World War II:
The importance of COMINT is fully recognized


The rapid increases in personnel experienced by the Signals Intelligence Section (SIS) soon brought about an overcrowding of the space allotted to it in the Munitions Building. Additional space was sought, first in the Munitions Building, then in the Pentagon, and finally in nearby Virginia. In June 1942 the Army purchased Arlington Hall Station which was to serve as headquarters for the SIS and the 2nd Signal Service Company . The Army also acquired Vint Hill Farms in 1942 and a COMINT intercept station (referred to as the Eastern Primary Monitoring Station) was activated at Vint Hill along with the Signals Interception and Deciphering training school . The Signal Corps began constituting a few signal intercept units designated as Signal Service units but it isn't until the U.S. involvement in World War II that large numbers of these units are constituted. On 14 April 1942 the 2nd Signal Service Company was reorganized as the 2nd Signal Service Battalion.

Army Chief of Staff General of the Army Dwight D. Eisenhower, accompanied by Assistant Chief of Staff, G-2 MAJ. Gen. Hoyt S. Vandenberg, visit Arlington Hall Station early in 1946. In the center is Army Security Agency Chief Brig. Gen. W. Preston Corderman. Next to him are two noted Army cryptologists, Col. Frank Bullock and Mr. William Friedman. Communications intelligence provided by Arlington Hall was the Armys most important single source of information during World War II. (U.S. Army Photo)

By the time the U.S. entered World War II, Friedman and his small organization (SIS ) had not only invented new electromechanical cipher machines of unparalleled security for U.S. communications, but had succeeded in breaking the PURPLE cipher system that carried most secret Japanese diplomatic messages.

Another pioneer in the Signal Corps, COL William Blair, director of the Signal Corps laboratories at Fort Monmouth patented the first Army radar in 1937. Mass production of two types of radar sets began before the U.S. even entered the war. Along with the Signal Corps new tactical FM radio, also developed in the 1930's, radar was the most important communications development of World War II. Radar would be used extensively on aircraft and ships during the war.

The British began using airborne radar prior to U.S. entry into the war. The Germans, who could not at first understand the British night-fighters ability to find German bombers at night, were mislead by a rumor that John Cunningham, the Royal Air Force's most successful night fighter pilot, had developed phenomenal night sight by eating large quantities of carrots.

The surprise attack on Pearl Harbor by the Japanese on December 7, 1941, brought America into the war and immediately focused attention on intelligence shortfalls within the U.S. Entering the war, the Army's intelligence organization consisted of two elements - the Signals Intelligence Service (SIS) ,which would be redesignated the Army Signal Security Agency (SSA) in July of 1943 and was based at Arlington Hall Station, and at the Army Staff level, the G2/Military Intelligence Division (MID) located in Washington D.C. .

CLICK HERE TO READ "Too Late for Pearl Harbor" a report on Washington's knowledge (or lack of) of Japan's intentions to strike Pearl Harbor

In the aftermath of Pearl Harbor, there was a general reorganization of the War Department General Staff. All operating functions of G-2 were placed under a separate Military Intelligence Service (MIS) (it will control all field intelligence units), and the Military Intelligence Service created a tightly compartmented Special Branch to evaluate (and later, disseminate) intelligence product derived from SIGINT. The Special Branch was organized from a section of the Far Eastern Branch of the MIS. It's primary mission was to exploit and protect "MAGIC" intercept - Japanese diplomatic code traffic. COL Carter W. Clarke was designated the branch Chief with COL Alfred McCormark serving as his deputy chief. By June 1944, the staff of the Special Branch had reached a strength of 382, larger than all other intelligence production elements within the MIS put together. Several factors led to the decision to discontinue the Special Branch at that time and its functions were absorbed by the MIS.

As the war went on, communications intelligence became the single most important intelligence source, and the Special Branch rapidly expanded. Finally, in the summer of 1944, MIS was reorganized, and SIGINT made available to additional intelligence analysts. The MIS provided intelligence analysis to the U.S. and allied commands by providing intelligence staffs at a tactical level (down to Battalion). These staffs were usually comprised of small teams (detachments) of HUMINT and PHOINT specialists. On the tactical SIGINT side, intercept was done by Signal Corps units responsible to the SSA . These units were designated as Radio Intelligence Companies or Signal Service Companies and concentrated on exploitation of enemy low and medium level encryption systems. In December 1944 the Military Intelligence Service (MIS) assumed operational control of the Army Signal Security Agency (SSA), leaving the Signal Corps to carry on the administrative functions. Under the SSA/MIS , intelligence elements were assigned directly to operating forces at Army and Corps level in the field.


