The Third Fleet maintained its station along the Chine Coast and up the Yangtze River. This undoubtedly represented a blockade of China’s ports, if the blockade was not actually taking place at that time.
The Third Fleet had many more ships than the old China patrols in 1930, and this new function of the Third Fleet was a departure from the 1930 Maneuvers. Later on (1936 and thereafter), when the Third Fleet began covering and assisting landing forces in China, the reason for its earlier training and diversion to Chinese waters became apparent.
The First and Second Fleets escorted the troop transports and covered the operations of the “Combined Landing Force” thus taking over the duties performed by the Third Fleet in 1930. The First and Second Fleets assembled at Yuyu Bay during the week 5 to 12 June 1933. On 24 June they moved to the Sasebo Naval Base. On 29 June they advanced to Formosa by the Saddle Islands, the First Fleet going to Bako, the Second Fleet to Takao, stopping at Bako enroute. On 13 July both Fleets departed for Palau, and the so called strategic phase of the problem began on that date. The First and Second Fleets entered Kossol Channel on 18 July and remained in that vicinity up to 30 July, when they moved to Ulithi. Landing exercises were held during this period, undoubtedly simulating landings on Luzon. The First and Second fleet spent 14 days at Ulithi conducting numerous drills and exercises, and representing strategic deployment against the U.S. Fleet. This concluded the strategic phase of the exercises.
In the tactical phase of the maneuvers, the First and Second fleets became the Battle and Scouting Fleets of the BLUE (or United States) Fleet, and the Japanese Base Force became the U.S. Fleet Base Force. It was assumed that the U.S. Fleet had steamed westward from Pearl Harbor, held or recaptured Guam and had captured Japanese bases in the Marianas. From these advanced bases, the BLUE Fleet launched an “all-out” attack on Japan proper. Meanwhile the defending Fourth Fleet, known as the RED Fleet and representing the entire Combined Fleet, had occupied advanced positions in the Bonin Islands. The opposing forces made contact and engaged in the final battle about 400 miles southeast of the Bonin Island on 18 August. The Commander-in-Chief, Combined Fleet, aboard the MUTSU, commanded the BLUE Fleet. According to press release, the Emperor of Japan, aboard the HAGATO, personally commanded the RED Fleet.
The work of the Base Force, operating directly under the Commander-in-Chief, Combined Fleet, is of particular interest in two respects. First, it established temporary air bases at Chichijima, Iwo Jima, Pagan, and Saipan. These air bases were expanded into permanent establishments after the maneuvers. Seaplanes were flown from Yoltosuka to Saipan. This was a long hop for those days and much better than anything the U.S. Navy had credited the Japanese Navy with being able to do. It was apparent that Japan had developed a strange breed of aviators who shunned publicity.
U.S. AND JAPANESE HFDF
The Base Force also established high-frequency direction finders during the period May to July 1933, as follows:
No. 4 – Chichijima
No. 5 – Iwo Jima
No. 6 – Saipan
No. 7 – Pagan
These stations worked with No. 1, at Yokosuka during the maneuvers and remained in commission thereafter. No. 2 D/F, at Sasebo, and No. 3, at Hozan, did not participate in the maneuvers or were not heard by our people. The direction finders were calibrated with the assistance of Base Force minesweepers and tracked Japanese patrol planes for exercise. They also took bearings on the U.S.S. HOUSTON, anchored at Tsingtao, China, on a frequency of 12,820 kc., and on the U.S.S. MONOCACY, in Shanghai, on a frequency of 335 kc.
These early bearings were not particularly accurate, but neither were ours when we got high frequency direction finders installed at Guam and Cavite, four years later. By 1934 the Japanese direction finders could be considered fairly accurate and reliable. Later on (about 1940), we learned from intercepted messages that the Japanese direction finders had tracked three U.S. cruisers (on a secret mission) all the way from Pearl Harbor to Singapore, and had predicted their destination and time of arrival 24 hours in advance. The significance of these Japanese D/F installations lies in the fact that in 1933 some of the U.S. Navy’s radio engineers were claiming that the high frequency direction finder was technically impossible, and that Naval Operations was wasting time and money by its insistence on the development of high frequency D/F apparatus. Forty seven messages intercepted during the 1933 Maneuvers, to say nothing of countless messages intercepted and decrypted during later years, proved these people wrong. Fortified with this secret knowledge, we redoubled our pressure on the Radio Division (officially, unofficially, and through the Radio Materiel Improvement Plan) until we finally got the apparatus we needed. It was not until 1939, however, that our D/F stations in the Pacific Ocean, even approached those of the Japanese as regards number and quality of apparatus; and it was a year later before our D/F operators were comparable with the Japanese in skill and experience. At the present time we have outstripped the Japanese, as well as other nations, in the quality of D/F apparatus and in skill of “tracking.”
JAPANESE COMMUNICATION SECURITY
The Japanese Navy was making great strides in Communication Security; a bad omen for us. In the 1930 Maneuvers only one code system and one system of ‘ Secret Radio Calls were used, while most of the messages were sent with “Service Address” Our “Cryptographic Intelligence” phase of the 1933 Maneuvers entailed the solution of three codes, nine cipher systems, seven secret call lists, and four secret address systems, plus the use of one partially solved code (the “Blue Book”), and required a total of three years. Each succeeding year increased the bulk and difficulty of our task. Our R.I. Organization was adequate in skill but not in numbers.
The success of “traffic analysis” in giving a picture of the 1933 Maneuvers, without the information obtained later from decryption, completely sold the idea of Radio Intelligence to ADM Upham. The lessons of the 1933 Maneuvers were taken seriously and the following recommendations submitted in CINCAF secret letter CF 283 dated 7 March 1934:
(a) Locate one intercept unit in the Ultimate Defense Area (of Manila Bay) so that it can function without interruption upon the outbreak of war. (This was done in February 1935).
(b) Establish a decrypting center in connection with the intercept station in the Ultimate Defense Area. (This was done in July 1934).
(c) Equip all stations with suitable (i .e., high frequency) long-range direction-finding apparatus and the best obtainable receivers. (This was completed by December 1938).
(d) Provide sufficient intercept operators. (The number serving on the Asiatic
Station was gradually increased as more men became available, and all personnel were finally merged in one big station, except for a minor unit at Guam.)
(e) Provide at least two cryptanalysts, one translator, and two clerks for analysis of intercept material. (This was completed by the end of 1935.)
(f) Conduct intercept activities….with the mission of preventing surprise attack. (This had been our concept since 1924.)
By L. F. Safford, Captain, USN
Source: CRYPTOLOG NCVA