The 23-year period between WWI and WWII, OP-20-G had a real sense of urgency to build a communications intelligence (COMINT) capability to support decision makers with actionable intelligence information. To many in OP-20-G, as well as senior military leaders, it was clear years before the surprise attack on Pearl Harbor that the United State and Japan will go to war. In the years leading up Pearl Harbor, OP-20-G was attempting every possible way to collect, analyze and report on this growing threat.  At the time COMINT was the primary means of intelligence information.

On the featured image starting on the upper left corner, going clock wise is CAPT Laurence F. Safford, Ms. Agnes Meyer Driscoll, CAPT Joseph N. Wenger, Dorman, A. Chauncey, LT Joseph . Rochefort, CAPT George McGinnis, CRM Harry Kidder, CRM Walter McGregor, CAPT Jack S. Holtwick, and CAPT Thomas Dyer.

This time-line below shows how OP-20-G prepared for war.  Please note this is not an exhaustive time-line.


July 28, 1914: Start of WWI

28 July 1916: The US Navy Code and Signal Section was established.

November 11, 1918: WWI Ends

1918: Office on Naval Intelligence (ONI) acquired spaces in the sixth wing of the Navy Headquarters Building on Constitution Avenue in the District of Columbia for the Code and Signal Section.  The department consisted of 13 officers, 14 males enlisted and 34 “yeomanettes,” a term used at that time for enlisted women.  In addition to developing and distributing cryptographic systems, this small group had the responsibility to oversee fleet callsign assignments.

June 1918: Agnes Meyer enlisted in the United States Navy as chief yeoman and was assigned to the Code and Signal Section of the Director of Naval Communications (DNC).

May 19, 1919: Black Chamber Created.  This was a joint endeavor between the War and State Departments.  Created as the Commercial Code Compiling Co. in New York City, this new organization unofficially was dubbed the “New York Office,” or “Black Chamber.”

1921: ONI covertly acquired a photographic copy of the “Imperial Japanese Navy Secret Operating Code-1918.”

1921: An interest to develop a capability among the fleet radioman to intercept Japanese kata-kana was expressed by the Commander Battleship Force, Pacific Fleet, though very little came of it at the time.

1922: The Research Desk (cryptanalysis) of the Code and Signal Section came into existence as a part of Director of Naval Communications (DNC) with one officer and four civilians assigned.

July 1922: Formally established the cryptologic element Communication Security Unit, or DNC OP-20-G.

1923: CNO/ONI requests Asiatic and Pacific Fleet Forces to listen in on enciphered foreign traffic.

1923: Agnes Meyer left the navy to work for the Hebern Electric Code Company as a technical advisor.

1924: LT Laurance Frye Safford one of the first U.S. Naval officers to specialize in the field of cryptology headed the newly established Cryptographic Research Desk in the OPNAV Code and Signal Section (OP-20-G).

1924: Agnes Meyer returned to the navy as a civilian.

Mid-1920s: Radiomen on Asiatic duty assignments on the USS ISABEL (PY 10), USS PITTSBURGH (CA 4), and the men in the 4th Marine Headquarters at Shanghai, China, had self-trained themselves to intercept radio traffic (kata kana) that was transmitted on Japanese Navy radio circuits.

March 1924: First shore-based intercept site established at U.S. Consulate in Shanghai, China for the purpose of copying “Orange” radio traffic.  The arbitrary color orange was used in U.S. Naval War Plans to designate Japan.

1924: LT Safford used a secret ONI fund to purchase four Underwood Code Machine (later named RIP-5) typewriter at a cost of $645.00.  Three of these were quickly sent to the Asiatic Fleet with recommendations that they be supplied to Naval Radio Station Shanghai, USS HURON (ID 1408), (Flagship for the Asiatic Fleet) and USS PRUITT (DD 347).

