Naval Messages Intercepted between 6 September and 4 December 1941
This appendix contains seventy-two selected Japanese naval messages intercepted between September and 4 December 1941 by Navy intercept sites at Hawaii, Guam, and Corregidor; these messages were not decoded and translated until September 1945-May 1946. At the end of the appendix are three diplomatic messages pertaining to the crisis which were translated on 8 and 30 December 1941. The Japanese naval messages are part of a total of 26,581 Japanese dispatches examined by U.S. Navy cryptanalysts.
The Japanese messages were originally discovered in a sanitized but unpublished group of 188 messages contained in a document obtained from the Navy Archives at Crane, Indiana by the then NSA Historian, Mr. Henry Schorreck. Subsequently, some of the messages were located among approximately 2,400 translations given to the National Archives by NSA in 1978-79. Wherever this occurs, the appropriate reference number (SRN) is provided. Under these circumstances, it is not yet possible to verify in what Japanese cryptosystem each message was enciphered, nor have all the messages in the unpublished source been found in those released to the National Archives. (See particularly SRN-115202 to SRN-117840.)
It is interesting to note that the work of decrypting and translating these messages occurred at the same time that the congressional investigation of the attack on Pearl Harbor was being conducted. A review of the material provided witnesses before the congressional committee and to the committee itself by the Navy's Pearl Harbor Liaison Officer, however, indicates that these messages were not made available to the Liaison Office. Ship identifications were taken from Conway's All The World's Fighting Ships, 1922-46 (New York: Mayflower Books, 1980) and organizational relationships from The Imperial Japanese Navy in WW II, prepared in 1952 by U.S. Army, Far East Command, Military History Section.
The reader will note a 27 November 1941 message from Imperial Headquarters to the Striking Force containing the names of two Russian freighters, the Uzbekistan and the Azerbaidjan. The messages announced their presence in the Northern Pacific. Unhindered by restrictions of any kind, they were probably communicating with their owners in the Soviet Union. Their signals would have neatly supplied the basis for Seaman Z's sensational revelations that he had tracked the Japanese Striking Force's radio signals as it steamed toward Pearl Harbor. This episode is outlined in many secondary sources but most recently by John Toland and Edwin Layton in their books, Infamy, Pearl Harbor and its Aftermath and And I Was There, respectively.
To: 2nd Fleet
"A state of complete readiness for battle operations must be achieved by the first part of November ... exert even greater efforts toward achieving maximum fighting strength. ..."
To: All Fleet COS;
All Flt CINCs
"As conditions become more and more critical, each and every ship and unit will aim at being fully prepared for commencing war operations by the first part of November ... completing all personnel changes ordered 3 August ASAP." SRN-115533
Between 4 October and 15 November the 1stAirFlt conducted almost daily drills at fueling at sea. The messages were most revealing in that their addressees actually showed the force structure of the Strike Force and their respective Trains (Tankers).
CdrKagoshima Air Grp
In 1st Air Flt aerial torpedo attack drill #13, which was to be conducted on 21 October against BatDiv1, Akagi and Kaga were each allotted nine torpedoes and "Sooryuu" and "Hiryuu" are each allotted six torpedoes. SRN-117453
From: Staff Combined
To: All Flags
This message concerned the first Combined Fleet Communications drill. It contained the first references to a Striking Force and Advanced Expeditionary Force and mentioned dispatches suitable for X+17, X+30, and X+45 days.
From: Tokyo Comms
This message revised a Navy Call List by adding callsigns for new warships over a year before commissioning: the Yamato (BB) and the Agano (CL).
From: COS Sasebo SND
"Warship Agano launched ... today." SRN-116139
1st Air Flt,
Tokyo DF Control,
This message announced the second Combined Fleet Comm Test and again cited the "Striking Force." Possible leading role for 1stAirFlt in Striking Force. SRN-117089
From: COS1stAir Flt
This message requested that all ships scheduled to be assigned to the (Striking Force?) have all torpedoes adjusted by 18 November. SRN-116684
Experience has shown that in operations the Train frequently preceded the Main Body. Accordingly, Train-related messages were important. This message identified four tankers to be assigned 1stAirFlt and to rendezvous at Sasebo by 10 November.