Army SIGINT operations in the PACIFIC began in 1936 when Lt Mark Rhodes of the Signal Intelligence Service (SIS) established the 10th Signal Service Detachment in Manila. This small detachment intercepted Japanese press broadcasts, diplomatic traffic, some military messages and any Kana code it could hear. The intercept was then passed to the SIS for training at its school.

In response to Japan's aggression in the Pacific, in July 1941 General MacArthur sets up the Army Forces Far-East command in Manila. Soon afterwards Det 6, 2nd Signal Service Company arrives. The detachment is headed by Major Joe Sherr with Lt Howard W. Brown as it operations officer. There are 6 Sergeants, 3 Corporals and 6 Privates in the detachment. It is not clear if the 10th Signal Service Det integrated with the 2nd Signal Service unit or continued operations on its own.

On December 8 1941 the Japanese begin bombing the Philippines. On December 22 1941 the Japanese invasion force landed at Lingayen, 100 miles west of Manila.

The 2nd Signal Service Company personnel were evacuated on Christmas Eve and its men moved to Corregidor with the rest of MacArthur's staff. Radio intelligence operations cease and most the units members are reassigned. Those that remain are allowed to open a small intercept station in Corregidors Malinta Tunnel.

During this time MacArthur's forces were performing a double-retrograde maneuver, moving from Luzon to Bataan Peninsula and then to the island of Corregidor. Many of the units never made it further than Bataan. About 2,300 military and civilians would escape from Bataan to Corregidor. The scores of thousands remaining became the victims of the infamous Bataan Death March to the O'Donnell and Cabanatuan prisoner of war camps, otherwise known as "hell camps.

On 17 March 1942 MacArthur leaves the Philippines for Australia. MAJ Sherr departs with General MacArthur because he was a master of cryptanalysis and deemed important to the war effort. Lt Brown evacuates on 14 April and is flown to Australia where he joins MacArthur's SIGINT operation there. Some of the other members of the Signal Service unit departed in the various evacuations conducted prior to the final fall of the island but not all managed to escape.


General Douglas MacArthur escaped from Corregidor in the Philippines in a PT boat to Mindanao and flew to Australia from Del Monte on a B-17 Flying Fortress. He made his way to Melbourne, arriving there on 22 March 1942. One of his first decisions when he arrived in Melbourne was to expand the SIGINT operations that already existed in Australia. The United States Navy crypto group that had been evacuated from Manila in early January 1942 was operating in Melbourne. They were responsible for channeling all SIGINT information to US Navy headquarters in Washington. MacArthur was not happy to depend on the Navy's discretion to handle his SIGINT requirements. He had experienced problems with such an arrangement when he was in Manilla.

MacArthur released orders for a joint American-Australian SIGINT organization called Central Bureau to be established under the command of Major General S. B. Akin with its headquarters based in Melbourne. General MacArthur advised Washington of his decision in a despatch on 1 April 1942. He described the role of the group as "the interception and cryptanalyzing of Japanese intelligence".

The existing experienced RAAF intercept Kana operators at Townsville were integrated into the new Central Bureau. The RAAF at the time had a number of Kana operators being trained and were about to train a further 13 WAAAF personnel. "Kata Kana" was a form of Japanese written and spoken language.

Major General Akin bought the American interceptors who had survived the Malinta Tunnel at Corregidor back to Australia by submarine. They were used to assist the Australian Wireless Group units. A group of cryptographic, cryptanalytic and translator personnel from the Japanese section of the Washington Signal Intelligence Service were also moved to Australia. More Australians were also recruited to Central Bureau after its initial establishment.

Initially Central Bureau was made up of 50% American, 25% Australian Army and 25% RAAF personnel.

On 25 April 1942 the small RAAF Unit operating in two back to back houses at 21 Sycamore Street and 24 French Street in the suburb of Pimlico in Townsville was given its new name of No. 1 Wireless Unit . The newly named Unit comprised 7 RAAF, 1 AMF and 4 United States Army personnel in No. 1 Wireless Unit at Townsville . This RAAF Unit had started earlier in March 1942 as a small intercept station located in the initial two houses at Pimlico under Wing Commander Booth.

By 6 July 1942 the intercept operator numbers at Central Bureau had increased from six to twenty nine. On 20 July 1942, General MacArthur moved his Headquarters to Brisbane. Central Bureau immediately relocated to Brisbane, establishing its headquarters in a huge house at 21 Henry Street, high on a hill in the suburb of Ascot, not far from the new American airfield at Eagle Farm .

Four US Signal Radio Intelligence Companies, with detachments and D/F units, served in the Australia. They made a massive contribution to the overall effort, particularly because of their huge intercept capacity which, month by month, usually exceeded that of the Australian Army Wireless Sections and RAAF Wireless Units combined. First in the field was 126 SRIC, a section of which, under Lieutenant W.R. Menear, had arrived in Melbourne as early as April, 1942, and had become operational first at Mt. Macedon, then at Townsville and finally in Brisbane where it merged with the main company when the latter arrived from USA in March, 1943.