July 1924: LT Safford initiated a search for possible Cryptographic Research Desk candidates from the fleet and would post monthly Communication Division Bulletin using cryptograms of varying difficulty. Individuals who successfully completed these puzzles and indicated by their correspondence an interest in cryptography had their names placed in a personnel file for future contact. The first pupil to come to Safford for training, in 1924, was ENS Joseph N. Wenger.

1925: Second shore-based intercept site established at Wailupe, Hawaii.

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

October 1925 to January 1926: Safford first training class comprised of five students: LT Clarence V. Lee, LTjg  Joseph J. Rochefort, LTjg Warren K Sherman, LTjg Frederick D. Kime and Capt L. F. S. Horan, USMC.  However, the Marine Officer never received a COMINT assignment.

In 1926: ONI finished translating the 1918 Japanese Navy code book, acquired in 1921.  Code book updates were obtained, again covertly, in 1926 and in 1927.  Given the cover-name “Red Book,” the translation was turned over to the DNC.

1926: Safford rotated out for sea duty and was replaced on the Research Desk by LT Joseph Rochefort. In turn, Rochefort was replaced in September 1927 by LT Bern Anderson. Safford returned from sea duty to the Research Desk in August 1929.

June 23, 1926: LT Rochefort reported in a memorandum “The Navy has two intercept stations worthy of the name.” One of these was located at Wailup, Hawaii (East of Diamond Head on Oahu) and the second in Shanghai, China.  The Hawaiian station was manned by Chief in Charge, D. A. Chauncey, CRM R. E. Milner, and RM1 Coonce.   Only RM2 J. C. Duvall is listed among the six radiomen assigned in Shanghai.  Other sites noted in the memorandum where intercept was being attempted were located in Peiping, Guam, San Francisco, and onboard USS BITTERN.

March, 1927: Although five marines were ordered to Peiping via Shanghai, the Shanghai station was transferred to the local station ship that same year.  Two years later Shanghai was disestablished due to the transfer of the radiomen to general service billets.  CRM Lyons was an exception; he received orders to Guam in 1929. The “Station Ship” was probably USS GENERAL ALAVA (AG 5) or USS MONOCACY (PG 20).

1927: LCDR E. M. Zacharias, while assigned to the American Consulate in Shanghai was given temporary command of USS McCORNICK (DD 223) for the purpose of moving the ship from Chefoo, China to Hong Kong.  En route, he took with him the following intercept operators: CRM E. J. Cornall, RM1 M. A. Malloy, RM2 M. W. Fallbee, RM2 F. W. Kodzeski, and RM1 H. W. Sauer and equipment – presumably to test the viability of shipboard intercept.  A year later, he proposed to ONI that a shipboard intercept team be dispatched to monitor the 1927 Japanese Navy’s Grand Maneuvers.  Permission was granted.  Although reports of this first effort to copy the radio communications of the Japanese naval maneuvers are not available, conclusions offered by LCDR Zacharias indicate they successfully monitored fleet operations without the benefit of visual sightings.

September 20, 1927:  William Kiser, Paul KIugler, William Thomson, Ogden Wilson, and Winnett Robinson, USMC, transferred to from Shanghai to Peiping.

October 1927: CRM Dorman Chauncey arrived in Peiping and established the station.

May 8, 1928:  CINCAF reported he had available to him only nine operators qualified to copy Orange (Japanese) radio traffic.  Those qualified were: CRM’s E.J. Cornall, Dorman A. Chauncey; RM1’s M. A. Molloy, H. W. Falbee, Malcolm W Lyon; RM2’s J. G Duvall, F. W. Kodzeski, and RM3’S H. W. Saucer and J. R Shannon.  Two months after this letter, the CNO announced the establishment of a school to be held at the Navy Department to instruct radio operator in intercept work.

September 1928: Marines William Kiser and Winnett Robinson were assigned “spec temp det d” on the USS Memphis (CL 13).  CRM Chauncey, Marines Paul Kugler and Ogden Wilson were assigned to the USS Trenton (CL 11).  They remained on board for most of September.

October 1, 1928: The first class was held for specially selected enlisted Navy and Marine Corps radio operators – On the Roof Gang (OTRG).

