The first Japanese diplomatic messages of great importance in the present war informed us that Japan and Germany had extended the scope of the “Anti-Comintern Pact” and would declare war on the United States if the latter interfered with the Axis program of conquest in Europe or Eastern Asia.

The next important information was that Germany was planning to attack Russia despite the non-aggression pact between the two countries. Intercepted messages from the Japanese Ambassador in Berlin informed us that Berlin was insisting that Tokyo declare war on England and the United States. To this Tokyo replied that the Japanese Government was adhering to the Pact inspirit as well as in letter; that they could not take any hostile step so long as Russia was free to attack their mainland possessions; and their threatening attitude was neutralizing U.S. and British forces which otherwise, would be available for use against Germany. In the autumn of 1941, after the German attack on Russia, Berlin renewed its demands of Japanese assistance, and Tokyo replied that they would make war, but that they would have to do it in their own way and at their own selected time, and that they could not be rushed into the matter. Tokyo also advised that their menacing attitude in Asia was holding large Russian forces in Siberi, and they considered they were giving as much aid to the Axis as if actually at war.

Early in September, Tokyo sent a message to its Ambassador in Washington instructing him to present a note to the State Department, which (with later “interpretations”) amounted to an ultimatum.  This note demanded, among other things that the United States withdraw its support of the Chiang Kai-skek regime in China and require Chaing to unconditionally surrender to the Japanese, and also demanded immediate withdrawal of the United States from the Philippines and recognition of a Japanese sphere of influence covering Eastern Asia and the Southwest Pacific Ocean.  The ultimatum was to expire the 25th of November 1941.  The Japanese Ambassador (Nomura) toned down the note considerably and omitted the most offensive provisions before presenting it to the State Department on 6 September.  It is possible that a note of another date was toned down rather than this one: Nomura was reprimanded for it, in either event.  Nomura believed that a war with the United States would be suicidal for Japan and on several occasions recommended that Tokyo be more reasonable in its attitude.  From our decryptions, the U.S. Government was well informed as to the real intentions of the Japanese Government.  These messages showed Tokyo’s intentions in the matter, and also explained the reason for sending Kurusu to Washington as a Special Enjoy for the final negotiations immediately preceding the outbreak of war.  The Japanese Government expected to be “appeased.” but the internal situation of Japan was so desperate that a foreign war seemed preferable to the status quo.


Diplomatic negotiations between the United States and Japan dragged on throughout November, finally coming to a stalemate.  At the same time Japan was mobilizing invasion fleets at Hainan (for the conquest of Malaya), at Bako (for the conquest of the Philippines), and at Jaluit (for covering these invasions or a direct attack on Hawaii).  Japan had made no open move and we seemed to be drifting into a war in a slow motion fashion.  However, beginning about 29 November 1941, the real, undercover situation began to change rapidly for the worse, but superficially there was little apparent change. 


On 1 December 1941, we learned that London, Manila, Singapore, and Hong Kong had been ordered, that very day, to destroy their cipher machines. This was our first definite warning that Zero Hour was near, and confirmed our information about Japanese intentions which had been gathered by radio direction finder, traffic analysis, and decryption of Japanese naval message at Pearl Harbor and Corregidor.  On 3 December we learned that the Japanese Embassy, Washington, had been directed the day before to burn all codes except two and destroy one cipher machine immediately, and to burn other secret papers at discretion.  We also received information from the British Government that the Japanese Ambassador in London had just destroyed his code machine.  Information to this general effect was sent to the Command-in-Chief, Asiatic Fleet plus the Commandant 16th Naval District “for action,” and to the Commander-in-Chief Pacific Fleet plus the Commandant 14th Naval District “for information,” on 3 December 1941 in two different messages.  (Secret message ‘COPEK’ #031855 was originated by myself and released by the Assistant Director of Naval Communications (CAPT Jos. R. Redman, USN).  Secret message #031850 was originated by CDR McCollum (I believe) and was released by the Director of Naval Intelligence (RADM T. S. Wilkinson, USN).


