Pearl Harbor Advance-knowledge Conspiracy Theory - Detection of Japanese Transmissions

Detection of Japanese Transmissions

There are claims that as the Kido Butai (the Striking Force), steamed toward Hawaii, radio signals were detected that alerted U.S. intelligence to the imminent attack. For instance, the Matson liner SS Lurline, heading from San Francisco to Hawaii on its regular route, is said to have heard and plotted via "relative bearings" unusual radio traffic, in a telegraphic code very different from International Morse which persisted for several days, and came from signal source(s) moving in an easterly direction, not shore stations - presumably the approaching Japanese fleet. There are numerous Morse Code standards including those for Japanese, Korean, Arabic, Hebrew, Russian, and Greek. To the experienced radio operator, each has a unique and identifiable pattern. For example, kana, International Morse, and "Continental" Morse all have a specific rhythmic sound to the "dit" and "dah" combinations. This is how Lurline's radiomen, Leslie Grogan, a U.S. Navy reserve officer in naval communications, and with decades of maritime service in the Pacific identified the mooted signal source as Japanese and not, say, Russian.

There are several problems with this analysis. Surviving officers from the Japanese ships state there was no radio traffic to have been overheard by anyone: their radio operators had been left in Japan to send fake traffic, and all radio transmitters aboard the ships (even those in the airplanes) were physically disabled to prevent any inadvertent or unauthorized broadcast.

The Kido Butai was constantly receiving intelligence and diplomatic updates. Regardless of whether Kido Butai broke radio silence and transmitted, there was a great deal of radio traffic picked up by its antennas. In that time period, it was not unknown for a radio antenna to reflect the energy of an incoming signal back to the ionosphere, where ionospheric skip could result in its reception hundreds or even thousands of miles away. Since the Kido Butai contained a large number of possible reflectors, it thus is conceivable the task force did not break radio silence but was detected anyway.

Such detection would not have helped the Americans track the Japanese fleet. A radio direction finder (DF or RDF) from that time period reported compass direction without reference to distance. (Moreover, it was common for the receiving stations to generate erroneous reciprocal bearings.) To locate the source, a plotter needed two such detections taken from two separate stations to triangulate and find the target. If the target was moving, the detections must be close to one another in time. To plot the task force's course with certainty, at least four such detections must have been made in proper time-pairs, and the information analyzed in light of further information received by other means. This complex set of requirements did not occur; if the Kido Butai was detected, it was not tracked.

According to a 1942 Japanese after action report, "In order to keep strict radio silence, steps such as taking off fuses in the circuit, and holding and sealing the keys were taken. During the operation, the strict radio silence was perfectly carried out... The Kido Butai used the radio instruments for the first time on the day of the attack since they had been fixed at the base approximately twenty days before and proved they worked well. Paper flaps had been inserted between key points of some transmitters on board Akagi to keep the strictest radio silence..." Commander Genda, who helped plan the attack, stated, "We kept absolute Radio Silence." For two weeks before the attack, the ships of Kido Butai used flag and light signals (semaphore and blinker), which were sufficient since task force members remained in line of sight. Kazuiyoshi Koichi, the Communications Officer for Hiei, dismantled vital transmitter parts and kept them in a box that he used as a pillow to prevent Hiei from making any radio transmissions until the attack commenced. Lieutenant Commander Chuichi Yoshoka, communications officer of the flagship, Akagi, said he did not recall any ship sending a radio message before the attack. Furthermore, Captain Kijiro, in charge of the Kido Butai's three screening submarines, stated nothing of interest happened on the way to Hawaii. Vice Admiral Ryūnosuke Kusaka stated, "It is needless to say that the strictest radio silence was ordered to be maintained in every ship of the Task Force. To keep radio silence was easy to say, but not so easy to maintain." There is nothing in the Japanese logs or after action report indicating that radio silence was broken until after the attack. Kusaka worried about this when it was briefly broken on the way home.

The appendix to the war-initiating operational order is also often debated. The message of 25 November 1941 from CinC Combined Fleet (Yamamoto) to All Flagships stated, "Ships of the Combined Fleet will observe radio communications procedure as follows: 1. Except in extreme emergency the Main Force and its attached force will cease communicating. 2. Other forces are at the discretion of their respective commanders. 3. Supply ships, repair ships, hospital ships, etc., will report directly to parties concerned." Furthermore, "In accordance with this Imperial Operational Order, the CinC of the Combined Fleet issued his operational order ... The Task Force then drew up its own operational order, which was given for the first time to the whole force at Hitokappu Bay... In paragraph four of the appendix to that document, the especially secret Strike Force was specifically directed to 'maintain strict radio silence from the time of their departure from the Inland Sea. Their communications will be handled entirely on the general broadcast communications net.'" In addition, Genda recalled, in a 1947 interview, Kido Butai's communications officer issuing this order, with the task force to rely (as might be expected) on flag and blinker.