From: Staff1stAir Fleet
Message arranged torpedo launching exercise for CarDivs1/2/5.
[Three messages to and from 1stAirFlt reinforced idea that CINC1stAirFlt was commander of Strike Force.] "On 30 October this Fleet will pick up from 5-10 (near surface) torpedoes at Sasebo. ... Classes on this torpedo will be held at Kanoya for about five days from the 31st and then (emphasis) will be shifted to firing practice. By working night and day it should be possible to complete 100 (attachments for torpedoes, probably bow or stern planes) by 5 November." SRN-117301
"As the increase in the number of torpedoes handled and the lack of personnel is causing grave delays in torpedo adjusting, please make special arrangements to send to this fleet from Yokosuka Air Group -- about 60 torpedo adjustment personnel to assist in the work of adjusting torpedoes between the end of October and 20 November -- 40 to Kanoya for CarDivs1/2 -- 20 to Ooita Air for CarDiv5. ... Please arrange increase of one torpedo officer to each of the carriers in CarDivs1/2/5." SRN-116323
From: Yokosuka ND
"Send personnel and workers to carry out instructions on Type 91 torpedoes (equipped with stabilizers). ..." SRN-116476
On 27 and 28 October arranged for two tankers to join his fleet by about 10 November -- the Shinkopu Maru and Toohoo Maru. In the meantime these tankers were being equipped for refueling under tow.
Maru or Shinkoku Maru
Info: Kure NavyYrd
Kure Sanda Section
"When installation of gear for refueling undertow and preparations for action have been completed, Kuroshio (KOKU/CHOO) Maru and Shinkoku (KAMI/KUNI) Maru will depart Sasebo and Kure, respectively, on the 13th and proceed to Kagoshima Bay, conducting exercises with carriers en route. Request they load fuel oil for refueling purposes before they depart." SRN-116588
"After completing battle preparations Tooei Maru will obtain about 750 drums of fuel oil (for use of Akagi) and 12,000 kerosene tins of fuel oil (for Hiryu) from Yokosuka ... and rendezvous at Sasebo 10th. ..." SRN-117150
" ... Kinu and Yura will ambush and completely destroy the U.S. enemy." SRN-117001
From: Navy Minister
To: Yokosuka ND
"Have Air Depots 2 and 11 supply live bombs to Akagi, Soryu, Hiryu Shokaku, and Zuikaku to ascertain their capabilities. ..." SRN-117665
A message from the Chief of Naval Technical Bureau, General Affairs Section, to the Yokosuka, Sasebo, Kure, and Maizuru Yards emphasized that work on transport vessels be completed by 20 November.
"In the 3rd Special Drill in ambushing, 54 shipboard bombers will carry out a bombing and strafing attack in sight of Saeki Base from 0815 on the 4th, 0715 on the 5th, and 0815 on the 6th, and about an hour or hour and a half afterward 54 shipboard attack planes will carry out a similar bombing attack." SRN-117665
"CdrDesDiv23 will dispatch Yuuzuki (DD) to Saeki to arrive about 0700 the 6th. Yuuzuki will pick up and take to Kagoshima (4) torpedoes which CarDivs1/2 are to fire against anchored capital ships on the morning in question. ..."
The equipment for refueling under tow at sea included special fenders .9mm in diameter, and their requisite lines for attaching them to the tanker. on this date a message listed 10 Mary vessels, at least five of which were firmly associated with the Striking Force. SRN-117031
In addition to refueling from tankers the Strike Force would be required to carry a deck cargo of oil drums. On carriers, the extra weight of the drums was cause for concern as shown by the following advice to COS 1st Air Fleet from the Chief, Bureau Military Affairs Section: "Regarding the loading of drums of fuel oil on ships of your fleet. ... it will affect the strength of the hull and the ship's performance.
