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