Station HYPO
Encyclopedia
Station HYPO, also known as Fleet Radio Unit Pacific (FRUPAC) 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 Unit
s in the Pacific theaters
, along with FRUMEL
in Melbourne
, Australia
. The station took its initial name from the phonetic code at the time for "H", as in "Hawaii". The precise importance and role of HYPO has been the subject of considerable controversy, reflecting internal tensions amongst US Navy cryptographic stations.
HYPO was under the control of the OP-20-G
Naval Intelligence section in Washington. It was located, prior to the attack on Pearl Harbor
of December 7, 1941, and for sometime afterwards, in the basement of the Old Administration Building at Pearl Harbor
. Later on, a new building was constructed for the station, though it had been reorganized and renamed by then.
were largely those related to Japan
. An early decision by OP-20-G in Washington divided responsibilities for them among CAST
at Cavite
and then Corregidor
, in the Philippines
, HYPO in Hawaii, and OP-20-G itself in Washington. Other Navy crypto stations, including Guam
, Puget Sound
, Bainbridge Island were tasked and staffed for signals interception and traffic analysis
.
The US Army's SIS
broke into the highest level Japanese diplomatic cypher (called PURPLE
by the US) well before the attack on Pearl Harbor. PURPLE produced little of military value, as the Japanese Foreign Ministry was thought by the ultra-nationalists
to be unreliable. Furthermore, decrypts from PURPLE, eventually called MAGIC
, were poorly distributed and used in Washington. SIS was able to build several PURPLE machine equivalents. One was sent to CAST, but as HYPO's assigned responsibility did not include PURPLE traffic, no PURPLE machine was ever sent there. The absence of such a machine on site in Hawaii has long been seen by conspiracy theorists
as a reason for US unpreparedness in Hawaii, and/or to be evidence of a conspiracy by high level officials to deprive Pearl Harbor of intelligence known to Washington. However, no hard evidence for any such conspiracy exists.
, the United Kingdom
and Netherlands
to share the effort, worked with crypto groups based at Melbourne
, Hong Kong
and Batavia
. Prior to the attack on Pearl Harbor, the amount of available IJN traffic was low, and little progress had been made on the most important Japanese Navy system, called JN-25
by U.S. analysts. JN-25 was used by the IJN for high level operations: movement and planning commands, for instance. It was a superencrypted code
, eventually a two-book system, and was about the state-of-the-art at the time. Cryptanalytic progress was slow. Most references cite about 10% of messages partially (or sometimes completely) decrypted prior to 1 Dec 41, at which time a new edition of the system went into effect sending the cryptanalysts back to the beginning.
After the attack on Pearl Harbor, there was considerably more JN-25 traffic as the Japanese Navy operational tempo increased and geographically expanded, which helped progress against it. Hong Kong's contribution stopped until the crypto station there could be relocated (to Ceylon and eventually Kenya
), but HYPO and the Dutch at Batavia, in conjunction with CAST and OP-20-G made steady progress. HYPO in particular made significant contributions. Its people, including its commander, Joseph Rochefort
, thought a forthcoming Japanese attack early in 1942 was intended for the central Pacific, while opinion at OP-20-G, backed by CAST, favored the North Pacific, perhaps in the Aleutians.
In early 1942, in response to the Japanese advances in the Philippines
(which threatened CAST), the possibility of an invasion of Hawaii, and the increasing demand for intelligence, another signals intelligence center, known as NEGAT was formed in Washington, using elements of OP-20-G. In the words of NSA
historian Frederick D. Parker:
One of HYPO's personnel was responsible for the ruse which identified a call sign used in the Japanese traffic related to a new offensive operation being planned. This involved a false claim of a fresh water shortage on Midway, broadcast in clear, which succeeded in evoking an encrypted Japanese response, noting that AF was reporting water troubles. Since AF was the apparent focus of the upcoming operation, it was clear that Midway would be the primary target.
As mid-1942 approached, HYPO was under high pressure, and there are tales of 36-hour stints, of Rochefort working in his bathrobe and appearing for briefings late and disheveled besides. This effort climaxed in the last week of May with the decryption of enough JN-25 traffic to understand the Japanese attack plan at Midway in some, but not complete detail. This allowed Admiral Nimitz to gamble on the ambush which resulted in the Battle of Midway
, the loss of four Japanese carriers and many naval aviators, and what is generally agreed to have been the turning point of the Pacific War.
After having commandeered a girls' school in Washington (the Army took over one too), Naval Intelligence expanded greatly, as did OP-20-G, and HYPO became a smaller proportion of the total Navy signals intelligence effort in the Pacific.
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
signals monitoring and cryptographic
Cryptography
Cryptography is the practice and study of techniques for secure communication in the presence of third parties...
intelligence unit in Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
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...