A. Amount to be loaded: Akagi, under 600 tons; Soryu and Hiryu under 400 tons, and an equivalent weight will be removed.
B. In the case of Akagi and Hiryu, load amidships and avoid bow and stern.
C. In the case of Soryu, load evenly over length of ship.
D. We have prepared 1400 tons. ..." SRN-116566
The fact that major combat elements of the Strike Force were to be at sea on 13-14 November was revealed in two messages directing fueling at sea exercises for four Maru vessels with Akagi, DesRon1, CruDiv8, CarDiv2 and CarDiv5 and from CdrDesRon1 directing that the Hiryu and a tanker drill on the 15th off Ariake Bay (extreme southern Japan). SRN-115709, 115784
Maintain wartime radio silence on shortwave commencing 0000 November 11, SRN-117687
"Arrangements have been made to (reequip) four Maru vessels for simultaneous port and starboard refueling by 13 November." SRN-117258
This message assigned anchorages at Saeki Wan (western Inland Sea) to the capital ships and tankers of the Strike Force. SRN-115787
From: COS Combined Flt
Action: NavyTechBur Kure Navy Yrd
"In view of the necessity for completing by 17 November the installation for refueling at sea. ..." SRN-116589
This message suggested that the entire Strike Force did not depart Inland Sea on 10 November: "In view of the scheduled operation of this unit it is desirable to complete loading of antiaircraft ammunition and fuses ... for Abukuma, (CL, DesRon1 Flagship) DesDiv17, DesDiv15, and Akigumo (DD launched 4 November 1941 associated with CarDiv5 by (13 November). ..." SRN-115543
The following message seemed to firmly identify CINC1stAirFlt as Strike Force Cmdr: "Please supply the Striking Force with copies of the Special Area Designator List (used by NGS) from those which have already been (secretly) issued to your headquarters." SRN-115381
From Navy Minister
"The publication Wartime Recognition Signals for Japanese Merchant Shipping will be placed in effect 1 December 1941. ..." SRN-115380
"Flagship was changed to Zuikaku at 0830 on 14th ... 1st Section, Zuikaku and Akigumo; 2d Section Shokaku and Oboro." SRN-115712
To: 7 Marus
Message assigned 5 Maru vessels to CINCS1stAir, 2ndFlt, and 4thFlt. SRN-115785
From: Tokyo Bureau of Mil Prep
Message assigned Akebono Maru to 1st Air Flt.
1stAirFlt (less CarDiv4, CarDiv3),
Tokyo DF Control
Hdg resolved question of who commands and composition of the Striking Force: "Strike Force OPORD#1: Commencing 0000 19 November, 'Battle Control' effective for short wave frequencies and 'Alert Control' for long wave." SRN-115397
Two messages revealed details of designator list and scope of forthcoming fleet operations: "Revision #1 to Navy Call list #9 effective November 15: Striking Force, Submarine Force (Southern Force), Maru Force, Communications Force, Commerce Destruction Force, Advance Expeditionary Force, Supply unit. . .(for each force), Southern Force, Northern Force, South Seas Force, E Force (British Malaya)*, H. Force (Dutch East Indies)*, M Force (Philippines)*, Attached Force, G Occupation Force (Guam)*, AA Occupation Force (Wake)* and AF Destruction Units (Midway)* "(*ca 1942)."
From: Chief 1st Section NGS
[The next seven messages were pivotal in locating the Strike Force.] BB Hiei was 1st section of BatDiv3.) "Suzuki (1776) is being sent to your Hq on board Hiei to report inspection results." SRN-116436
From: Chief 1st Section, NGS
To: COS Ominato Guard District
"Please arrange to have Suzuki (1776) who was sent to the 1stAirFlt on business, picked up at about 23 or 24 November at Hittokapu Wan by -- of your command." (Hittokapu Wan is located in the Kurile Islands at about 45N-147-40E). SRN 116643. See also Prange, At Dawn We Slept, Ch 43, 342-52, for identity of Suzuki and his mission.
From: COS Ominato Guard District
"He (Suzuki) will be taken aboard the Kunajiri (CA)." SRN 116920
From: CINC Comb Flt
To: All Flagships Combined Fleet
"The fourth series of communications tests for the Combined Fleet will be held as follows: (on November 22 and 23). 2. Participating Forces: Combined Fleet (However, the forces presently en route to the Standby Location will not receive test). 3. Principal topic for consideration in this drill: Investigation and study of the communications setup required to effectively handle the situation upon opening up of hostilities. ..." SRN 115678 and Prange, At Dawn We Slept, 332.
