OP-20-G
Encyclopedia
OP-20-G or "Office of Chief Of Naval Operations (OPNAV), 20th Division of the Office of Naval Communications, G Section / Communications Security", was the US Navy's signals intelligence and cryptanalysis
group during World War II
. Its mission was to intercept, decrypt, and analyze naval communications from Japanese, German
, and Italian
navies. In addition OP-20-G also copied diplomatic messages of many foreign governments. The majority of the sections effort was directed towards Japan
and included breaking the early Japanese “Blue” book fleet code. This was made possible by intercept and High Frequency Direction Finder (HFDF) sites in the Pacific, Atlantic, and continental U.S., as well as a Japanese telegraphic code school for radio operators in Washington D.C.
named Laurance F. Safford was assigned to expand OP-20-G's domain to radio interception. He worked out of Room 2646, on the top floor of the Navy Department
building in Washington DC.
Japan was of course a prime target for radio
interception and cryptanalysis
, but there was the problem of finding personnel who could speak Japanese
. The Navy had a number of officers
who had served in a diplomatic capacity in Japan and could speak Japanese fluently, but there was a shortage of radiotelegraph operators who could read Japanese Morse code
communications sent in kana
. Fortunately, a number of US Navy and Marine
radiotelegraph operators operating in the Pacific had formed an informal group in 1923 to compare notes on Japanese
kana
transmissions. Four of these men became instructors in the art of reading kana transmissions when the Navy began conducting classes in the subject in 1928.
The classes were conducted by the Room 2646 crew, and the radiotelegraph operators became known as the "On-The-Roof Gang". By June 1940, OP-20-G included 147 officers, enlisted men, and civilians, linked into a network of radio listening posts as far-flung as the Army's.
OP-20-G did some work on Japanese diplomatic codes, but the organization's primary focus was on Japanese military codes. The US Navy first got a handle on Japanese naval codes in 1922, when Navy agents broke into the Japanese consulate in New York
, cracked the safe, took photographs of pages of a Japanese navy codebook, and left, having put everything back as they had found it.
Before the war, the Navy cipher bureau operated out of three main bases:
The US Army Signals Intelligence Service
(SIS) and OP-20-G were badly hobbled by bureaucracy. Part of the problem was that they had unsurprisingly become rivals, competing with each other to provide their intelligence data, codenamed "MAGIC
", to high officials. Both organizations came out looking foolish and obnoxious, and word came down that the two groups were to cooperate. That was easier said than done, and rivalries between the two cryptanalysis
teams would remain a problem for a long time. The best that SIS and OP-20-G were able to do was come to an agreement in 1940 to provide MAGIC on alternating days, and try to draw up some vague guidelines for which team handled what traffic. Complicating matters was that the Coast Guard
, the FBI
, and even the FCC
also had radio-intercept operations.
The result was that much of the MAGIC was wasted. There was no efficient process for assessing and organizing the intelligence, or getting it to its proper end users. This was a dangerous problem as the time was rapidly approaching when that data would be a matter of life and death.
on Bainbridge Island, Washington
, picked up a radio message being sent by the Japanese
government to the Japanese embassy in Washington DC. It was the last in a series of 14 messages that had been sent over the previous 18 hours.
The messages were decrypted by a PURPLE analogue machine at OP-20-G and passed to the SIS for translation from Japanese, early on the morning of December 7. Army Colonel Rufus S. Bratton
and Navy Lieutenant Commander Alvin Kramer independently inspected the decrypts.
They both became alarmed. The decrypts instructed the Japanese ambassador to Washington to inform the US Secretary of State, Cordell Hull
, at 1:00 PM Washington time that negotiations between the US and Japan
were ended. The embassy was then to destroy their cipher
machines. This sounded like war, and although the message said nothing about any specific military action, Kramer also realized that the sun would be rising over the expanses of the central and western Pacific by that time. The two men both tried to get in touch with Army Chief of Staff General George C. Marshall.
After some agonizing delays, Marshall got the decrypts and methodically examined them. He realized their importance and sent a warning to field commanders, including Major General Walter Short
, the Army commander in Hawaii. However, Marshall was reluctant to use the telephone because he knew that telephone scramblers weren't very secure and sent it by less direct channels. Due to various constraints and bumblings, Short got the message many hours after the Japanese bombs had smashed the US Navy's fleet at anchor in Pearl Harbor
.
