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Station HYPO, also known as Fleet Radio Unit Pacific (FRUPAC), was the
United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...
signals monitoring and
cryptographic Cryptography, or cryptology (from "hidden, secret"; and ''graphein'', "to write", or '' -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adversarial behavior. More gen ...
intelligence unit in
Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...
during
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
. It was one of two major Allied signals intelligence units, called
Fleet Radio Unit Fleet Radio Units (FRU) 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 F ...
s in the Pacific theaters, along with
FRUMEL Fleet Radio Unit, Melbourne (FRUMEL) was a United States–Australian–British signals intelligence unit, founded in Melbourne, Australia, during World War II. It was one of two major Allied signals intelligence units called Fleet Radio Units in ...
in
Melbourne Melbourne ( , ; Boonwurrung language, Boonwurrung/ or ) is the List of Australian capital cities, capital and List of cities in Australia by population, most populous city of the States and territories of Australia, Australian state of Victori ...
,
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
. The station took its initial name from the phonetic code at the time for "H" for
Heʻeia, Hawaii Heeia () is a census-designated place comprising several neighborhoods located in the City & County of Honolulu and the Koʻolaupoko District on the island of Oʻahu north of Kāneʻohe. In Hawaiian the words ''heʻe ʻia'' mean "washed awa ...
radio tower. The precise importance and role of HYPO in penetrating the
Japanese naval codes 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. Every Japanese code was e ...
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 or "Office of Chief Of Naval Operations (OPNAV), 20th Division of the Office of Naval Communications, G Section / Communications Security", was the U.S. Navy's signals intelligence and cryptanalysis group during World War II. Its mission ...
Naval Intelligence section in Washington. Before the
attack on Pearl Harbor The attack on Pearl HarborAlso known as the Battle of Pearl Harbor was a surprise military strike by the Empire of Japan on the United States Pacific Fleet at Naval Station Pearl Harbor, its naval base at Pearl Harbor on Oahu, Territory of ...
of December 7, 1941, and for some time afterwards, HYPO was in the basement of the Old Administration Building at
Pearl Harbor Pearl Harbor is an American lagoon harbor on the island of Oahu, Hawaii, west of Honolulu. It was often visited by the naval fleet of the United States, before it was acquired from the Hawaiian Kingdom by the U.S. with the signing of the Reci ...
. 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 II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
were largely those related to
Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
. An early decision by OP-20-G in Washington divided responsibilities for them among
CAST Cast may refer to: Music * Cast (band), an English alternative rock band * Cast (Mexican band), a progressive Mexican rock band * The Cast, a Scottish musical duo: Mairi Campbell and Dave Francis * ''Cast'', a 2012 album by Trespassers William ...
at
Cavite Cavite, officially the Province of Cavite (; Chavacano: ''Provincia de Cavite''), is a Provinces of the Philippines, province of the Philippines located in the Calabarzon region. On the southern shores of Manila Bay and southwest of Manila, i ...
and then
Corregidor Corregidor (, , ) is an island located at the entrance of Manila Bay in the southwestern part of Luzon in the Philippines, and is considered part of Cavite City and thus the province of Cavite. It is located west of Manila, the nation's capi ...
, in the
Philippines The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...
, HYPO in Hawaii, and OP-20-G itself in Washington. Other Navy crypto stations, including
Guam Guam ( ; ) is an island that is an Territories of the United States, organized, unincorporated territory of the United States in the Micronesia subregion of the western Pacific Ocean. Guam's capital is Hagåtña, Guam, Hagåtña, and the most ...
and
Bainbridge Island Bainbridge Island is a city and island in Kitsap County, Washington, United States. It is located in Puget Sound. The population was 24,825 at the 2020 census, making Bainbridge Island the second largest city in Kitsap County. The island is se ...
on
Puget Sound Puget Sound ( ; ) is a complex estuary, estuarine system of interconnected Marine habitat, marine waterways and basins located on the northwest coast of the U.S. state of Washington (state), Washington. As a part of the Salish Sea, the sound ...
were tasked and staffed for signals interception and
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. In general, the greater the number of messages observ ...
. The US Army's
Signals Intelligence Service The Signal Intelligence Service (SIS) was the United States Army codebreaking division through World War II. It was founded in 1930 to compile codes for the Army. It was renamed the Signal Security Agency in 1943, and in September 1945, became t ...
(SIS) broke into the highest level Japanese diplomatic cypher (called
PURPLE Purple is a color similar in appearance to violet light. In the RYB color model historically used in the arts, purple is a secondary color created by combining red and blue pigments. In the CMYK color model used in modern printing, purple is ...
by the US) well before the attack on Pearl Harbor. PURPLE produced little of military value, as the
Japanese Foreign Ministry The is an executive department of the Government of Japan, and is responsible for the country's foreign policy and international relations. The ministry was established by the second term of the third article of the National Government Organiz ...
was thought by the
ultra-nationalists Ultranationalism, or extreme nationalism, is an extremist form of nationalism in which a country asserts or maintains hegemony, supremacy, or other forms of control over other nations (usually through violent coercion) to pursue its specific i ...
to be unreliable. Furthermore, decrypts from PURPLE, eventually called
MAGIC Magic or magick most commonly refers to: * Magic (supernatural), beliefs and actions employed to influence supernatural beings and forces ** ''Magick'' (with ''-ck'') can specifically refer to ceremonial magic * Magic (illusion), also known as sta ...
, 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 A conspiracy theory is an explanation for an event or situation that asserts the existence of a conspiracy (generally by powerful sinister groups, often political in motivation), when other explanations are more probable.Additional sources: * ...
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 and early 1942