"...until 2000, the 20th, Yokosuka Comm Zone. Until 800, the 22nd, Ominato Comm Zone. Thereafter, 1stAirFltFlagship Comm Zone." SRN 117673
"...until 2000 the 20th Yokosuka Comm Zone. From 2000 the 20th until 0800 the 22nd, Ominato Comm Zone. Thereafter, 1stAirFlt flagship Comm Zone." (Ominato is approx 41N-141E). SRN 117666/117674
"I-19 will leave Yokosuka Comm Zone on November 21, and enter Ominato Comm Zone. At 1600 November 22 will enter 1stAirFleet Flagship Comm Zone." SRN 116329/116990
Southern Expeditionary Fleet (Less SubRon/6)
"...At 0000 on 21 November repeat 21 November, carry out Second Phase of preparations for opening hostilities." SRN-115385
"Commencing 20 November, when planes (or plane units) are shifted, maintain precautionary shortwave silence."
From: Hainan Guard District
To: Hainan Force Staff
"Report of leakage of secret information regarding the concentration of our troops on Hainan Island to a foreigner. Commencing 24 November no one will be permitted to leave or enter Hainan Island. ..." SRN-115438
Action: COSCarDivs, Combined Flt
"1. Will complete loading fuel oil (aviation gasoline) and other miscellaneous equipment 21 November. 2. The main generator and other minor repairs will be completed 23 November. 3. Expect to get underway on the 24th and join up during morning of 27 November. 4. Striking Force Secret Operation Order #6 has not been received." SRN-115375
From: Navy Minister
To: All Majcoms Afloat
[Radio calls are normally effective for about six months. The last change was on 1 November. The following message is noteworthy.] "Commence using Call List #10 from 1 December and discontinue using List #9 as of 30 November."
"We are now undergoing overhaul at Yokosuka. Expect to depart November 24 and arrive Sea on November 27. Advise rendezvous point with your unit. Regard fueling at sea ..." (DesDiv7 is escort of CarDiv1, Akagi and Kaga)
Kasuga Maru and Hokaze (DD) CarDiv4 ordered to transport planes from Sasebo to Palau ASAP.
From: Chief, 1st Section, Naval Sec, Imperial Hq
The Japanese had maintained a close interest in the U.S. Marines at Shanghai and Tientsen for several weeks and knew they would be evacuated on the American liners President Madison and President Harrison. This message ordered COS China Area Fleet to report time of departure by urgent dispatch to 2nd and 3rd Fleets, 2nd China Expeditionary Fleet and Bako Guard District. See SRN 116737, 27 November.
"... Since we have assigned all eight patrol boats to the Philippine Force and orders for their use have already been issued ..." SRN-116910
To: All Flagships
"From 26 November, ships of Combined Fleet will observe radio communications procedure as follows:
1. Except in extreme emergency the Main Force and its attached force will cease communicating. ..." SRN-116866
From: Imperial Hq,
COSChina Area Fleet,
All ND COS
"(Plans) for exhaustive conscription of ... and civilians are in hands of Central Authorities. In order to preserve security, however, they will be activated at a future time. ..." SRN-116908
Anticipating casualties the Navy arranged for hospital facilities for the end of December. "Complete all necessary arrangements for the hospitalization of 1,000 patents each at Bako (including Takao), Sama, and Palau. ... Be prepared to supply ten times the annual 'battleship requirements' of medical supplies for dressing of wounds and disinfection by 10 February 1942." SRN-115439
"In view of this force's operations and future we definitely desire to be refueled before arriving at Palau. ..."
To: Striking Force
"Although there are indications of several ships operating in the Aleutians area, the ships in the Northern Pacific appear chiefly to be Russian ships. ... They are Uzbekistan (about 3,000 tons ... 12 knots) and Azerbaidjan (6,114 tons less than 10 knots). Both are westbound (from San Francisco)." SRN-116667
To: All Fleets
To: Striking Force,
"1. Weather report. The low pressure center of 740mm which was near 'N RI 0 Na' today at noon, is advancing at a speed of 45km. Wind speed is over 15m, within 1000km to SW of center and about 26mm near the center. The high pressure center in "RU" area continues to proceed eastward at a speed of 45km. 2. Prince Hiroyasu Fushimi send the following msg to CINC Nagumo: 'I pray for your long and lasting battle fortunes.'" SRN-116668
From: Navy Minister
To: All Majcoms,
CINC All Guard Districts
"From now on all merchant shipping, all Naval Comm units, and Naval Shipping will stand radio guard (Listening watch) as set forth in Articles 12 and 13 of Secret Communication Regulations for Merchant Shipping." SRN-115636
From: Imperial Hq.
