Station CAST
Encyclopedia
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 Japanese communications as the War expanded from China into the rest of the Pacific theaters
. As Japanese advances in the Philippines
threatened CAST, its staff and services were progressively transferred to Corregidor in Manila Bay, and eventually to a newly formed US-Australia
n station, FRUMEL
in Melbourne
, Australia.
STATION CAST had originally been located at Shanghai but had been evacuated to Cavite in early 1941 as part of the US Navy's disengagement with China.
Prior to the war, CAST was the US Navy's Far East cryptographic operation, under the OP-20-G
Naval Intelligence section in Washington. It was located at the Navy Yard in Manila
and moved into the tunnels on Corregidor
, as Japanese attacks increased. STATION CAST possessed one of the PURPLE machines produced by the US Army.
Cryptanalytic problems facing the United States in the Pacific prior to World War II were largely Japan
ese. An early decision by OP-20-G divided responsibility for Japanese cryptanalysis amongst its various stations. Station CAST (at Manila in the Philippines), Station HYPO
(Pearl Harbor
, Hawaii
), and OP-20-G
itself in Washington, shared cryptanalytic duties. Other Stations (on Guam
, in Puget Sound
on Bainbridge Island, Guam
, etc.) were tasked and staffed for signals interception and traffic analysis.
by US analysts) produced very interesting intelligence, but very little of military value, indeed no tactical value, and not much more of direct political value as the Foreign Office in Japan was thought by the ultra-nationalists in effective charge of Japanese foreign and military policy, to be unreliable. Furthermore, decrypts from PURPLE
traffic, eventually called MAGIC
, were rather capriciously distributed to high level officials in Washington, and in general, poorly used. SIS was able to build several PURPLE machine equivalents and the distribution of those machines has since been thought controversial. One was sent to Station CAST. After the US entered the War, two went to Bletchley Park
, the center of British cryptographic work. One was sent to the Far East Combined Bureau
(FECB) at Singapore, and was lost during the fall of Singapore
) and Batavia
(Kamer 14 or Room 14).
Prior to the attack on Pearl Harbor
, the amount of available traffic was low, and little progress had been made on the most important Japanese Navy system, called by US analysts JN-25
. JN-25 was used for high level operations: movement and planning commands, for instance. It was a superencrypted code, eventually a two-book system, and joint cryptanalytic progress was slow. JN-25B was introduced on 1 December 1940, but was broken immediately by FECB as the additives were not changed. Most references cite about 10% of messages partially (or sometimes completely) decrypted prior to 1 December 1941, at which time a new edition of the system went into effect and sent all the cryptanalysts back to the beginning.
After 7 December 1941, there was considerably more JN-25 traffic as the Japanese Navy operational tempo increased and geographically expanded, and progress against it went better. The FECB contribution stopped until the crypto station could be relocated from Singapore to Ceylon, but CAST, HYPO, and the Dutch at Batavia, in conjunction with OP-20-G, made steady progress.
punched card
machines are said to have been among the gear shoved into the harbor) and were evacuated by submarine to Australia, for service with FRUMEL
. Some personnel also worked at the Central Bureau
, supplying signals intelligence to MacArthur's South West Pacific Area (command).
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 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,...
at Cavite Navy Yard 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...
, until Cavite was captured by the Japanese forces
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...
in 1942, 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 an important part of the 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...
intelligence effort, addressing Japanese communications as the War expanded from China into the rest of 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...
. As 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....
threatened CAST, its staff and services were progressively transferred to Corregidor in Manila Bay, and eventually to a newly formed US-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...
n station, 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.
STATION CAST had originally been located at Shanghai but had been evacuated to Cavite in early 1941 as part of the US Navy's disengagement with China.
Prior to the war, CAST was the US Navy's Far East cryptographic operation, under 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 at the Navy Yard in Manila
Manila
Manila is the capital of the Philippines. It is one of the sixteen cities forming Metro Manila.Manila is located on the eastern shores of Manila Bay and is bordered by Navotas and Caloocan to the north, Quezon City to the northeast, San Juan and Mandaluyong to the east, Makati on the southeast,...
and moved into the tunnels on 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...