HYPO was assigned responsibility for work on Japanese Navy systems, and after an agreement with
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
, the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...
and
Netherlands , Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...
to share the effort, worked with crypto groups based at
Melbourne Melbourne ( , ; Boonwurrung language, Boonwurrung/ or ) is the List of Australian capital cities, capital and List of cities in Australia by population, most populous city of the States and territories of Australia, Australian state of Victori ...
,
Hong Kong Hong Kong)., Legally Hong Kong, China in international treaties and organizations. is a special administrative region of China. With 7.5 million residents in a territory, Hong Kong is the fourth most densely populated region in the wor ...
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 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. Every Japanese code was e ...
by U.S. analysts. JN-25 was used by the IJN for high level operations: movement and planning commands, for instance. It was a state-of-the-art superencrypted
code In communications and information processing, code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form, sometimes shortened or secret, for communication through a communicati ...
, eventually a two-book system. Cryptanalytic progress was slow. Most references cite about 10% of messages partially (or sometimes completely) decrypted prior to December 1, 1941, at which time a new version of the system went into effect, requiring the cryptanalysts to start again. Although most references did set the limit of the percent of the messages that were decrypted at 10%, they were not privy to the latest information. Wilford in his ''Decoding Pearl Harbor: USN Cryptanalysis and the Challenge of JN-25B in 1941,'' suggests that this view is now untenable and that the JN-25 codes were readable to a great extent and hence, lends "support to the revisionist theories of Toland and Stinnett". 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 Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, also known historically as Ceylon, is an island country in South Asia. It lies in the Indian Ocean, southwest of the Bay of Bengal, separated from the Indian subcontinent, ...
and eventually
Kenya Kenya, officially the Republic of Kenya, is a country located in East Africa. With an estimated population of more than 52.4 million as of mid-2024, Kenya is the 27th-most-populous country in the world and the 7th most populous in Africa. ...
), 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 John Rochefort (May 12, 1900 – July 20, 1976) was an American naval officer and cryptanalyst. He was a major figure in the United States Navy's cryptographic and intelligence operations from 1925 to 1946, particularly in the Battle of M ...
, 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 The National Security Agency (NSA) is an intelligence agency of the United States Department of Defense, under the authority of the director of national intelligence (DNI). The NSA is responsible for global monitoring, collection, and proces ...
historian Frederick D. Parker:
By the middle of March 1942, two viable naval radio intelligence centers existed in the Pacific—one in Melbourne, Australia RUMEL 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.
Japanese traffic was intercepted regarding a new offensive operation being planned against a target only identified as AF. LCDR Wilfred J. Holmes at HYPO was responsible for the ruse which identified AF: a false report of a fresh water shortage on Midway was radioed in clear, evoking an
encrypted In cryptography, encryption (more specifically, encoding) is the process of transforming information in a way that, ideally, only authorized parties can decode. This process converts the original representation of the information, known as plain ...
Japanese response noting that AF was reporting water troubles; AF had to be Midway. 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 that resulted in the
Battle of Midway The Battle of Midway was a major naval battle in the Pacific Ocean theater of World War II, Pacific Theater of World War II that took place on 4–7 June 1942, six months after Japan's attack on Pearl Harbor and one month after the Battle of t ...
, the loss of four Japanese carriers and many naval aviators for much lower Allied losses, and what is generally agreed to have been the turning point of the Pacific War.