, the possibility of an invasion of Hawaii, and the increasing demand for intelligence, OP-20-G undertook two courses of action:
Cryptanalysis
Cryptanalysis is the study of methods for obtaining the meaning of encrypted information, without access to the secret information that is normally required to do so. Typically, this involves knowing how the system works and finding a secret key...
group during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. Its mission was to intercept, decrypt, and analyze naval communications from Japanese, German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, and Italian
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
navies. In addition OP-20-G also copied diplomatic messages of many foreign governments. The majority of the sections effort was directed towards Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and included breaking the early Japanese “Blue” book fleet code. This was made possible by intercept and High Frequency Direction Finder (HFDF) sites in the Pacific, Atlantic, and continental U.S., as well as a Japanese telegraphic code school for radio operators in Washington D.C.
History
The Code and Signal Section was formally made a part of the Division of Naval Communications (DNC), as Op-20-G, on July 1, 1922. In January 1924, a 34-year-old US Navy lieutenantLieutenant
A lieutenant is a junior commissioned officer in many nations' armed forces. Typically, the rank of lieutenant in naval usage, while still a junior officer rank, is senior to the army rank...
named Laurance F. Safford was assigned to expand OP-20-G's domain to radio interception. He worked out of Room 2646, on the top floor of the Navy Department
United States Department of the Navy
The Department of the Navy of the United States of America was established by an Act of Congress on 30 April 1798, to provide a government organizational structure to the United States Navy and, from 1834 onwards, for the United States Marine Corps, and when directed by the President, of the...
building in Washington DC.
Japan was of course a prime target for radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
interception and cryptanalysis
Cryptanalysis
Cryptanalysis is the study of methods for obtaining the meaning of encrypted information, without access to the secret information that is normally required to do so. Typically, this involves knowing how the system works and finding a secret key...
, but there was the problem of finding personnel who could speak Japanese
Japanese language
is a language spoken by over 130 million people in Japan and in Japanese emigrant communities. It is a member of the Japonic language family, which has a number of proposed relationships with other languages, none of which has gained wide acceptance among historical linguists .Japanese is an...
. The Navy had a number of officers
Officer (armed forces)
An officer is a member of an armed force or uniformed service who holds a position of authority. Commissioned officers derive authority directly from a sovereign power and, as such, hold a commission charging them with the duties and responsibilities of a specific office or position...
who had served in a diplomatic capacity in Japan and could speak Japanese fluently, but there was a shortage of radiotelegraph operators who could read Japanese Morse code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
communications sent in kana
Kana
Kana are the syllabic Japanese scripts, as opposed to the logographic Chinese characters known in Japan as kanji and the Roman alphabet known as rōmaji...
. Fortunately, a number of US Navy and Marine
United States Marine Corps
The United States Marine Corps is a branch of the United States Armed Forces responsible for providing power projection from the sea, using the mobility of the United States Navy to deliver combined-arms task forces rapidly. It is one of seven uniformed services of the United States...
radiotelegraph operators operating in the Pacific had formed an informal group in 1923 to compare notes on Japanese
Japanese language
is a language spoken by over 130 million people in Japan and in Japanese emigrant communities. It is a member of the Japonic language family, which has a number of proposed relationships with other languages, none of which has gained wide acceptance among historical linguists .Japanese is an...
kana
Kana
Kana are the syllabic Japanese scripts, as opposed to the logographic Chinese characters known in Japan as kanji and the Roman alphabet known as rōmaji...
transmissions. Four of these men became instructors in the art of reading kana transmissions when the Navy began conducting classes in the subject in 1928.
The classes were conducted by the Room 2646 crew, and the radiotelegraph operators became known as the "On-The-Roof Gang". By June 1940, OP-20-G included 147 officers, enlisted men, and civilians, linked into a network of radio listening posts as far-flung as the Army's.
OP-20-G did some work on Japanese diplomatic codes, but the organization's primary focus was on Japanese military codes. The US Navy first got a handle on Japanese naval codes in 1922, when Navy agents broke into the Japanese consulate in New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
, cracked the safe, took photographs of pages of a Japanese navy codebook, and left, having put everything back as they had found it.