The next day the Naval Station Guam was ordered, by OpNav secret dispatch 042017 (originated by myself and released by ADM Ingersoll), to destroy all secret and confidential publication except those essential for current purposes and special intelligence, and to be prepared to destroy instantly all classified matter retained. CINCPAC, as well as CINCAF, was made an information addressee of these message.  This same message was sent to Samoa, but in a different cipher system, that day or the next – I am not sure which.

In addition to being in command of the Navy Radio Intelligence Organization, I was directly responsible for our own codes and ciphers and, therefore, checked over with LT T. A. Smith (Code and Cipher Desk) and the Registered Publication Section to see exactly what should be done to protect our codes and ciphers from capture at outlying stations.  I drafted messages to the Naval Attaches of Tokyo, Bangkok, Shanghai, and Peiping, and to the Marine Detachments at Peiping and Tientsin, directing them to destroy all cryptographic aids except their own personal systems (which they were to destroy at discretion), to report compliance by sending the “Boomerang” in plan language, and to report final destruction of the last cryptographic system and other confidential papers by sending the word “Jabberwock” in plain language.  These messages (Opnav Secret 040340 and #040343) were released by ADM Ingersoll in the late afternoon of 3 December 1941.  [The Commander-in-Chief, Pacific Fleet was not made an information addressee of the above messages].  A similar message was sent to a Yangtze River gunboat (the USS WAKE) via the Commander-in-Chief Asiatic Fleet. “Boomerangs” and “Jabberwocks” came trickling in during the next four days until there was complete accountability. The Naval Station Samoa was given the same message as previously sent to Guam, and Naval Station Dutch Harbor was directed to destroy one cipher system which had been used for secret intelligence work.  Code Room Memorandum 050000 dated 5 December 1941 and Op-20-G Memorandum dated 9 December 1941 verify the above.

On 26 November 1941, the Navy Department translated Tokyo Circular #2354 (dated November 19) advising that a warning that “diplomatic relations where becoming dangerous” would be indicated by adding the following words (repeated five times) to Tokyo’s General Intelligence Broadcasts,” at the beginning and at the end:


HIFAHI         EAST          Japan-U.S. Relations
KITA           NORTH         Japan-U.S.S.R Relations
NISHI          WEST          Japan-England Relations
                                     including N.E.I, Thai, and Malaya

This circular was relayed by the Japanese Embassy (Washington) to Rio de Janeiro, Buenos Aires, Mexico City, and San Francesco.


On November 28th, other Navy Department translated Tokyo Circular #2353 (dated November 19) stating that a warning as to the intentions of the Japanese Government with regard to war against Russia, Great Britain, and the United States would be broadcast in case of emergency by means of a false weather forecast included in the daily “Japanese language broadcast” from Tokyo.  The “code” for these occasion consisted of three expressions:

HIGASHI NO KAZEAME      East Wind, Rain – Japan, United States relation in                     

KITA NO KAZ KUMORI      North Wind, Cloudy – Japan – U.S.S.R relations in

NISHI NO KAZE HARE      West Wind Clear – Japan-England relations in danger

The Navy Department promptly notified the War and State Departments as to Circulars #2353 and #2354.  The British R.I. Unit at Singapore also decrypted and translated these “circular” and forwarded the translations to CINCAF, who passed them on to the Navy Department, CINCPAC, Com 16 and Com 14 in CINCAF  secret message 281430 (November 1941 – COPEK file).  The N.E.I. Army read these same two messages and on December 4 furnished translation to the American Consul General (Mr. Foote) and two American Army officers (Thorpe and Slawson), who in turn forwarded the information to their respective Departments.  Batavia confidential message #220 dated 4 December 1941, on file in the State Department, was forwarded to the Navy Department by the State Department Liaison Officer, Mr. Orme Wilson.

To supplement the above information, Navy Department sent to CINCAF, CINCPAC, COM 16 and COM 14 the new schedule of broadcasts by Tokyo Radio that same day (November 28th).

By L. F. Safford, Captain, USN