Post-Midway transfers and changes

In October 1942, after Midway, power struggles within the Navy resulted in the sidelining of
Laurance Safford Captain, U.S.N. Laurance Frye Safford (October 22, 1893 – May 15, 1973) was a U.S. Navy cryptologist. He established the Naval cryptologic organization after World War I, and headed the effort more or less constantly until shortly after th ...
, with the support of Admirals
Ernest King Ernest Joseph King (23 November 1878 – 25 June 1956) was a Fleet admiral (United States), fleet admiral in the United States Navy who served as Commander in Chief, United States Fleet (COMINCH) and Chief of Naval Operations (CNO) during Worl ...
and
Richmond K. Turner Admiral Richmond Kelly Turner (May 27, 1885 – February 12, 1961), commonly known as Kelly Turner, was an admiral of the United States Navy during the Second World War, where he commanded the Amphibious Force in the Pacific theater. Turner w ...
(and
Joseph Redman Joseph Reasor Redman (April 17, 1891September 7, 1968) was an admiral in the United States Navy. A naval communications officer, he played key roles in signals intelligence during World War II, while he served as Director of Naval Communications. ...
). Control of naval intercept and codebreaking was centralizing in
OP-20-G 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 U.S. Navy's signals intelligence and cryptanalysis group during World War II. Its mission ...
in Washington, where two new sections were headed by John R. Redman (Communications Combat Intelligence section) and Joseph Wenger (Communications Cryptanalytical section; to handle decryption and translation). Safford was shifted to an administrative support and cryptographic research role; so was sidelined for the remainder of the war (doing no further crypto work); as was
Joseph Rochefort Joseph John Rochefort (May 12, 1900 – July 20, 1976) was an American naval officer and cryptanalyst. He was a major figure in the United States Navy's cryptographic and intelligence operations from 1925 to 1946, particularly in the Battle of M ...
in Hawaii (he was assigned to command a dry-dock on the West Coast). After Midway, Rochefort was recommended for the
Distinguished Service Medal Distinguished Service Medal (DSM) is a high award of a nation, state or country. Examples include: *Distinguished Service Medal (Australia) (established 1991), awarded to personnel of the Australian Defence Force for distinguished leadership in act ...
to
Admiral Admiral is one of the highest ranks in many navies. In the Commonwealth nations and the United States, a "full" admiral is equivalent to a "full" general in the army or the air force. Admiral is ranked above vice admiral and below admiral of ...
Ernest King Ernest Joseph King (23 November 1878 – 25 June 1956) was a Fleet admiral (United States), fleet admiral in the United States Navy who served as Commander in Chief, United States Fleet (COMINCH) and Chief of Naval Operations (CNO) during Worl ...
. However, personal enmity from his chief of staff due to a prior passing encounter, and non-support from his immediate supervisors, led King to deny the award. Nimitz, when he learned of Rochefort's treatment some years later, was quite displeased. Rochefort was posthumously awarded the medal after a campaign by his intelligence officers galvanized Admiral D. "Mac" Showers and eventually CIA head
William Casey William Joseph Casey (March 13, 1913 – May 6, 1987) was an American lawyer who was the Director of Central Intelligence from 1981 to 1987. In this capacity he oversaw the entire United States Intelligence Community and personally directed the ...
to rectify the oversight. Having commandeered a girls' school in Washington (the Army took over one too), Naval Intelligence and OP-20-G expanded greatly. HYPO became a smaller proportion of the total Navy signals intelligence effort in the Pacific.


References


Bibliography

* * * * * *


External links

* {{cite web , url=http://www.navytv.org/channel.cfm?s=52&c=174 , title=Video interview with Donald M. Showers who was one of Rochefort's codebreaking team at Station HYPO in 1942 , website=Navy TV Cryptography organizations Signals intelligence of World War II Battle of Midway