Before the war, the Navy cipher bureau operated out of three main bases:
- headquarters in Washington DC
- Station HypoStation HYPOStation HYPO, also known as Fleet Radio Unit Pacific was the United States Navy signals monitoring and cryptographic intelligence unit in Hawaii during World War II. It was one of two major Allied signals intelligence units, called Fleet Radio Units in the Pacific theaters, along with FRUMEL in...
, a section at Pearl HarborPearl HarborPearl Harbor, known to Hawaiians as Puuloa, is a lagoon harbor on the island of Oahu, Hawaii, west of Honolulu. Much of the harbor and surrounding lands is a United States Navy deep-water naval base. It is also the headquarters of the U.S. Pacific Fleet...
in Hawaii - Station CastStation CASTStation CAST was the United States Navy signals monitoring and cryptographic intelligence fleet radio unit at Cavite Navy Yard in the Philippines, until Cavite was captured by the Japanese forces in 1942, during World War II. It was an important part of the Allied intelligence effort, addressing...
, a section in the fortified caves of the island of CorregidorCorregidorCorregidor Island, locally called Isla ng Corregidor, is a lofty island located at the entrance of Manila Bay in southwestern part of Luzon Island in the Philippines. Due to this location, Corregidor was fortified with several coastal artillery and ammunition magazines to defend the entrance of...
, in the PhilippinesPhilippinesThe Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
. The codebreakers were backed up by a far-flung network of listening and radio direction finding stations.
The US Army Signals Intelligence Service
Signals Intelligence Service
The Signals Intelligence Service was the United States Army codebreaking division, headquartered at Arlington Hall. It was a part of the Signal Corps so secret that outside the office of the Chief Signal officer, it did not officially exist. William Friedman began the division with three "junior...
(SIS) and OP-20-G were badly hobbled by bureaucracy. Part of the problem was that they had unsurprisingly become rivals, competing with each other to provide their intelligence data, codenamed "MAGIC
Magic (cryptography)
Magic was an Allied cryptanalysis project during World War II. It involved the United States Army's Signals Intelligence Section and the United States Navy's Communication Special Unit. -Codebreaking:...
", to high officials. Both organizations came out looking foolish and obnoxious, and word came down that the two groups were to cooperate. That was easier said than done, and rivalries between the two cryptanalysis
Cryptanalysis
Cryptanalysis is the study of methods for obtaining the meaning of encrypted information, without access to the secret information that is normally required to do so. Typically, this involves knowing how the system works and finding a secret key...
teams would remain a problem for a long time. The best that SIS and OP-20-G were able to do was come to an agreement in 1940 to provide MAGIC on alternating days, and try to draw up some vague guidelines for which team handled what traffic. Complicating matters was that the Coast Guard
United States Coast Guard
The United States Coast Guard is a branch of the United States Armed Forces and one of the seven U.S. uniformed services. The Coast Guard is a maritime, military, multi-mission service unique among the military branches for having a maritime law enforcement mission and a federal regulatory agency...
, the FBI
Federal Bureau of Investigation
The Federal Bureau of Investigation is an agency of the United States Department of Justice that serves as both a federal criminal investigative body and an internal intelligence agency . The FBI has investigative jurisdiction over violations of more than 200 categories of federal crime...
, and even the FCC
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
also had radio-intercept operations.
The result was that much of the MAGIC was wasted. There was no efficient process for assessing and organizing the intelligence, or getting it to its proper end users. This was a dangerous problem as the time was rapidly approaching when that data would be a matter of life and death.
Attack on Pearl Harbor
In the dark hours of the morning of 7 December 1941, the U.S. Navy communications intercept station at Fort WardFort Ward (Washington)
Fort Ward is a former United States Army coastal artillery fort, and later, a Navy installation located on the southwest side of Bainbridge Island, Washington, along Rich Passage.-Early:...
on Bainbridge Island, Washington
Bainbridge Island, Washington
Bainbridge Island is a city in Kitsap County, Washington, United States, and the name of the island in Puget Sound on which the city is situated...
, picked up a radio message being sent by the Japanese
Empire of Japan
The Empire of Japan is the name of the state of Japan that existed from the Meiji Restoration on 3 January 1868 to the enactment of the post-World War II Constitution of...
government to the Japanese embassy in Washington DC. It was the last in a series of 14 messages that had been sent over the previous 18 hours.
