OP-20-G facts for kids
Quick facts for kids 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 was a special group in the U.S. Navy during World War II. Its full name was "Office of Chief Of Naval Operations (OPNAV), 20th Division of the Office of Naval Communications, G Section / Communications Security." This group was in charge of signals intelligence and cryptanalysis. This means they listened to enemy radio messages, broke secret codes, and studied the information they found.
Their main job was to intercept, decode, and understand messages from the navies of Japan, Germany, and Italy. They also copied diplomatic messages from many other countries. A big part of their work focused on Japan, including breaking their early naval codes. This was possible thanks to listening stations and special direction-finding equipment across the Pacific, Atlantic, and in the U.S. They even had a school in Washington, D.C. to teach radio operators how to read Japanese telegraph codes.
Contents
How OP-20-G Started
The Code and Signal Section officially became part of the Division of Naval Communications (DNC) on July 1, 1922. It was named Op-20-G. In January 1924, a 34-year-old Navy lieutenant named Laurance F. Safford was given the job of expanding OP-20-G's work to include radio interception. He worked in the Navy Department building in Washington, D.C..
Japan was a main target for listening to radio messages and breaking codes. But there was a problem: finding people who could speak Japanese. The Navy had some officers who spoke Japanese well from working in Japan. However, there weren't enough radio operators who could read Japanese messages sent in kana (a Japanese writing system).
Luckily, some U.S. Navy and Marine radio operators in the Pacific had already started sharing notes on Japanese kana messages in 1923. Four of these men later became teachers. They taught others how to read kana messages when the Navy started classes in 1928.
The "On-The-Roof Gang"
These classes were taught by the team in Room 2426. The radio operators who learned these skills became known as the "On-The-Roof Gang." By June 1940, OP-20-G had grown to include 147 officers, enlisted men, and civilians. They were all connected to a large network of radio listening posts.
OP-20-G did some work on Japanese diplomatic codes. But their main focus was on Japanese military codes. The U.S. Navy first managed to understand Japanese naval codes in 1922. Navy agents secretly entered the Japanese consulate in New York City. They opened a safe, took pictures of pages from a Japanese navy codebook, and put everything back.
Before World War II, the Navy's code-breaking group worked from three main locations:
- Station NEGAT at the main office in Washington, D.C.
- Station HYPO (also called FRUPAC), a section at Pearl Harbor in Hawaii.
- Station CAST, a section in the strong caves of Corregidor island in the Philippines. This station had codebreakers and a network of listening and radio direction-finding stations.
- FRUMEL was set up in Melbourne, Australia. This happened when Navy intelligence staff from the Philippines moved there.
Working with Other Groups
The U.S. Army's Signal Intelligence Service (SIS) and OP-20-G sometimes had problems working together. They competed to give their secret intelligence, called "MAGIC," to high-ranking officials. It was even more complicated because the Coast Guard, the FBI, and the FCC also had their own radio-intercept operations.
In 1940, SIS and OP-20-G agreed on rules for handling "MAGIC" information. The Army was in charge on even-numbered days, and the Navy on odd-numbered days. This meant the Navy took over just after midnight on December 6, 1941.
However, there were often delays or problems in using the "MAGIC" information. There wasn't a good system for organizing and understanding all the intelligence. This led to issues that were only fixed after the war with a single intelligence agency.
The Attack on Pearl Harbor
In the early morning of December 7, 1941, the U.S. Navy listening station at Fort Ward in Washington picked up a radio message. It was from the Japanese government to its embassy in Washington, D.C. This was the last of 14 messages sent over the past 18 hours.
These messages were decoded by a special machine called a PURPLE machine at OP-20-G. They were then given to the Army's SIS for translation from Japanese. This happened early on December 7. Army Colonel Rufus S. Bratton and Navy Lieutenant Commander Alwin Kramer both looked at the decoded messages.
The messages told the Japanese ambassador in Washington to inform the U.S. Secretary of State, Cordell Hull, at 1:00 PM Washington time that talks between the United States and Japan were over. The embassy was then told to destroy their cipher machines. This sounded like war. Although the message didn't mention any specific military action, Kramer realized that the sun would be rising over the Pacific Ocean at that time. Both men tried to contact Army Chief of Staff General George C. Marshall.
After some frustrating delays, General Marshall received the decoded messages. He understood how important they were and sent a warning to commanders in the field, including Major General Walter Short in Hawaii. However, Marshall didn't want to use the phone because it wasn't very secure. So, he sent the warning through slower channels. Because of various problems and mistakes, General Short received the message many hours after Japanese bombs had already hit the U.S. Navy fleet at Pearl Harbor.
After Pearl Harbor
In February 1942, some changes happened within the Navy. Laurance Safford was moved to a different role. Admirals Ernest King and Richmond K. Turner wanted to bring all naval listening and code-breaking work under one central control in Washington. So, two new sections were created. John R. Redman led the Communications Combat Intelligence section, and Joseph Wenger led the Communications Cryptanalytical section, which handled decoding and translation. Safford was given a support role for the rest of the war.
As the Japanese forces advanced in the Philippines and the demand for intelligence grew, OP-20-G took two main steps:
- The staff and services from CAST were moved to a new station called FRUMEL in Melbourne, Australia. This station was a joint effort between the U.S., Australia, and Britain.
- Another intelligence center, called NEGAT, was formed in Washington. It used parts of the OP-20-G headquarters.
In the summer of 1942, the Navy considered moving OP-20-G to the same location as the Army's SIS. However, Commander Joseph Wenger found a "perfect new home" for the growing OP-20-G. He bought a private girls' school, Mount Vernon College for Women, for $800,000. On February 7, 1943, it opened as the "Naval Communications Annex," and staff moved in over the next two months.
How OP-20-G Changed Over Time
The name and role of OP-20-G changed several times over the years:
- July 1922-March 1935: Code and Signal Section (Op-20-G), Division of Naval Communications (DNC).
- March 1935-March 1939: Communications Security Group (Op-20-G), DNC.
- March 1939-September 1939: Radio Intelligence Section (Op-20-G), DNC.
- October 1939-February 1942: Communications Security Section (Op-20-G), DNC.
- February 1942-October 1942: Radio Intelligence Section (Op-20-G), DNC.
- October 1942-July 1946: Communications Intelligence Organization (Op-20-G), DNC.
- July 10, 1946: All Navy communications intelligence groups were combined. They were then called "Communications Supplementary Activities" of the 20th Division of the Office of Naval Communications, Section 2, (Op-20-2).