Many fixed SIGINT stations came on-line during World War II. Here are a few:


To train soldiers to conduct intelligence operations, the MID organized the Intelligence Training Center at Fort Ritchie Maryland. Intercepters, interrogators, order of battle specialists and photo interpreters were trained. The school was closed as part of the demobilization after the war.

On 1 November 1941 a linguistic "boot camp" was started as a secret school at Persidio of San Francisco's Crissy Field. In May of 1942 the school was moved to Camp Savage (Graphic courtesy of the Japanese American Veterans Association) and later to Fort Snelling, both in Minnesota. In June of 1946 the school made its final move to Monterey California where it operates today.

The Signal School began teaching courses on intercepting Japanese Kana code in September of 1933.



The PURPLE Cipher Machine

Working under conditions of the tightest secrecy, the SSA exploit the elaborate codes used by the Japanese Army. General MacArthur's operations officer thought the exploits of the SSA shortened the war in the Pacific by two years. Other Allied successes were attributed to the advantages gained by cracking the German ENIGMA and Japanese PURPLE cipher systems. Tactical advantages were also gained by Crypt analysts working at operational and tactical levels for the allies. In North Africa, the 129th Signal Company (Radio Intelligence) discovered the Nazi's were withdrawing from Kasserine Pass. Later in North Africa the 128th gave advance warning of several attacks. In Italy, radio reconnaissance units provided "outstanding" intelligence support to VI Corps. Crypt analysts working for General Omar Bradley's 12th Army Group, the 849th Signal Intelligence Service (SIS), read a German message at Normandy which allowed Bradley to respond to a strong counterattack against one of his vulnerable positions. Later, the 849th SIS working in the Ardennes was able to decipher German message traffic disclosing the movement of armored divisions in the region of the Ardennes Forest. Another SIS unit working for General Patton's 3rd Army, deciphered a German message that contributed to the 3rd Army inflicting heavy losses on the German 5th Parachute Division at Bastogne. Crypt analysts continued to provide valuable support until the conclusion of the War.

The Army was not blind to the value of intelligence in World War II, in fact they counted signals intelligence as second in importance only to photographic intelligence, but this fact was hidden because of a tight veil of secrecy kept over intelligence operations, even after the war ended. The war also saw the advancement of a new form of warfare - electronic combat. ELINT (Electronic Intelligence) was born during World War II as radar emerged as an intelligence target. Responsibility for the collection and processing of ELINT was controlled by the Signal Corps

World War II also fostered the first formalized cooperation between U.S. and British intelligence activities. Of all the areas of intelligence collaboration, it was in the area of signals intelligence that the most important and vital cooperation took place. Cooperation began in the spring of 1941 when the U.S. delivered a model of the Japanese PURPLE machine to British codebreakers at Bletchley Park. In return the British gave the U.S. an assortment of advanced crypto logical equipment, including the Marconi-Adcock high speed frequency direction finder.

The U.S. and British agencies also exchanged personnel and decided on a division of labor, with the British responsible for Tokyo-London traffic and the U.S. responsible for Tokyo-Washington traffic. Any useful result of these codebreaking efforts was shared among the two countries.

Because both British and U.S. commanders in the field required up to date intelligence, it was necessary to broaden the original exchange (which covered the interception of diplomatic messages only) to include intercepted military traffic. Britains production of such intelligence was labeled ULTRA. Although ULTRA information was made available to U.S. commanders, the exact nature of it's acquisition was initially obscured. It wasn't until April 1943 that the British revealed to U.S. MI officials that they could break the ciphers produced by the German ENIGMA machine used for much of German military communications.

Test out the ENIGMA
machine yourself

Britain was not the only allied country that the U.S. cooperated with. U.S. - Canadian cooperation began in October 1941 when the Canadians offered the FCC free access to the product of its monitoring activities. In return, the U.S. provided Canada with technical direction-finding data. Canadian DF stations subsequently made significant contributions to the Allied North Atlantic SIGINT network.

Increased cooperation also existed between U.S., Australian and New Zealand intelligence agencies. It was with respect to Japan, however, that SIGINT cooperation among allied nations reached its highest level. Monitoring stations in Canada, particularly the major one at Halifax, gathered large quantities of coded Japanese transmissions. In April 1942, a combined Allied signals intelligence agency for the Pacific, The Central Bureau of the Allied Intelligence Bureau, was activated in Melbourne with a U.S. Chief and an Australian Deputy Chief.

Additional Information - Communication types in use during World War II