To: All Majcoms
"Beginning 1 December 1941, Tokyo Comm Unit will initiate broadcasts on ... 4175kc in order to (maintain) volume of traffic ... afloat, etc., in accordance with principles given in 2nd Communications Analysis of 1941."
Sec, Imperial Hq.
To: All Majcoms,
All Guard Dist,
Tokyo Hydro office
"Commencing this date, in special weather reports sent from (this office) locations will be indicated by Navy Grid Chart -- afloat weather list." SRN-115456
Sec, Imperial Hq
To: Striking Force
"At noon on the 28th a high pressure area of __mm located in 'TSU' and 'HE' sectors moving ESE ... 55kmh. Another high pressure center of about the same pressure in 'U' sector is almost stationary. ..." SRN-115690
"All capital ships, destroyers, submarines of the South Sea Force and the Kukokawa Maru are to maintain battle condition short wave silence, starting 1200 Nov 29." SRN-115435
"The following forces are to be added to the special landing forces for the "U" Occupation Operations. ..." SRN-115396
"At 0200 the 30th, auxiliary gunboat ASO Maru observed three American minesweepers (650 tons) of __ class at point 10 miles on a northeasterly course. In reference to __ #81, it is believed that the Pescadores and Takao areas are being reconnoitered. We are attempting to confirm these movements." SRN-117290
To: Striking Force
"At noon on the 30th, a high pressure area of __mm located in "YU," "RE," "TSU," "HO," "U" blocks with other areas quiet on the whole. ... conditions will continue for about two more days. At 0900 on the 30th there was a five meter west wind in AI (Oahu*) and rain at AF (Midway*)." (*ca 1942) SRN-115460
Area Base Force
"We have received word from Naha customs that the Philippine registered ship KUROBEERUGOO (kana) (44-ton) arrived in Naha on 30 Nov. Seal her radio at once -- delay departure of this ship -- prevent their learning of our activities." SRN-117693
"This ship is proceeding direct to position 30-00N, 154-20E. Expect to arrive that point at 1800 on 3 Dec. Thereafter will proceed eastward along the 30 degree North latitude line at speed of 7 knots." SRN-115398
To: Combined Flt
"This dispatch is Top Secret. This order is effective at 1730 on 2 December. Climb NIITAKAYAMA 1208, repeat 1208." (Climb Mount Niitaka December 8) SRN-115376 (In late 1945, possibly with knowledge in hand that this message was stipulated in Flt OPORDER#1, its meaning is understood by OP-20-G to be, "Attack on 8 December." In the congressional investigation this message was incorrectly reported as sent on 6 December 1941. (Hearings Part 1, 185))
To: All ND CINCS
All GD CINCS
All Fleet CINCS
"Starting 4 December 1941, system #8 of Naval Code D will be used and system #7 discontinued. (List 7 will still be used with some Japanese stations.)" SRN-116741
From: Tokyo (Togo)
[In connection with the CarDiv2 message of 4 November 1941 regarding preparations to fire torpedoes against anchored capital ships, the following message in a naval attaché system was particularly noteworthy. This message was received in Washington on 23 December 1941 and translated by the Army on 30 December 1941. (Connorton, Appendix 1, 194, item 87)] "In view of the present situation the presence in port of warships, airplane carriers, and cruisers is of the utmost importance. Hereafter, advise me whether or not the warships are provided with anti-[torpedo] nets."
To: Combined Flt
"From 0000, Dec 4th change ship frequency system to #1. ..."
From: BurMilPrep, Tokyo
To: NavAttaché, Washington, Mexico
[Only one message was found after 0000 4 December 1941 in the old cipher which could have been read before 8 December.] "Copy being sent by wire to Naval Attaché London. Dispose of the Cipher Machine and all of its rules for use at once."
[Regarding the torpedo net message of 2 December in diplomatic channels the following was translated by the Army on 8 December 1941]: "... in my opinion the battleships do not have torpedo nets. ..."