OP-20-G
OP-20-G | |
---|---|
Active | July 1, 1922 - July 10, 1946 |
Allegiance | United States |
Branch | United States Navy |
Type | Code and Signal Section |
Role | Signals intelligence Cryptanalysis |
Garrison/HQ | Navy Department building, Washington, D.C. |
Commanders | |
Notable commanders | Captain Laurance Safford Captain Joseph Rochefort Captain John R. Redman |
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 was to intercept, decrypt, and analyze naval communications from Japanese, German, and Italian navies. In addition OP-20-G also copied diplomatic messages of many foreign governments. The majority of the section's effort was directed towards Japan and included breaking the early Japanese "Blue" book fleet code. This was made possible by intercept and High Frequency Direction Finder (HFDF) sites in the Pacific, Atlantic, and continental U.S., as well as a Japanese telegraphic code school for radio operators in Washington, D.C.
Prewar
The Code and Signal Section was formally made a part of the Division of Naval Communications (DNC), as Op-20-G, on July 1, 1922. In January 1924, a 34-year-old U.S. Navy
Japan was of course a prime target for
transmissions. Four of these men became instructors in the art of reading kana transmissions when the Navy began conducting classes in the subject in 1928.The classes were conducted by the Room 2426 crew, and the radiotelegraph operators became known as the "On-The-Roof Gang". By June 1940, OP-20-G included 147 officers, enlisted men, and civilians, linked into a network of radio listening posts as far-flung as the Army's.
OP-20-G did some work on Japanese diplomatic codes, but the organization's primary focus was on Japanese military codes. The
Before the war, the Navy cipher bureau operated out of three main bases:
- Station NEGAT at headquarters in Washington, D.C.
- Station HYPO (or FRUPAC), a section at Pearl Harbor in Hawaii
- Station CAST, a section in the fortified caves of the island of Corregidor, in the Philippines, with codebreakers and a network of listening and radio direction finding stations.
- FRUMEL was established in Melbourne when Navy signals intelligence personnel from the Philippines were evacuated to Australia. Evacuated Army signals intelligence personnel went to the Central Bureau.
The
The Navy organization at OP-20-G was more conventionally hierarchical than the Army at
In 1940, SIS and OP-20-G came to agreement with guide lines for handling MAGIC; the Army was responsible on even-numbered days and the Navy on odd-numbered days. So, on the first minute after midnight on 6 December 1941 the Navy took over. But USN Lt-Comdr
The result was that much of the MAGIC was delayed or unused. There was no efficient process for assessing and organizing the intelligence, as was provided postwar by a single intelligence agency.
Attack on Pearl Harbor
In the early hours of the morning of 7 December 1941, the
The messages were decrypted by a
The decrypts instructed the Japanese ambassador to Washington to inform the US Secretary of State, Cordell Hull, at 1:00 PM Washington time that negotiations between the United States and Japan were ended. The embassy was then to destroy their cipher machines. This sounded like war, and although the message said nothing about any specific military action, Kramer also realized that the sun would be rising over the expanses of the central and western Pacific by that time. The two men both tried to get in touch with Army Chief of Staff General George C. Marshall.
After some agonizing delays, Marshall got the decrypts and methodically examined them. He realized their importance and sent a warning to field commanders, including Major General
After Pearl Harbor
In February 1942 power struggles within the Navy resulted in the sidelining of
With
- The staff and services of CAST were progressively transferred to a newly formed US-
- Another signals intelligence center, known as NEGAT was formed in Washington, using elements of OP-20-G headquarters.[4]
In Summer 1942 the Navy went through the motions of perhaps co-locating with the Army's SIS but Commander
Section evolution
- (July 1922-March 1935) Code and Signal Section (Op-20-G), Division of Naval Communications (DNC), OCNO (July 1922-March 1935).
- (March 1935-March 1939) Communications Security Group (Op-20-G), DNC, OCNO
- (March 1939-September 1939) Radio Intelligence Section (Op-20-G), DNC, OCNO
- (October 1939-February 1942) Communications Security Section (Op-20-G), DNC, OCNO
- (February 1942-October 1942) Radio Intelligence Section (Op-20-G), DNC, OCNO
- (October 1942-July 1946) Communications Intelligence Organization (Op-20-G), DNC, OCNO
- July 10, 1946 All Naval communications intelligence elements were collectively designated "Communications Supplementary Activities" of the 20th Division of the Office of Naval Communications, Section 2, (Op-20-2)
See also
- Andrew Gleason, one of the OP-20-G members during World War II
- Fleet Radio Unit
- United States Naval Computing Machine Laboratory
- US Army SIS
- United States Coast Guard Unit 387
References and further reading
- ^ Budiansky 2000, pp. 228–229.
- ^ Clausen 1992, pp. 45, 307, 308.
- ^ Layton 1985, pp. 367, 368.
- ^ a b Parker, Frederick D. A Priceless Advantage: U.S. Navy Communications Intelligence and the Battles of Coral Sea, Midway, and the Aleutians. Fort Meade MD: Center for Cryptologic History, National Security Agency, 1993.
- ^ a b Budiansky 2000, pp. 223–226.
- Budiansky, Stephen (2000). Battle of Wits: The complete story of Codebreaking in World War II. New York: Free Press. ISBN 0-684-85932-7.
- ISBN 0-517-58644-4.
- ISBN 0-688-04883-8.
External links
- "The Pacific War: The U.S. Navy, Naval Intelligence as of Pearl Harbor". Retrieved 2006-12-07.
- "The National Archives: Records of the National Security Agency/Central Security Service". Retrieved 2006-12-07.