The first phase of the 1930 Maneuvers (from the U.S. Navy standpoint) was radio interception at Guam. The operators knew from the sudden increase in traffic on 18 May 1930 and the percentage of code messages on Japanese naval circuits that “something was up.”

They went to watchstand-watch and maintained this condition for the duration of the maneuvers except during conditions of peak load, when they manned spare receivers during their “rest periods.” The Commandant at Guam was kept informed of the situation and gave general encouragement to the men. Traffic steadily increased in volume, reaching a peak near the end of the maneuvers on 13 June. A portion of the Japanese Fleet approached so close to Guam that I.F. transmissions could be intercepted and key clicks could be heard. The only direction finder on Guam was obsolete, inoperative, and located ten miles from the intercept station: it had no crew and no bearings were taken. By traffic analysis the operators estimated that this squadron spent a few days at Saipan, which was verified by a native employee in the Commandant’s office who was visiting relatives on Saipan at that time.

A complete report of the maneuvers, with H.F. intercept logs and I.F. intercept logs as enclosures, was forwarded by officer courier; this was the Navy Departments first intimation that these maneuvers had taken place. The commandant at Guam apparently believed that the Navy Department was so well informed and did not consider it necessary to report this fact by dispatch; in fact, he complained that the Department had failed to give him advance notice so that suitable preparations could be made. The Naval Attaché, Tokyo, reported that the Japanese Navy was engaged in routine training exercises during this period.

The first Officer in charge of the Navy Code and Signal Section (a forerunner of the Naval Security Group) and inventor of the Navy Cipher Box in WWI, VADM Willson wrote the wartime signal book. His other assignments included command of several ships. Duty at the Naval War College, commander of several destroyer divisions, Naval Attaché duties, and Superintendent of the U.S. Naval Academy.  In 1942 he became Deputy Commander in Chief, U.S. Fleet. Later in WWII he served as a member of the American Delegation at the Dumbarton Oaks conference and as a military advisor at the United Nations Conference in San Francisco.

The intercept station at Guam had been established the year before and was at that time our largest station, with a complement of nine men. The years’ time had been sufficient to install an efficient array of antennas and get the personnel working smoothly. The most experienced man at the station, CRM Lyon; had had two years’ previous duty at the intercept station at Shanghai. The other eight men had been trained by CRM Kidder in the first and second classes of the Intercept Operators School at the Navy Department. The Chief Radioman-in-Charge (Reynolds) is now on the retired list, and two men have been returned to general service. The remainder, Gunn, Vandenberg, Lyon, Daniels, and Goodwin, all with temporary ranks of LTJG, plus Lusk with the rank of CRE, are all performing R.I. duty, and are the backbone of our present Intercept Organization. From this time on we felt great confidence in our R.I. operators but realized that our largest intercept station should not be on an undefended island which could be captured on M-Day.

The second phase (for us) was decryption, which was done entirely at the Navy Department. The Japanese introduced a new cipher system for these maneuvers plus a daily change of key, but used the good old “Red Book.” previously referred to. It was a perfect setup for our small Decrypting Unit. All hands turned to on these messages, Mrs. Driscoll got the first break as usual, and the various daily keys were solved without too much effort.

Every intercepted message was decrypted and eventually translated. The translation presented the greatest difficulty of all, due to the pressure of work on our only translator (Dr. Haworth), although the simpler type of routine messages did not require a student of Japanese. Much of this work was done by LT Wenger, who was under instruction in cryptanalysis at that time.

The work of solving these cipher systems and decrypting the messages was one of the most interesting duties ever under taken by the section. We were literally exploring virgin territory and no one in the U.S. Navy had the slightest idea as to the professional concepts of the Japanese Navy. The first message, chronologically, was a simulated warning (sent in secret code) that hostilities between the United States and Japan were imminent and ordered a complete mobilization. Thereafter, messages ticked off in regular order as presumably laid down in the Japanese war plans. Dummy messages (in code) went on the air, increasing the traffic on point-to-point circuits about five times its normal amount. These dummy messages were all in the nature of propaganda and “pep talks” to remind the Japanese of their glorious past, their duty to their Emperor, and the joy of dying for one’s own country. Other stations attempted propaganda directed at the British, Chinese, and Filipinos; only the Japanese sent it in secret code and used it for dummy traffic.

The second message of importance announced the simulated declaration of war and directed all fleets to proceed in accordance with plan. The capture of Guam was announced at an early date, followed in due course by the capture of the Philippines. Simulated air raids on Tokyo from the LEXINGTON and SARATOGA were reported, and district patrol craft sank U.S. submarines. The climax of the maneuvers was the “constructive” defeat inflicted upon the U.S. Fleet, there being no actual fleet action. From the tone and wording of these messages there is no doubt that in 1930 the Japanese Navy felt itself capable of defeating the U.S. Navy in Japanese home waters.