. It was one of two major Allied
Allies of World War II
The Allies of World War II were the countries that opposed the Axis powers during the Second World War . Former Axis states contributing to the Allied victory are not considered Allied states...
signals intelligence units, called Fleet Radio Unit
Fleet Radio Unit
Fleet Radio Units were the major centers for Allied cryptological and signals intelligence during the Pacific Campaign of World War II. Initially two FRUs were established in the Pacific, one at Pearl Harbor, Hawaii, called Station HYPO or FRUPAC , and the other, called Station CAST or Belconnen,...
s in the Pacific theaters
Pacific War
The Pacific War, also sometimes called the Asia-Pacific War refers broadly to the parts of World War II that took place in the Pacific Ocean, its islands, and in East Asia, then called the Far East...
, along with FRUMEL
FRUMEL
Fleet 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 Melbourne
Melbourne
Melbourne 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
Australia
Australia , 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...
. The station took its initial name from the phonetic code at the time for "H", as in "Hawaii". The precise importance and role of HYPO has been the subject of considerable controversy, reflecting internal tensions amongst US Navy cryptographic stations.
HYPO was under the control of the OP-20-G
OP-20-G
OP-20-G or "Office of Chief Of Naval Operations , 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...
Naval Intelligence section in Washington. It was located, prior to the attack on Pearl Harbor
Attack on Pearl Harbor
The attack on Pearl Harbor was a surprise military strike conducted by the Imperial Japanese Navy against the United States naval base at Pearl Harbor, Hawaii, on the morning of December 7, 1941...
of December 7, 1941, and for sometime afterwards, in the basement of the Old Administration Building at 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...
. Later on, a new building was constructed for the station, though it had been reorganized and renamed by then.
Background
Cryptanalytic problems facing the United States in the Pacific prior to World War IIWorld 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...
were largely those related to 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...
. An early decision by OP-20-G in Washington divided responsibilities for them among CAST
Station CAST
Station 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...
at Cavite
Cavite
Cavite is a province of the Philippines located on the southern shores of Manila Bay in the CALABARZON region in Luzon, just 30 kilometers south of Manila. Cavite is surrounded by Laguna to the east, Metro Manila to the northeast, and Batangas to the south...
and then Corregidor
Corregidor
Corregidor 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 Philippines
Philippines
The 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...
, HYPO in Hawaii, and OP-20-G itself in Washington. Other Navy crypto stations, including Guam
Guam
Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...
, Puget Sound
Puget Sound
Puget Sound is a sound in the U.S. state of Washington. It is a complex estuarine system of interconnected marine waterways and basins, with one major and one minor connection to the Strait of Juan de Fuca and the Pacific Ocean — Admiralty Inlet being the major connection and...
, Bainbridge Island were tasked and staffed for signals interception and traffic analysis
Traffic analysis
Traffic analysis is the process of intercepting and examining messages in order to deduce information from patterns in communication. It can be performed even when the messages are encrypted and cannot be decrypted. In general, the greater the number of messages observed, or even intercepted and...
.
The US Army's SIS
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...
broke into the highest level Japanese diplomatic cypher (called PURPLE
PURPLE
In the history of cryptography, 97-shiki ōbun inji-ki or Angōki Taipu-B , codenamed Purple by the United States, was a diplomatic cryptographic machine used by the Japanese Foreign Office just before and during World War II...
by the US) well before the attack on Pearl Harbor. PURPLE produced little of military value, as the Japanese Foreign Ministry was thought by the ultra-nationalists
Japanese nationalism
encompasses a broad range of ideas and sentiments harbored by the Japanese people over the last two centuries regarding their native country, its cultural nature, political form and historical destiny...
to be unreliable. Furthermore, decrypts from PURPLE, eventually called 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:...
, were poorly distributed and used in Washington. SIS was able to build several PURPLE machine equivalents. One was sent to CAST, but as HYPO's assigned responsibility did not include PURPLE traffic, no PURPLE machine was ever sent there. The absence of such a machine on site in Hawaii has long been seen by conspiracy theorists
Pearl Harbor advance-knowledge debate
The Pearl Harbor advance-knowledge conspiracy theory is the idea that the American officials had advance knowledge of Japan's December 7, 1941 attack on Pearl Harbor...
as a reason for US unpreparedness in Hawaii, and/or to be evidence of a conspiracy by high level officials to deprive Pearl Harbor of intelligence known to Washington. However, no hard evidence for any such conspiracy exists.
Japanese naval signals in 1941 & early 1942
HYPO was assigned responsibility for work on Japanese Navy systems, and after an agreement with AustraliaAustralia
Australia , 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...
, the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
and Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
to share the effort, worked with crypto groups based at Melbourne
Melbourne
Melbourne 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...
