pilots was called into question, but the report concluded that if American pilots were considered ‘very good,’ the Japanese were rated ‘good.’ This statement made it clear that the Japanese were inferior to their western counterparts, but it was hardly irrational or unfair.
The most noteworthy weaknesses that the Americans identified regarding Japanese aviation personnel were the lack of pilot training and reserves. In an information bulletin detailing the Japanese Diet’s 1924 budget for naval aviation, the naval attaché noted that the IJNAS had no reserve personnel at all. Another report stated that ‘there are three schools of aviation, but only one [sic] army flying training school,’ and went on to detail the number of pilots available to Japan. The 1927 general summary of the Japanese air services questioned the flying experience of the officers, and described the flying seen in Japan as ‘characterized by timidity and one could not help but feel that dash and spirit were lacking.’ The report concluded that the IJAAS and IJNAS were at:
[a]n elementary stage of development. None of them are capable of combat with well developed aviation, considering factors other than equipment.
Taken as a whole, American intelligence assessments of Japanese air power during the 1920s were highly accurate from the strategic and industrial spheres down to the tactical and technological level. Lax information security measures within Japan provided American observers with a remarkable level of freedom. American reports assessed the ability of Japan to fight a protracted war in the air, where aircraft production figures, industrial efficiency, innovative aircraft design, strong pilot training programs, and sizeable pilot reserves were critical to achieving success. The correct conclusion was Japan did not yet possess air power that could seriously threaten the Western powers, but this would begin to change in the 1930s.
Header Image: A Nakajima A2N carrier borne fighter that first flew at the end of the 1920s. (Source: Wikimedia)
 For examples of the old view regarding American intelligence assessments of Japan, see: John W. Dower, War without Mercy: Race and Power in the Pacific War (New York: Pantheon Books, 1986); David Kahn, ‘United States Views of Germany and Japan in 1941,’ in Ernest R. May (ed.), Knowing One’s Enemies: Intelligence Assessment before the Two World Wars (Princeton: Princeton University Press, 1986).
 A-1-u 17242, Letter to Captain K. Terashima, I.J.N., January 27 1925, Naval Attaché Reports, 1886-1939, Box 142, Record Group [RG] 38, National Archives and Records Administration [NA], Washington, D.C.; A-1-u 17242, Information on Air Services, March 5 1926, Naval Attaché Reports, 1886-1939, Box 142, RG 38, NA; A-1-u 17242, Letter to Mr McClaran, February 10 1925, Naval Attaché Reports, 1886-1939, Box 142, RG 38, NA.
 A-1-u 17242, Visit to Aircraft Factories, May 15, 1925, Naval Attaché Reports, 1886-1939, Box 142, RG 38, NA.
 2085-630, Extracts from Report of Inspection of United States Possessions in the Pacific and Java, Singapore, India, Siam, China, & Japan, October 24, 1924, US Military Intelligence Reports, Japan, 1918-1941, Reel 28, University Press of America, 1.
 Mark R. Peattie, Sunburst: The Rise of Japanese Naval Air Power, 1909-1941 (Annapolis: Naval Institute Press, 2001), pp. 17-20; Jonathan Parkinson, ‘HIJMS Wakamiya and the Early Development of Japanese Naval Air Power,’ The Mariner’s Mirror, 99:3 (2013), pp. 318-321. Also see: John Ferris, ‘A British ‘Unofficial’ Aviation Mission and Japanese Naval Developments, 1919-1929,’ Journal of Strategic Studies, 5:3 (1982), pp. 416-39.
 A-1-u 17242, Japanese Air Strength, May 5, 1925, Naval Attaché Reports, 1886-1939, Box 142, RG 38, NA, 3.
 2085-663, General Summary Japanese Air Service, June 1, 1927, US Military Intelligence Reports, Japan, 1918-1941, Reel 28, University Press of America, 8.
 See: Robert C. Mikesh and Shorzoe Abe, Japanese Aircraft, 1910-1941 (Annapolis: Naval Institute Press, 1990).
 A-1-u 17242, Visit to Aircraft Factories, 1, 8.
 Fighter Combat Comparisons No. 1: Grumman F6F-5 Hellcat vs. Mitsubishi J2M3 Model 21 Raiden (‘Jack’) (Teaneck: Tacitus Publications, 1989), p. 13.
 2085-647, Memorandum for Major Baldwin, September 30, 1926, US Military Intelligence Reports, Japan, 1918-1941, Reel 28, University Press of America, 3, 6.
 A-1-u 17242, Japanese Air Strength, 3.
 Thomas G. Mahnken, Uncovering Ways of War: U.S. Intelligence and Foreign Military Innovation, 1918-1941 (Ithaca: Cornell University Press, 2002), p. 73; A-1-u 17242, Aviation, July 21, 1925, Naval Attaché Reports, 1886-1939, Box 142, RG 38, NA, 3.
 2085-784, Report of Major W. B. Duty, September 20, 1928, US Military Intelligence Reports, Japan, 1918-1941, Reel 29, University Press of America, 83.
 2085-748, Japanese Aviation: Army, Navy, Civil, July 20, 1927, US Military Intelligence Reports, Japan, 1918-1941, Reel 29, University Press of America, 2.
 Eric M. Bergerud, Fire in the Sky: The Air War in the South Pacific (New York: Basic Books, 2009), p. 17.
 2085-748, Japanese Aviation: Army, Navy, Civil, 2.
 A-1-u 17242, Data for Congressional Hearing; Additional Detailed Information on Air Services, February 9, 1925, Naval Attaché Reports, 1886-1939, Box 142, RG 38, NA, 2.
 2085-719, Information as to Japanese Aviation, February 9, 1927, US Military Intelligence Reports, Japan, 1918-1941, Reel 28, University Press of America.
 2085-663, General Summary Japanese Air Service, 3, 7.