, as Japanese attacks increased. STATION CAST possessed one of the PURPLE machines produced by the US Army.
Cryptanalytic problems facing the United States in the Pacific prior to World War II were largely 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...
ese. An early decision by OP-20-G divided responsibility for Japanese cryptanalysis amongst its various stations. Station CAST (at Manila in the Philippines), Station HYPO
Station HYPO
Station 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...
(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...
, 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...
), and 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...
itself in Washington, shared cryptanalytic duties. Other Stations (on 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...
, in 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...
on Bainbridge Island, 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...
, etc.) were tasked and staffed for signals interception and traffic analysis.
PURPLE diplomatic traffic
The US Army SIS break into the highest security Japanese diplomatic cypher (called PURPLEPURPLE
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 US analysts) produced very interesting intelligence, but very little of military value, indeed no tactical value, and not much more of direct political value as the Foreign Office in Japan was thought by the ultra-nationalists in effective charge of Japanese foreign and military policy, to be unreliable. Furthermore, decrypts from 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...
traffic, 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 rather capriciously distributed to high level officials in Washington, and in general, poorly used. SIS was able to build several PURPLE machine equivalents and the distribution of those machines has since been thought controversial. One was sent to Station CAST. After the US entered the War, two went to Bletchley Park
Bletchley Park
Bletchley Park is an estate located in the town of Bletchley, in Buckinghamshire, England, which currently houses the National Museum of Computing...
, the center of British cryptographic work. One was sent to the Far East Combined Bureau
Far East Combined Bureau
The Far East Combined Bureau, an outstation of the British Government Code and Cypher School, was set up in Hong Kong in March 1935, to monitor Japanese, and also Chinese and Russian intelligence and radio traffic...
(FECB) at Singapore, and was lost during the fall of Singapore
Japanese Navy crypto systems: JN-25
Stations HYPO and CAST were assigned responsibility for work on Japanese Navy systems, and after the agreement with the United Kingdom and Netherlands to share the effort, worked with crypto groups in Hong Kong then Singapore (Far East Combined BureauFar East Combined Bureau
The Far East Combined Bureau, an outstation of the British Government Code and Cypher School, was set up in Hong Kong in March 1935, to monitor Japanese, and also Chinese and Russian intelligence and radio traffic...
) 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...
(Kamer 14 or Room 14).
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...
, the amount of available traffic was low, and little progress had been made on the most important Japanese Navy system, called by US analysts 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...
. JN-25 was used for high level operations: movement and planning commands, for instance. It was a superencrypted code, eventually a two-book system, and joint cryptanalytic progress was slow. JN-25B was introduced on 1 December 1940, but was broken immediately by FECB as the additives were not changed. Most references cite about 10% of messages partially (or sometimes completely) decrypted prior to 1 December 1941, at which time a new edition of the system went into effect and sent all the cryptanalysts back to the beginning.
After 7 December 1941, there was considerably more JN-25 traffic as the Japanese Navy operational tempo increased and geographically expanded, and progress against it went better. The FECB contribution stopped until the crypto station could be relocated from Singapore to Ceylon, but CAST, HYPO, and the Dutch at Batavia, in conjunction with OP-20-G, made steady progress.
CAST during and after the invasion of the Philippines
Station CAST and its personnel and equipment were moved from Manila to the tunnels on Corregidor as the Japanese approached and spent the next months working there. Eventually, they destroyed their equipment (some IBMIBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
punched card
Punched card
A punched card, punch card, IBM card, or Hollerith card is a piece of stiff paper that contains digital information represented by the presence or absence of holes in predefined positions...
machines are said to have been among the gear shoved into the harbor) and were evacuated by submarine to Australia, for service 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...
. Some personnel also worked at the Central Bureau
Central Bureau
The Central Bureau was one of two Allied Sigint organisations in the South West Pacific area during World War II. Central Bureau was attached to the HQ of the Allied Commander of the South West Pacific area, Douglas MacArthur. The other unit was the joint RAN/USN Fleet Radio Unit, Melbourne ,...
, supplying signals intelligence to MacArthur's South West Pacific Area (command).