January 1929: The first class of On-The-Roof (OTR) graduated with CRM Harry Kidder as instructor.  Those completing the course were: CRM Joseph Goldstein, CRM Guy Oliver Billehus, RM1 Keith E. Goodwin, RM1 Martin A. Vandenburg, RM1 B. E. Cloyd, RM1 R. W. Hoffman, and RM1 Truett C. Lusk.  Following graduation all seven were sent to Guam.

March 1929: CRM Lyons established an intercept site on Guam.  This operator was transferred from Shanghai China. Within a year, the lone interceptor was joined by seven OTR gang graduates.

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

March, 1929: Shanghai Station was disestablished.

May 13, 1929: CNO recognized the need for radio intelligence and indicated his intention to establish a radio intelligence office with the Asiatic Fleet and to organize cryptanalytic units afloat.

October 1929: CRM Joseph Goldstein and RM1 Truett Lusk were detached from the USS ISABEL during to survey several possible sites in the Philippines.  This set in motion the selection of Olongapo Navy Yard as station “C” because of good physical security and the proximity to support facilities.

1930: Japanese Grand Maneuvers. A larger numbers of intercept operators enabled the U.S. fleet to copy a considerable volume of radio traffic from the Japanese fleet’s 1930 Grand Maneuvers. The traffic was forwarded to Washington (OP-20-G), where it was worked on by LCDR Safford, LT. Wenger and Mrs. Driscoll. These messages revealed Japan’s battle plan against the United States, Japanese fleet mobilization procedures, and Japanese plans for defense of the western Pacific. The surprised Americans also learned that the Japanese had an excellent grasp of American war plans for the Pacific.

1930: DNC, Captain Stanley C. Hooper sent OP-20-G a memorandum suggesting the use of tabulating machines for “mechanical labor” for use in counting frequency distributions and repetitions. LCDR Safford and Ms. Driscoll dismissed it as unfeasible due to the unpredictable nature of ciphers. Captain Hooper, however, did not let the matter drop and arranged for LT Wenger to attend demonstrations of modern office equipment. This Tabulating Machine Company later became the IBM Corporation.

June 23, 1930: Letter to the Commandant, First Naval District, CNO proposed to add one radiomen billet at Bar Harbor, Maine. The following month RM1 Clifton Shumaker was order into the billet.

July, 1930 to February, 1935: The Communications Radio Intelligence units at Libugon, Guam; Olongapo, Philippines were able to monitor the Japanese fleet maneuvers.

January 1931: Experimental HFDF (Rotating Adcock) commissioned was at Naval Research Laboratory.

June 1, 1931: US Coast Guard established a Cryptanalytic Section.

December 1931: 24 fleet radiomen and ten marines had successfully completed the “On-The-Roof” intercept training program.

1932: Marines Corps announced they had nine qualified operators in or en route Peiping.

February 1932: The Naval ROTC units operating at Yale, Harvard, Northwestern, Georgia Tech, California, and Washington were asked to seek five talented individuals who could be offered further training in the field of cryptanalysis.

February 23, 1932: The Research Desk as able to report that 23 Navy radiomen were qualified and performing radio intercept duties.

1932: RM2 James (Little Jimmy) Pearson boarded a Dollar Line Passenger ship in Seattle Washington.

July 1932: CINCAF noted in a letter to CNO, that there were but three intercept operating sites available to him: Peiping, Guam and the flagship, USS PITTSBURGH. No mention is made of the RI facilities of Shanghai.

20 December 1932 – January 5, 1933: Guam – Original intercept facility established in building #62 in the palace grounds on the U. S. Naval Station in the city of Aciana. The site was later moved to building #84.

June 1933: Experimental HFDF developed by Naval Research Laboratory and Bell Laboratories.

July 1933: Intercept equipment was sent to Heeia, Hawaii.

August 1933: CNO directs HFDF be installed in 1st and 12th Naval districts

May 1933 – June 1934: American Presidential Liner provides rooms, meals and transportation to AG and RM for approximately one Year’s time.