The messages were decrypted by a PURPLE analogue machine at OP-20-G and passed to the SIS for translation from Japanese, early on the morning of December 7. Army Colonel Rufus S. Bratton
Rufus S. Bratton
Colonel Rufus S. Bratton was Chief of the Far Eastern Section of the Intelligence Branch of the Military Intelligence Division in the War Department in December 1941, when the United States entered World War II....
and Navy Lieutenant Commander Alvin Kramer independently inspected the decrypts.
They both became alarmed. The decrypts instructed the Japanese ambassador to Washington to inform the US Secretary of State, Cordell Hull
Cordell Hull
Cordell Hull was an American politician from the U.S. state of Tennessee. He is best known as the longest-serving Secretary of State, holding the position for 11 years in the administration of President Franklin Delano Roosevelt during much of World War II...
, at 1:00 PM Washington time that negotiations between the US and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
were ended. The embassy was then to destroy their cipher
Cipher
In cryptography, a cipher is an algorithm for performing encryption or decryption — a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. In non-technical usage, a “cipher” is the same thing as a “code”; however, the concepts...
machines. This sounded like war, and although the message said nothing about any specific military action, Kramer also realized that the sun would be rising over the expanses of the central and western Pacific by that time. The two men both tried to get in touch with Army Chief of Staff General George C. Marshall.
After some agonizing delays, Marshall got the decrypts and methodically examined them. He realized their importance and sent a warning to field commanders, including Major General Walter Short
Walter Short
Walter Campbell Short was a Major General in the United States Army and the U.S. military Commander responsible for the defense of U.S. military installations in Hawaii at the time of the Japanese attack on Pearl Harbor on December 7, 1941.-Early life:He was born in 1880 in Fillmore, Illinois...
, the Army commander in Hawaii. However, Marshall was reluctant to use the telephone because he knew that telephone scramblers weren't very secure and sent it by less direct channels. Due to various constraints and bumblings, Short got the message many hours after the Japanese bombs had smashed the US Navy's fleet at anchor in Pearl Harbor
Pearl Harbor
Pearl Harbor, known to Hawaiians as Puuloa, is a lagoon harbor on the island of Oahu, Hawaii, west of Honolulu. Much of the harbor and surrounding lands is a United States Navy deep-water naval base. It is also the headquarters of the U.S. Pacific Fleet...
.
After Pearl Harbor
As Japanese advances in the PhilippinesBattle of the Philippines (1941-42)
The Philippines Campaign or the Battle of the Philippines was the invasion of the Philippines by Japan in 1941–1942 and the defense of the islands by Filipino and United States forces....
, the possibility of an invasion of Hawaii, and the increasing demand for intelligence, OP-20-G undertook two courses of action:
- the staff and services of CAST were progressively transferred to a newly-formed US-AustraliaAustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n-British station, FRUMELFRUMELFleet Radio Unit, Melbourne was a United States-Australian-British signals intelligence unit, based in Melbourne, Australia during World War II. It was one of two major Allied signals intelligence units, called Fleet Radio Units, in the Pacific theatres, the other being FRUPAC , in Hawaii...
in MelbourneMelbourneMelbourne is the capital and most populous city in the state of Victoria, and the second most populous city in Australia. The Melbourne City Centre is the hub of the greater metropolitan area and the Census statistical division—of which "Melbourne" is the common name. As of June 2009, the greater...
, Australia.
- another signals intelligence center, known as NEGAT was formed in Washington, using elements of OP-20-G headquarters.
Section Evolution
- (July 1922-March 1935) Code and Signal Section (Op-20-G), Division of Naval Communications (DNC), OCNO (July 1922-March 1935).
- (March 1935-March 1939) Communications Security Group (Op-20-G), DNC, OCNO
- (March 1939-September 1939) Radio Intelligence Section (Op-20-G), DNC, OCNO
- (October 1939-February 1942) Communications Security Section (Op-20-G), DNC, OCNO
- (February 1942-October 1942) Radio Intelligence Section (Op-20-G), DNC, OCNO
- (October 1942-July 1946) Communications Intelligence Organization (Op-20-G), DNC, OCNO
- July 10, 1946 All Naval communications intelligence elements were collectively designated "Communications Supplementary Activities" of the 20th Division of the Office of Naval Communications, Section 2, (Op-20-2)