, Hong Kong
Hong Kong
Hong Kong is one of two Special Administrative Regions of the People's Republic of China , the other being Macau. A city-state situated on China's south coast and enclosed by the Pearl River Delta and South China Sea, it is renowned for its expansive skyline and deep natural harbour...
and Batavia
Jakarta
Jakarta is the capital and largest city of Indonesia. Officially known as the Special Capital Territory of Jakarta, it is located on the northwest coast of Java, has an area of , and a population of 9,580,000. Jakarta is the country's economic, cultural and political centre...
. Prior to the attack on Pearl Harbor, the amount of available IJN traffic was low, and little progress had been made on the most important Japanese Navy system, called JN-25
JN-25
The vulnerability of Japanese naval codes and ciphers was crucial to the conduct of World War II, and had an important influence on foreign relations between Japan and the west in the years leading up to the war as well...
by U.S. analysts. JN-25 was used by the IJN for high level operations: movement and planning commands, for instance. It was a superencrypted code
Code (cryptography)
In cryptography, a code is a method used to transform a message into an obscured form, preventing those who do not possess special information, or key, required to apply the transform from understanding what is actually transmitted. The usual method is to use a codebook with a list of common...
, eventually a two-book system, and was about the state-of-the-art at the time. Cryptanalytic progress was slow. Most references cite about 10% of messages partially (or sometimes completely) decrypted prior to 1 Dec 41, at which time a new edition of the system went into effect sending the cryptanalysts back to the beginning.
Kenya
Kenya , officially known as the Republic of Kenya, is a country in East Africa that lies on the equator, with the Indian Ocean to its south-east...
), but HYPO and the Dutch at Batavia, in conjunction with CAST and OP-20-G made steady progress. HYPO in particular made significant contributions. Its people, including its commander, Joseph Rochefort
Joseph Rochefort
Joseph John Rochefort was an American Naval officer and cryptanalyst. His contributions and those of his team were pivotal to victory in the Pacific War....
, thought a forthcoming Japanese attack early in 1942 was intended for the central Pacific, while opinion at OP-20-G, backed by CAST, favored the North Pacific, perhaps in the Aleutians.
In early 1942, in response to the Japanese advances in the Philippines
Battle 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....
(which threatened CAST), the possibility of an invasion of Hawaii, and the increasing demand for intelligence, another signals intelligence center, known as NEGAT was formed in Washington, using elements of OP-20-G. In the words of NSA
National Security Agency
The National Security Agency/Central Security Service is a cryptologic intelligence agency of the United States Department of Defense responsible for the collection and analysis of foreign communications and foreign signals intelligence, as well as protecting U.S...
historian Frederick D. Parker:
- By the middle of March 1942, two viable naval radio intelligence centers existed in the Pacific: one in Melbourne, Australia [FRUMEL], and one, HYPO, in Pearl Harbor, Hawaii... The center on Corregidor (CAST) was no longer affiliated with a fleet command, and its collection and processing capabilities were rapidly disintegrating as a result of evacuations of personnel to Australia and destruction of its facilities by bombing and gunfire.
One of HYPO's personnel was responsible for the ruse which identified a call sign used in the Japanese traffic related to a new offensive operation being planned. This involved a false claim of a fresh water shortage on Midway, broadcast in clear, which succeeded in evoking an encrypted Japanese response, noting that AF was reporting water troubles. Since AF was the apparent focus of the upcoming operation, it was clear that Midway would be the primary target.
As mid-1942 approached, HYPO was under high pressure, and there are tales of 36-hour stints, of Rochefort working in his bathrobe and appearing for briefings late and disheveled besides. This effort climaxed in the last week of May with the decryption of enough JN-25 traffic to understand the Japanese attack plan at Midway in some, but not complete detail. This allowed Admiral Nimitz to gamble on the ambush which resulted in the Battle of Midway
Battle of Midway
The Battle of Midway is widely regarded as the most important naval battle of the Pacific Campaign of World War II. Between 4 and 7 June 1942, approximately one month after the Battle of the Coral Sea and six months after Japan's attack on Pearl Harbor, the United States Navy decisively defeated...
, the loss of four Japanese carriers and many naval aviators, and what is generally agreed to have been the turning point of the Pacific War.
Post-Midway transfers and changes
After Midway, disputes between Rochefort, on behalf of HYPO, and OP-20-G in Washington, together with some bureaucratic infighting in Washington, resulted in the removal of Rochefort from command of his Hawaii command and eventually in his assignment to command a drydock on the West Coast. He did no further crypto work for the rest of the war; many writers have expressed astonishment at thus discarding one of the two or three most qualified Navy cryptographic and Japanese language experts. Nimitz, when he learned of Rochefort's treatment some years later, was quite displeased.After having commandeered a girls' school in Washington (the Army took over one too), Naval Intelligence expanded greatly, as did OP-20-G, and HYPO became a smaller proportion of the total Navy signals intelligence effort in the Pacific.