Early in 1924, the Chief of Naval Operations (CNO), Admiral Edward W. Eberle, encouraged the Commander in Chief, Asiatic Fleet (CINCAF), Admiral Thomas Washington, to expand radio intelligence facilities in his area. As a result of this encouragement, in 1924, the first shore-based intercept station was established in the American consulate in Shanghai. Its primary target was the diplomatic radio network serving the numerous Japanese consulates throughout China. Shanghai also copied both Naval and commercial traffic (Japanese and British).

OP-20-G received all intercept logs, including traffic and messages for cryptanalysis via courier, usually every three months. After the codes were broken and the messages reduced to plain text, the contents were then sent to the Officer of Naval Intelligence (ONI) where, if necessary, they were translated into English.  Early on, most of the communication intercepted within China was plain language (plain-text).

In 1927, this network became the prime target of Marine Corps operators that were initially trained by Navy operators at Shanghai.

Originally designated, in the phonetic alphabet of the time, Station Able, their unit was disestablished eight years later when both the Japanese threat to the city became too pressing and personnel limitations caused the Marine Corps to withdraw completely from intercept work. Responsibility for the diplomatic network was shifted to the headquarters of the Fourth Marine Regiment in Shanghai, which possessed an enclave of career Navy intercept operators trained in Japanese traffic. Their unit became the new Station Able. Shanghai Station transferred to Station Ship Shanghai in March, 1927; and disestablished in March, 1929. The “Station Ship” was probably USS Monocacy (PG-20), reclassified as PR-4 on June 15, 1928).
The Communications Radio Intelligence units monitoring the Japanese fleet maneuvers were at Libugon, Guam; Olongapo, Philippines (July, 1930 to February, 1935, when the unit moved to Los Banitos, Mariveles, Philippines); Peking (Peiping), China (1927 to July, 1935, when the unit moved to Shanghai, China); Los Banitos, Mariveles, Philippines (March 1, 1935 to January, 1936), the USS Goldstar (AG-12), and the USS Augusta (CA-31) (Asiatic Fleet Flagship from November 9, 1933 to November 22, 1940). Mobile detachments from shore stations in the Philippines and Guam manned communications radio intelligence positions onboard the USS Augusta and USS Goldstar.
In December 1940, Station Able in Shanghai, China was closed. Station Able’s mission and personnel were transferred to Station C, which had been established in a special tunnel built for the Navy at Monkey Point on Corregidor, in the Philippines.
Time Line:

1923 – CNO requests Fleet Forces listen in on enciphered foreign traffic

1924 – RIP-5 Kana typewriter designed and 4 ordered

1924 – First intercept station established in U.S. Consulate Shanghai

1924 March – 1927 – Communications Radio Intelligence Unit, Radio Security Station Shanghai, China at U.S. Consulate

1925 – DNC requested DCO 14th Naval District (Pearl Harbor) assign one operator to copy Japanese diplomatic traffic

1927 – Intercept station established at Peking to copy Japanese diplomatic traffic

March 1927 – Moved Station to USS Monocacy (PG-20)

1927 – July 1935 – Communications Radio Intelligence Unit, Radio Security Station, Peking (Peiping), China (Marine Detachment) – Mission moved to Shanghai, July 1935

March 1929 – Communications Radio Intelligence Unit, Radio Security Station, Shanghai (Station Ship), USS Monocacy (PG-20) March 1927 – Moved to Libugon, Guam, March 1929

July 1935 – December 1940 – Communications Radio Intelligence Unit, Radio Security Station, Shanghai, China (4th Marine Regiment) – Moved to Corregidor December 1940

**December 1940 – April 1942 – Communications Radio Intelligence Unit, Corregidor, Luzon, Philippines – Evacuated to Melbourne, Australia, April 1942

Communications Radio Intelligence Unit, Melbourne New South Wales, Australia, May 1942 – 01 November 1945 at Naval Supplementary Radio Station Moorabbin, Melbourne, Australia.

** StationHYPO will have a five part series on Corregidor (4-8 April).

Sources:

navycthistory.com
NCVA, CTRCM John “Gus” Gustafson, USN-Ret
Edited by Mario Vulcano