Not only did traffic analysis aide cryptanalysts in their attack on encrypted text messages, but in a wartime situation it provided valuable order of battle, force disposition and movement intelligence information to the U.S. surface and submarine attack forces!
At the Battle of Midway, the cryptanalytic feat of establishing in advance the probable date of the impending attack has been to obscure the fact that many precious days in advance of that feat, U.S. aircraft carriers were moved to the general Midway area not on the basis of information extracted from decrypted messages, but rather on the basis of intelligence derived from traffic analysis. Because callsign associations related the Japanese base of Kwajalien to that activity, it appeared that the force was preparing for a strike in the Eastern Pacific. Traffic analysts were able to correctly identify every ship in the Japanese force with the exception of one small transport.
Traffic analysts who worked the problem have often been asked why we weren’t able to provide such information before Pearl Harbor. That was pretty well explained in an issue of the Naval Institute Proceedings after the war. A young Japanese Naval officer explained that radio was not used to promulgate the operational plans for that attack, since all the forces involved were in home waters. All orders were hand carried from Headquarters to the Fleet Commands by officer couriers. Further, the Japanese Fleet operators maintained strict radio silence after departure from Japan en route to Hawaii.
The traffic analysts from Station “C” were able to be evacuated from Corregidor and set up a decryption center in Melbourne, Australia, which was then named Fleet Radio Unit Melbourne (FRUMEL). Those at Pearl Harbor were soon augmented by many OTRG operators, many operators from General Service, and officers and men who entered the navy after the start of hostilities. This activity as well as the intercept station at Wahiawa became known as Fleet Radio Unit Pacific (FRUPAC), a name which has been assumed by a network of amateur radio operators who had been active duty members of the Naval Security Group. The decryption center was moved to its own building at Makalapa, only a few steps from the headquarters of Commander In Chief Pacific Fleet (CINCPAC) and a short distance from Pearl Harbor. One of those who volunteered for navy service and was assigned to FRUPAC in the traffic analysis group was LTJG John Paul Stevens, USNR, and former U.S. Supreme Court Justice.
A small contingent of traffic analysts was sent to Guam in 1944, shortly after the Marines had secured the island. Message format and callsign recoveries were the principal source of intelligence. During the Okinawa campaign when the Japanese began using Kamikaze pilots to attack our fleet, the departure of the planes were reported by radio to interested commands. The format of those message made it possible for the traffic analysts and cryptanalysts provide CINCPAC, who had since moved his headquarters to Guam, an additional thirty minute warning of the oncoming attacks.
Source: NCVA/ Carl Jensen
Edited By Mario Vulcano
16 February 2019 at 19:35
Very interesting series of articles, Mario! Well written. I’ve long questioned the story about HYPO and other crypto units not knowing what “AF” referred to. I’m pretty sure that the entire story that Jasper Holmes concocted the idea to instruct Midway to send a message in the clear stating that their fresh water condenser was broken down, is a canard. (I’m avoiding going into any details about Japanese naval codes in the book version of Time to Reexamine Pearl Harbor. I’m not a cryptanalyst or electronic warfare specialist as you well know. Right now I’m working on a fairly brief follow-up essay to what I sent you last year titled, “Associations.” I’m writing this for you, Mario. I’m touching on items that indicate just how much we knew prior to 7 Dec. 1941 that was kept covered-up by our own people throughout the eight investigations into Pearl Harbor. Admiral Aquilino asked last December if I really believed that Admiral Kimmel and General Short had the same intelligence Washington had. I said something to the effect, “I sure do” and added that “I’ll bet my life on this.”
Two of the officers working in HYPO were actually attached to Kimmel’s CinCPac staff. On 5 December 1941 a new crypto system went into effect for the sole use of the CNO and CinCPac. (I have a copy of the CinCPac dissemination list together with a handwritten note on it about this new system.) Then Captain E.M. Zacharias was asked by John W. Murphy of the JCC in early 1946, “…Do you know of any books, any pamphlets, or any address [speech] anywhere in your lifetime where you ever heard that [HEK’s remarks about destruction of Japanese codes] until this case?” Zach replied, “There is nothing of that nature on which he could base it, unless he had information that was specially available to him.” I believe Zacharias knew precisely what he was speaking about.
The first general counsel to the JCC, William D. Mitchell, made an interesting comment to the JCC (PHA01, p. 221) in which he states the following during the testimony of Rear Admiral T.B. Inglis: “I don’t believe we quite understand what these gentlemen have been asked to do. In the outline of the case and the nature of the proof which was furnished to the committee on the 2nd of November  is found first an analysis of the attack from the American point of view and second the attack from the Jap point of view and it contains this statement: `The Jap plan will be reconstructed from captured plans and statements made by Jap prisoners obtained AFTER the attack.`” Based on this restriction, Admiral Inglis stated that the Combined Fleet’s Climb Mount Niitaka message was sent on 5 Dec. 1941 (U.S. date). Hypo’s copy of the intercept gives its TOI as: 12022100 and a frequency of 4155. Then Captain E.T. Layton told the JCC that he was of the opinion the IJN never sent such a dispatch. The first time I ever saw a copy of that intercept was in the appendix to “And I Was There”: Pearl Harbor and Midway – Breaking the Secrets.
Pearl Harbor happened over seventy-seven years ago. As of today, no book or article I’ve read contains an accurate explanation regarding the level of intelligence that was available in 1941 to the senior Hawaiian commanders. The many authors who have written about it either: (1) Relied too heavily on the 25 conclusions given in the JCC’s majority report from 1946; (2) Did little or no research outside of the JCC’s report and the reading of other peoples books and articles; (3) Did not understand what they were researching and writing about; (4) Probably had little or no respect for the men and women who serve in the Armed Forces of the United States of America.
I have absolutely no doubt in my mind that our senior military leadership allowed Pearl Harbor to happen. We took a number of important steps which reduced the number of casualties we had to accept. False claims to the contrary, I have not found a single example of incompetence in any of our senior military personnel in the period leading up to 7 December 1941. Admiral Stark told Admiral R.K. Turner’s biographer, VADM G.C. Dyer: “Probably nobody in Washington had a better understanding of the Japanese situation than Kelly did.” While I’m quoting this from memory, I interpret this to mean that Turner had not only a superior knowledge of Japanese plans and intentions but also knew what American war plans (based on Rainbow 3 and Rainbow 5) called for.
I’ve read all 39-volumes of the Pearl Harbor Attack Hearings. All of it, Mario. If my conclusions are believed to be harmful to our armed forces in general, or to the Navy in particular, I’ll “archive” my findings and my research and keep my mouth shut about what I’ve done and why I’ve done it.
I never had—and never will have—any desire to harm or discredit our armed forces. I have no desire to write anything that could discredit officers and enlisted personnel who served their country honorably. I believe that many people who never served in our armed forces will be critical of the fact that we accepted the loss of X-number of personnel in what has long been referred to as “a sneak attack” or “a sneak raid” made on select units of the U.S. Pacific Fleet.
Great article on TA, Mario. I enjoy reading the Station HYPO blog, even though much of what appears on there is over my head. Suffice it to say, as a researcher whose dedicated the past 35 years of his life to the subject of Pearl Harbor, I have the utmost faith and respect in the Navy’s electronic warfare people. Thank you all for your service!
(Not proof read, so I can get back to work on the “Associations” essay to send to you, Mario.)
Andy McKane, from Springville, Utah soon to reside full time on Molokai, Hawaii.