June-August 1933: Japanese Ground Maneuvers. LT Joseph Wenger compiled all the American intercept of that year’s Japanese fleet maneuvers, and, through traffic analysis over a period of six months, produced a report on the composition of the Japanese fleet. The results of three years of cryptanalysis on the same messages eventually proved Wenger’s list correct.

Summer 1934: OP-20-G had five officers undergoing training: LTjg’s R. H. Linsley, A. L. Glick, S. J. McKee, J. S. Holtwich, and L. W. Parke.

1934: The Japanese Navy started using machine cipher.  Mrs. Driscoll was able to penetrate the system using manual methods.  A year later, LTjg Holtwick devised an electro-mechanical system which would decrypt the message once the key had been solved.  LT Wenger, then head of the Research Desk, approved the designed and had the machine shop at the Naval Gun Factory, Washington D. C. manufacture a prototype model.

Mid 1934: A new desk was set up at the Code and Signals Section called the Radio Intercept Desk (GX).  At the same time the Research Desk (cryptanalysis) was redesigned GY.

October 15, 1934: USS Gold Star (AK 12) was directed to transfer a RF receiver to Guam.

February 27, 1935: LT Goodwin reported intercept watches were discontinued at Olongapo, Philippines.

March 1, 1935 to January, 1936: Established intercept watches at the Navy Camp, Mariveles.

March 11, 1935: OP-20G became the “Communication Security Group.”

July 1935 – December 1940: The Navy site at Peking (Peiping) China (Station ABLE) closed and operations transferred to Shanghai (4th Marine Regiment) with eight marines under the leadership of a Chief Radioman. This was done primarily for security and to expedite the transport of intercept.

January 6, 1936:  Due to the physical isolation and the danger of Sakdalist uprisings, the intercept site at Marivels was moved by barge to Cavite Navy Yard.

December 1936: Three Kana typewriters (RIP-5) were sent to Guam.

1937: Japanese military forces moved into North China occupying sections of Shanghai.  This invasion created a tense period for the 4th Marines Regiment.  LT Lamb, then on the CINCAF staff, moved from the flagship to Station A (Shanghai), joining Captain Zern USMC.  The situation in China also added pressure on the need to establish a safer site on Corregidor.

July 1937: HFDF intercept site at Guam was commissioned and became the Navy’s second “intelligence” DF station, the first being Cavite, Philippines.

1938: The German Navy was beginning to demonstrate its military might in the Atlantic.  To prepare for his challenge, new RIP-5s were designed with German characters in place of Japanese and a small Radio Intercept Unit was placed aboard the Atlantic Fleet flagship USS OMAHA (CL 4).

March 1938: Recording equipment was sent to Guam.

June 1938: Congress authorized $85,000 for improvement Radio Facilities at Corregidor, Philippines.

1939: The Naval Research Laboratory was working on two important tools for the RI community.  One of these was scrambled speech while the other was the development of a Radio Finger Printing (RFP) system.  The RFP was composed mainly of a camera equipped oscilloscope.  That summer the RFP equipment was transferred to Cavite for field testing against the Japanese.

January 1939:  In its annual report to DNC, on personnel availability, OP-20-G reported that there were 78 RI qualified operators on assignment.  Thirty six of these men were located with CINCAF: One aboard the flagship USS AUGUSTA, nine at Station A (Shanghai), twelve at Station B (Guam), and fourteen at Station C (Cavite).  Twenty four were serving in the Eastern Pacific: Fourteen at Station H (Heeia), seven at S (Astoria), two at Mare Island, and one with CINCUS.  Eighteen were working the Atlantic problem: seven with the Navy Department, six at W (Winter Harbor), one in San Juan, two with Station F (Squadron 40-T aboard USS OMAHA) and two were attending Radio Material school.  In addition there were eight in OTRG Class number 21.

