Fleet Radio Units were the major centers for 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...

 cryptological and signals intelligence during the Pacific Campaign

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...

 of 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...

. Initially two FRUs were established in the Pacific, one 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...

, 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...

, called 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...

 or FRUPAC (Fleet Radio Unit, Pacific), and the other, called Station 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...

 or Belconnen, at Cavite Naval Yard

U.S. Naval Station Sangley Point

Naval Station Sangley Point was a communication and hospital facility of the United States Navy which occupied the northern portion of the Cavite City peninsula and is surrounded by Manila Bay, approximately eight miles southwest of Manila, the Philippines. The station was a part of the Cavite...

, 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...

, Philippines. With the fall of the Philippines to Imperial 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...

 forces in April and May 1942, CAST personnel were evacuated to a newly established FRU at Melbourne, Australia, called 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...

 (Fleet Radio Unit, Melbourne).

HYPO and FRUMEL supervised detached field units scattered at various locations and aboard ships throughout the south, central, and north Pacific areas until the end of World War II. A third center, NEGAT, was based at 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...

 headquarters in Washington DC. The entire cryptanalysis effort conducted by the units was called Operation Magic. Liaison between the units and with 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; the British signals intelligence center at Colombo

Colombo

Colombo is the largest city of Sri Lanka. It is located on the west coast of the island and adjacent to Sri Jayawardenapura Kotte, the capital of Sri Lanka. Colombo is often referred to as the capital of the country, since Sri Jayawardenapura Kotte is a satellite city of Colombo...

, Ceylon in 1942) was titled Copek.