The original records of Lurline surrendered to Lt. Cmdr. George W. Pease, 14th Naval District in Honolulu, have disappeared. Neither Lurline's log, nor the reports to the Navy or Coast Guard by Grogan in Hawaii can be found. Thus no contemporaneously written evidence of what was recorded aboard Lurline is now available. Grogan commented on a signal source "moving" eastward in the North Pacific over several days as shown via "relative bearings" which then "bunched up" and stopped moving. However, the directions given by Grogan in a recreation of the logbook for the Matson Line were 18 and 44° off from known strike force positions and instead pointed towards Japan. According to author Jacobsen, Japanese commercial shipping vessels are the likely source. A recently discovered missing report by Grogan, dated 10 December 1941 and titled "Record for Posterity", also does not support claims of Kido Butai broadcasting.

The Japanese practiced radio deception. Susumu Ishiguru, intelligence and communications officer for Carrier Division Two, stated, "Every day false communications emanated from Kyushu at the same time and same wavelength as during the training period." Because of this, Commander Joseph Rochefort of Hawaii Signals Intelligence concluded that the First Air Fleet remained in home waters for routine training. The ships left their own regular wireless operators to carry on "routine" radio traffic. Captain Sadatoshi Tomioka stated, "The main force in the Inland Sea and the land-based air units carried out deceptive communications to indicate the carriers were training in the Kyushu area." The main Japanese naval bases (Yokosuka, Kure, and Sasebo) all engaged in considerable radio deception. Analysis of the bearings from Navy DF stations account for claimed breaks of radio silence, and when plotted, the bearings point to the Japanese naval bases, not where those ships actually were.

Rochefort, with Huckins and Williams, states there were no dummy messages used at any time throughout 1941 and no effort by the Japanese to use serious deception. When asked after the attack just how he knew where Akagi was, Rochefort (who commanded at the time) said he recognized her "same ham-fisted" radio operators. (The Japanese contend that radio operators were left behind as part of the deception operation.) The critical DF-tracked radio transmissions show bearings that could have not come from the strike force. Emissions monitored from, or 's report Akagi was off Okinawa on 8 December 1941, are examples, though some transmissions continue to be debated. The contention that "low-powered" radio (such as VHF or what the U.S. Navy called TBS, or talk between ships), might have been used, and detected, is contradicted as impossible due to the tremendous distances involved and when contact was lost, it was routinely presumed it was because low-powered radio and land line were being used. Freedom of Information Act (FOIA) requests for specific RDF reports remain wanting. "A more critical analysis of the source documentation shows that not one single radio direction finder bearing, much less any locating "fix," was obtained on any Kido Butai unit or command during its transit from Saeki Bay, Kyushu to Hitokappu Bay and thence on to Hawaii. By removing this fallacious lynchpin propping up such claims of Kido Butai radio transmissions, the attendant suspected conspiracy tumbles down like a house of cards."

One suggested example of a Kido Butai transmission is the November 30, 1941 COMSUM14 report in which Rochefort mentioned a "tactical" circuit heard calling "marus". (a term often used for commercial vessels or non-combat units). Further, the perspective of U.S. naval intelligence at the time was, "... The significance of the term, 'tactical circuit' is that the vessel itself, that is Akagi, was using its own radio to call up the other vessels directly rather than work them through shore stations via the broadcast method which was the common practice in Japanese communications. The working of the Akagi with the Marus, indicated that she was making arrangements for fuel or some administrative function, since a carrier would rarely address a maru."

Also, from a U.S. Navy radiomen on duty at STATION AE (STATION Able Easy, Sitka, Alaska) at the time of Pearl Harbor, Elmer H. Frantz, states, "It is inconceivable to me that a force represented by the Kido Butai with 33 ships involved of all different types ... and no radio communications, communication black out on orders - I just don't believe it."

One story from author Constantine Fitzgibbon claimed that a letter received from V. F. W. Cavendish-Bentinck stated Britain's JIC met and discussed at length the impending Japanese attack on Pearl Harbor. From a Joint Intelligence Sub-Committee session of 5 December 1941 it was stated "We knew that they changed course. I remember presiding over a J.I.C. meeting and being told that a Japanese fleet was sailing in the direction of Hawaii, asking 'Have we informed our transatlantic brethren?' and receiving an affirmative reply." However the author was incorrect. There was no session on the 5th of Dec nor was Pearl Harbor discussed when they did meet on the 3rd.