The Orange secret maneuvers of 1930 were analyzed through decryption of the ciphers employed. Here (1933) an effort has been made to obtain the same and by attack from an entirely different angle.

In time of war it is to be expected that codes and ciphers normally used by the enemy will be changed at once. Even if the new cryptographic system can be successfully solved, the task of breaking them down will require days, if not weeks, to accomplish. Until this is done the flow of intelligence will be stopped and stopped during the critical period of the commencement of hostilities when the plan of campaign is being laid and information concerning the enemy is essential to success.

Codes and ciphers may be changed readily upon the outbreak of war. However, the communications system or method of handling traffic, which has taken years to evolve and perfect cannot be so easily superseded. It is upon this hypothesis that the foregoing study has been made. That the communications system alone can be a source of valuable intelligence, this analysis, it is believed, has definitely demonstrated. The intelligence to be expected from this source is chiefly of a strategic nature. If properly and skillfully exploited, it can provide information essential to a correct estimate of the situation. This being true, radio intelligence activities are vitally important in time of peace, especially where strained relations exist.

In addition to the above conclusions, Wenger made a number of recommendations to CINCAF which were forwarded to Washington for action. Some of them had been heard previously, but now there was ample basis for the Navy to take heed. Recommendations 3 and 6 cited below were the genesis of radio traffic analysis training in the Navy. Recommendation number 1 was the basis for establishing a COMINT unit at Corregidor, and number 2 provided the impetus for the development of effective DF in the Navy.

  1. Locate at least one intercept unit in the ultimate defense area so that it can function without interruption upon the outbreak of the war.
  2. Equip all stations with suitable long range direction finding apparatus and the best obtainable receivers.
  3. Train all operators in the proper coordination of DF and frequency measurement with traffic interception for the deduction of intelligence by the methods in the report.
  4. Provide sufficient intercept operators to coordinate the three phases of intercept work.
  5. Establish a decrypting center in connection with, or in the vicinity of the intercept station in the ultimate defense area.
  6. Provide at least two cryptanalysts, one translator, and two clerks for the analysis of intercepted material.
  7. Conduct intercept activities on the Asiatic station in time of peace not only with the idea of studying the Orange communications system, but with the more important mission of preventing surprise attack.
  8. Continue the policy of preserving the utmost secrecy concerning intercept activities in order to protect the source of supply of radio intercept.

 The Maneuvers of 1934 and 1935: More Challenges

 There were still more challenges to be met and overcome during the years directly before Pearl Harbor. The Grand Fleet Maneuvers of 1934 posed two major problems for the U.S. Navy: the employment of stringent security measures by the Japanese and the proximity of the maneuvers to the Japanese home territory. The 1934 maneuvers were not as ambitious in scope as those of the previous year, and the Japanese realized the need for additional security to deny the U.S. Navy information concerning the activities of their fleet.

The Japanese emphasized three areas to improve their communications security from 1933: regulation of power and frequency, shifting frequencies, and changing callsigns and addresses. In 1934, the Imperial Fleet employed many more frequencies in the same ranges and decreased their power whenever a main shore station cleared traffic directly to the fleet. The use of the HF range was sharply curtailed, and the fleet tactical units maneuvered near to shore rather than in open waters where they could be observed by the U.S. Navy.

During the exercise, U.S. Navy COMINT units intercepted the Japanese sending a message on one frequency and shifting to another frequency in the middle of a transmission. The U.S. operators believed the Japanese were employing some automatic method of doing this since no frequency shift alert was given to the receiving station.

Moreover, the Japanese did not assign permanent callsigns and addresses to stations as in previous years. In addition, they no longer assigned similar secret calls and addresses to similar vessels. Callsigns and addresses were apparently a combination of different types, and they were changed at frequent intervals. Each vessel and command was assigned one secret call to be effective for one month or less. Flagships used separate callsigns for each frequency and addresses were changed simultaneously with the callsigns. Secret call signs were apparently assigned at random.

Although only a meager amount of traffic was monitored during the exercise, the U.S.Navy intercept and analytic effort was able to inform CINCAF of the immediate location of the main Japanese naval forces. Regardless of this success, the intercept war had clearly been balanced through the Japanese denial practices in 1934. They realized the potential for signals intelligence and took action to deny the U.S. Navy combat information. In addition to the increased communications security, the Japanese employed effective DF and were able to regularly locate the USS Augusta, the CINCAF flagship.

In 1935, the success of the U.S. Navy effort was not any better than in 1934. The Japanese employed broadcasts to alert their fleet and new secret callsign and address systems were introduced. Encipherment increased and the Japanese, according to a human intelligence (HUMINT) report, introduced a new radio transmitting at 120 mHz.

 Source: NSA

(a) Featured image is Makalapa – FRUPAC Section GW – Raw Traffic into FRUPAC from Guam, etc through Wahiawa.