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DEPARTMENT OF THE NAVY -- NAVAL HISTORICAL CENTER
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COMINT [Communications Intelligence] Contributions [to] Submarine Warfare in WW II

SRH [Special Research History] 235
17 June 1947
VADM [Vice Admiral] C. [Charles] A. Lockwood USN
COMSUBPAC [Commander Submarine Forces, Pacific]

25, D.C.
17 June 1947

From: Vice Admiral C. A. Lockwood, USN.
To: Chief of Naval Communications.

Subject: Communication Intelligence against the Japanese in World War II.

Enclosure: (A) Statement as to value of subject activity.

1. I am enclosing herewith a statement as to the value of communication intelligence against the Japanese in World War II.

2. I feel that this is a very modest outline and that there are undoubtedly a very great number of incidents and examples which time and memory have obliterated. However, I hope that there will be no thought of curtailing the operations of this activity, or of eliminating research and training in peacetime of a facility which must of necessity be immediately available on the approach of war.

C. A. Lockwood

Contribution of Communication Intelligence to the Success of Submarine Operations Against the Japanese in World War II.

The contribution to the defeat of Japan in World War II by United States submarines is a matter of record. More than two-thirds of the entire Japanese merchant marine and numerous warships, including some of every category, were sunk. These sinkings resulted, by mid-1944, in isolation of Japan from her overseas sources of raw materials and petroleum, with far reaching effects on the capability of her war industry to produce and her armed forces to operate. Her outlaying bases were weakened by lack of reinforcements and supplies and fell victim to our air, surface and amphibious assaults; heavy bombers moved in to the captured bases and decimated and demoralized the Japanese to the point where they were forced to accept unconditional surrender. These effects of submarine operations have been substantiated, both from Japanese and Allied official records, and for the most part have been made public in detail, but nothing has been told about the manner in which such outstanding results were achieved by such a relatively small submarine organization.

As Commander of the Submarine Force, U.S. Pacific Fleet, from February, 1943, through the end of hostilities, I can vouch for the very important part which Communication Intelligence played in the success of the submarine campaign. Through intercept, cryptanalysis and translation of Japanese messages, Communication Intelligence supplied the Submarine Force with a continuous flow of information on Japanese naval and merchant shipping, convoy routing and composition, damage sustained from submarine attacks, anti-submarine measures employed or to be employed, effectiveness of our torpedoes, and a wealth of other pertinent intelligence.

The Submarine Force Operations Officer was designated the Combat Intelligence Officer. He was given access to all of the Communication Intelligence files and through him information was furnished to the Force Commander and thence to the individual submarines concerned. A private telephone was installed between SubPac operations office and the combat intelligence center of JICPOA [Joint Intelligence Center, Pacific Ocean Areas] so that information on convoy routing could be supplied with a minimum of delay. Special internal codes, carried only by submarines, were used for relaying this type of information, so that our own surface ships, though they might be able to decipher the submarine messages, were unable to determine the type of information being supplied. When ComSubPac moved his operational headquarters to Guam a special cryptographic channel was authorized by OpNav [Office of the Chief of Naval Operations] to supply this information direct from JICPOA at Pearl Harbor.

The information furnished made possible the assignment of submarines not only to the most profitable patrol areas but also to specific locations at particular times where contacts were made with convoys of known composition and importance, and frequently with enemy course and speed known exactly. Combatant units of the Japanese Fleet were similarly located on many occasions. During periods, which fortunately were brief, when enemy code changes temporarily cut off the supply of Communication Intelligence, its absence was keenly felt. The curve of enemy contacts and of consequent sinkings almost exactly paralleled the curve of volume of Communication Intelligence available. There were many periods when every available submarine on patrol in the Pacific Ocean Area was busy on information supplied by Communication Intelligence. The vast reaches of the Pacific Ocean could not otherwise have been covered so thoroughly unless a far greater number of submarines had been available. In early 1945 it was learned from a Japanese prisoner-of-war that it was a common saying in Singapore that you could walk from that port to Japan on American periscopes. This feeling among the Japanese was undoubtedly created, not by the great number of submarines on patrol, but rather by the fact, thanks to Communication Intelligence, the submarines were always at the same place as Japanese ships.

Regulations required that messages containing Communication Intelligence be destroyed, and as a consequence, no record of the many successes due to this intelligence can ever be compiled. However, some of the more notable achievements come immediately to mind:

Severe damage to carrier Hitaka (or Hiyo) by Trigger in June, 1943, which put her out of commission for almost a year.

Sinking of aircraft transport Mogamigawa by Pogy in August, 1943.

Sinking of escort carrier Chuyo by Sailfish in December, 1943.

Sinking of submarine I-42 by Tunny in March, 1944.

Decimation of large Saipan-bound convoy by Pintado and Shark II just prior to our landings on that island.

Sinking of submarine I-29 by Sawfish in July, 1944.

Sinking of submarine I-41 by Sea Devil in September, 1944.

Sinking of escort carrier Jinyo by Spadefish in November, 1944.

Sinking of carrier Unryu by Redfish in December, 1944.

Severe damage to carrier Hayataka (or Junyo) by Redfish and/or Sea Devil in December, 1944, which put her out of commission for remainder of war.

Sinking of submarines RO-115, RO-112 and RO-113 by Batfish within four days in February, 1945.

Sinking of submarine RO-56 off Wake Island by Sea Owl in April, 1945.

Sinking of light cruiser Isuzu by Charr in April, 1945.

Contact and trailing of Yamato task force by Threadfin and Hackleback in April, 1945 which resulted in sinkings the following day by carrier air forces of the battleship Yamato, the cruiser Yahabi, and destroyers Hamakaze, Isokaze, Asashino and Kasumi.

The above are but a few of the many successes against the Japanese Navy that can be directly attributed to Communication Intelligence. The sinkings of Japanese merchant ships resulting from Communication Intelligence ran into hundreds of ships and probably amounted to fifty percent of the total of all merchantmen sunk by submarines.

In addition to the direct results there were equally as important indirect results which must be credited to the same source of information. For example: From an analysis of Communication Intelligence extending over a period of many months it was determined that our magnetic torpedo exploders were not functioning properly, and steps were taken to correct the defects. Then again, information concerning enemy minefields was so complete that defensive minefields laid down by the enemy served our purpose rather than his. Not only were our submarines able to avoid the areas of danger, but Japanese ships, being required to avoid them as well, were forced into relatively narrow traffic lanes, making it easier for the submarines to locate and attack them. It is impossible to estimate the number of our submarines which were saved and the number of Japanese ships which were lost because of the accurate information about enemy minefields supplied by Communication Intelligence. Also, information concerning names of ships sunk, nature of cargo and number of troops lost was of inestimable value is assessing damage sustained by the enemy and gauging his capabilities.

Without Communication Intelligence submarine operations would unquestionably have been far more difficult and costly because of the vast areas which had to be covered and the attainment of the ultimate objectives would have been greatly delayed.

/s/ C. A. Lockwood


Source: Cryptologic Documents Collection, Navy Department Library. Also available at the National Archives and Records Administration, College Park, Maryland, in Record Group (RG) 457, Records of the National Security Agency.


Note: The opinions expressed in this document are those of the author and do not necessarily represent the views of the Naval Historical Center.


Definition: Communications Intelligence (COMINT) is the technical and intelligence information derived from foreign communications by other than the intended recipients. COMINT is produced by the collection and processing of foreign communications passed by electromagnetic means and by the processing of foreign encrypted communications. COMINT does not include the intercept and processing of press, propaganda and other public broadcasts except for processing encrypted or hidden meaning passages in such broadcasts.


07 March 2006