April-June 1939:  The flagship USS OMAHA with Station F onboard, deployed into the Black Sea.  RI unit onboard was manned by CRM N. V. Lewis and RM2 G. M. Mathis along with two general service radiomen.

September 1939:  OP-20-G requested 120 reserve radiomen to be brought on active duty to meet the demands of a formalized National emergency.  Sixty-one were desired in the shortest possible time to man the new HFDF sites.

October 1939: OP-20-G received a new title.  Known as the Communication Security Group since 1935, and briefly (March to October 1939) as the Radio Intelligence Section, it was now to be called the Communications Security Section.

October 14, 1939: Mission at Cavite (Station “C”) began to move to Tunnel AFIRM.

January 1940: DNC informed on status of plans for setting up strategic HFDF stations on Midway, Johnston and Palmyra in case of emergency.

Summer 1940:  The process of enlarging RI facilities on Oahu was proceeding at a rapid pace.  A new basement vault was under construction at Pearl Harbor to house the unit.  Plans for a new radio station near Wahiawa were underway as a replacement for the poorly located HFDF sites at Lualualei and Heeia, Hawaii.

October 15, 1940: The Cavite site terminated intercept operations.  The next day operations at Corregidor commenced.  The only remnant left at Cavite was the HFDF unit.  About the same time, all of the military dependents throughout the CINCAF operating area were shipped to the United States.

September 11, 1940: Army and Navy Agreement of joint exploitation of PURPLE.

Fall 1940: Station F (Squadron 40T) onboard USS TRENTON in European waters was disestablished.

October 4, 1940: In a memorandum by Safford suggestion that the Shanghai RI unit should be closed and the people moved to Cavite/Corregidor.  Of particular interest was the safety of the RIP-6 RIP-13.  The RIP-13 or M-3 was a Japanese Diplomatic Code Machine (Army RED Machine) and RIP 6 was the instruction for its use.

December 1940: Station Able in Shanghai, China closed with its mission and personnel transferred to Station C.

December 1940: At the close of 1940, records indicate that OP-20-G had grown during the year to ninety personnel; twenty-three of whom were officers (eight reservists), twenty-five civilians, and forty-two enlisted. 1940 yielded the last three classes from the roof of the Navy Department Building, bringing to bear 115 qualified intercept operators employed in intercept duties.  Actually the final class convened in November 1940 and graduated in February 1941.  Not counted in this number were those without RI training but who operated HFDF equipment, working as crypts-clerks, or were in COMSEC billets.

January 1941: A group of four officers departed Washington D. C. en route to London.  They traveled onboard HMS King George V and later were transferred to HMS Neptune.  The team, composed of Maj. Abraham Sinkov, USA, Capt. Leo Rosen, USA, LT Robert H. Weeks, USN and LTjg Prescott J. Currier, USN, carried with them nearly the entire inventory of recovered Japanese cryptographic material, including PURPLE and RED machines along with recovered keys and gave it their British counterparts.  In return, the British provided the team with a Marconi-Adock HFDF system, and most important, some information about Germany’s ENIGMA machine, which was needed to tack Germane Wolf Pack submarines in the Atlantic.

May 1941:  CNO direct that 23 of the navigation DF stations be transferred to the U.S. Coast Guard.

Early 1941 – June 1942: CDR Joseph J. Rochefort assumes OIC of Station HYPO.

July 1941: CNO request further development of Medium Frequency (MF) fixed Adcock DF for strategic use.

Final Quarter 1941: OP-20-G reported that the entire personnel structure was 821.  Of this total, 593 were yeomen, and four were either photographers or printer.  Fifty-six were operating in the Atlantic sector, 447 in the CONUS, and the remaining 318 in the Pacific.  To add emphasis to these numbers, undergraduates from seven Women’s Colleges began cryptologic training for eventual inclusion into a newly organized WAVES or the expanding Civil Service.

December 4, 1941: Orders were issued by OPNAV to destroy all classified publications except for those essential for operations on Guam.

December 7, 1941: WWII in the Pacific begins.

Multiple sources