LT Wenger, shown as a Captain

The third phase (for us) was the reconstruction of the maneuvers. Preliminary work was done, as I remember, by LT Wenger, but the final analysis was made by. CAPT R.E. Ingersoll, then serving in the War Plans Division. CAPT Ingersoll worked about six weeks reconstructing the maneuvers, checking reports and orders, verifying translations, and estimating the probable Japanese War Plans. The most astonishing discovery was that the Japanese had a very good idea of American War Plans, as annually rehearsed at the Army and Navy War Colleges, and had taken suitable measures to take a devastating toll of attrition during our steam-roller advance to the relief of the Philippines. It is my understanding as a result of CAPT Ingersoll’s studies, and at least we knew the “enemy’s” intentions.


The 1929 organization of the Japanese Navy consisted of the Combined Fleet and Naval District Forces. The Combined Fleet consisted of the First Fleet (roughly

Corresponding to the U.S. Battle Fleet), the Second Fleet (roughly Corresponding to the U.S. Scouting Fleet), and the Third Fleet which consisted of a few gunboats and overage destroyers patrolling the China coast. The war maneuvers heavily reinforced the Third Fleet to permit a blockage of the China coast and created a large Fourth Fleet, based at Bako, which covered the (constructive) “Philippine Expeditionary Force” assembled in Formosa. Every island in the Japanese Mandate was a potential air base and submarine base, particularly the chain that extended from the Bonin Islands to Saipan. The Second Fleet was a protective screen which took station in the above-mentioned chain; made contact with the U.S. Fleet and retired before it, making nightly torpedo attacks. We even had the formation, stations, and exact composition of one of the Japanese scouting lines. The First Fleet was a striking force which remained in the vicinity of the Inland Sea until the U.S. Fleet had been worn out by night attacks, decimated by attrition, and considered ready for the knockout punch. Overall, coordination of effort was affected by the Commander-in-Chief, Combined Fleet, making extensive use of the excellent Japanese naval communication organization spread out through the Japanese Empire and Mandated Islands. This is interesting from a communication viewpoint because the Japanese Fleet made much more use of shore radio stations than we did at that time.

The “U.S. Fleet” was partly constructive and partly simulated by a few auxiliaries. The entire Combined Fleet operated as an entity under its own Commander-in-Chief. In our own maneuvers, it may be recalled, the U.S. Fleet always was divided into opposing forces while its Commander-in-Chief was related to the status of Chief Umpire and Observer. The fact that these maneuvers were a rehearsal of war plans is hinted in a secret message sent by the Japanese Naval Attaché, which I quote from memory:

“I asked Admiral Pratt (the C.N.O.) three times what was the strategic significance of Joint Army-Navy Maneuvers in Panama and each time he told me that they had no strategic significance. His reply may not be the truth but I know that I am reporting it correctly because I asked him three times and the answer each time was that the U.S. Fleet Maneuvers were just tactical exercises with no strategic significance.”

Apparently a Japanese naval officer could not comprehend large-scale maneuvers that did not simulate a probable strategic situation.

The Japanese Navy did not demobilize to its 1929 level after the 1930 Maneuvers.

The older vessels and auxiliaries were placed in reserve but none were decommissioned. Our R.I. Organization gave us complete information in the case. The “Secret Operations Code” was superseded on 2 December 1930 at the beginning of the new Fiscal year, giving them a clean slate so far as security was concerned. The Japanese naval building program was expanded, particularly in cruisers and submarines. And in 1931 Japan began the conquest of Manchuria. Apparently 1930 was “Y-Year” of the Japanese long-range strategic plan.

To the best of my recollection, our report on the 1930 Orange Maneuvers was not disclosed to the Office of Naval Intelligence until 1933 or later. Admiral Pratt felt that he could not trust the Acting Director and put a taboo on the whole office just to play safe.

As a result of our secret participation in the Japanese Maneuvers, as well as our complete success in the solution of Japanese Diplomatic Codes and ciphers, the D.N.C. advised the Secretary of the Navy in a secret memorandum dated 21 January 1931: “The U.S. Navy has at the present moment as complete an ascendency over the Japanese Navy in the matter of radio intelligence as the British Navy had over the German Navy during the World War. This fact has been carefully guarded and it should be known only to officers actually engaged in this work. One suspicion on the part of the Japanese would undo the accomplishments of seven years.” To this was added a pencil note by Commander Kingman: “Not true today 1934 on account of Yardley’s book, H.F.K.”

The first cryptologic flag officer of the Navy and head of the Naval Security Group from 1944 to 1949, RADM Wenger held important positions on the joint staff of the U.S. European Command and the Joint Chiefs of Staff. He helped establish the Armed Forces Security Agency and served as Vice Director of its successor, the National Security Agency.  Prior to his retirement he served as chairman and U.S. member of the Communications Electronic Board, Standing Group, NATO.

By L. F. Safford, Captain, USN