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. 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 lieutenant named Laurance F. Safford was assigned to expand OP-20-G’s domain to radio interception. He worked out of Room 2646, on the top floor of the Navy Department building in Washington, D.C..

In February 1942 two new sections were headed by John R. Redman (Communications Combat Intelligence section) and Joseph Wenger (Communications Cryptanalytical section; to handle decryption and translation). As Japanese advances in the Philippines, the possibility of an invasion of Hawaii, and the increasing demand for intelligence, OP-20-G undertook two courses of action:

In Summer 1942 the Navy went through the motions of perhaps co-locating with the Army’s SIS but Commander Joseph Wenger had picked out the “perfect new home” for the rapidly expanding OP-20-G and acquired a private girls’ school Mount Vernon College for Women for $800,000 (a fraction of what the buildings and grounds were worth). So on 7 February 1943 it opened at what was called the “Naval Communications Annex”, and staff moved in over the next two months.

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)

Information above excerpted from Wikipedia

The various designations for departments in Op-20-G can be a confusing tangle of acronyms which changed from month to month. I’ve been able to sort out the departments, at least as they were organized 14 April 1944 thanks to Walter Reiss, husband of former WAVE Bertha Boron, who received the following document from the National Archives and shared it with me.

Op-20-G’s Subdivision Order No. 69

14 April 1944

The cognizance and functions of the various departments and sections under Op-20-G, and the relationship between certain departments and sections, are as follows:

  • I – Assistant Director and Assistants
  • 20-G: Assistant Director of Naval Communications for Communications Intelligence
  • 20-G-1: Operation and Planning (Technical)
  • 20-G-10: General Assistant to 20-G-1
  • 20-G-20: General Assistant to Op-20-G for dediCated-administration
  • II-Operations Coordination and Planning Staff
  • GX (D/F and Intercept Facilities
  • The Staff includes the following members:
  • Officer in Charge, Fleet Radio Unit, Melbourne
  • Officer in Charge, Fleet Radio Unit, Pacific Area
  • G-30 – Pacific Theater
  • G-40 – Atlantic Theater
  • G-50 – Research
  • G-60 – Technical Services
  • G-70 – Clandestine
  • G-80 – Strategic Information Coordinator
  • GC – Communications
  • GD-A – Intercept Control
  • GD-P – Intercept Control
  • GH – Secretary of Staff
  • GI-A – Correlation and Dissemination (Atlantic)
  • GI-D – Correlation and Dissemination (Diplomatic)
  • GI-P – Correlation and Dissemination (Pacific)
  • GR – Personnel
  • GT-A – Traffic Analysis
  • GT-P – Traffic Analysis
  • GX – (See end of list).
  • GY-A – Cryptanalysis
  • GY-P – Cryptanalysis

14 April 1944


Subj: Cognizance and Function of Sections Under Op-20-G.

Ref: (a) U.S. Naval Communication Intelligence Organization.

  • 1. This Subdivision Order supersedes Op-20-G Subdivision Order No. 67, dated 14 February 1944.
  • 2. The cognizance and functions of the various departments and sections under Op-20-G, and the relationship between certain departments and sections, are as follows:
  • I – Assistant Director and Assistants.

    • 20-G: Assistant Director of Naval Communications for Communication Intelligence.
    • 20-G-1: Operation and Planning (Technical)
    • 20-G-10: General Assistant to 20-G-1.
    • 20-G-20: General Assistant to Op-20-G for dediCated-administratiion
  • II-Operations Coordination and Planning Staff.

    The Staff is composed of officers stationed at Washington, who are fitted by experience and training to assist in the planning of future operations of the Communication Intelligence organization. The assistants to the Assistant Director as well as the officers in charge of the Fleet Radio Units at Pearl Harbor and Melbourne are ex-officio members. The Planning Staff, as a whole, will function principally as a coordination group with advisory powers. Small committees will be designated to plan specific new projects.

    GX (D/F and Intercept Facilities) has solely staff duties in connection with the coordination of Communication Intelligence activities, and these will be listed herein.

  • GZ-A – Translation
  • GZ-P – Translation.
  • GX – D/F and Intercept Facilities.
  • III – The Washington unit.

    • A. dedicated-administrative Department

      • G-20 – Head of dediCated-administrative Department
      • GB – Secretariat
      • GQ – Supply
      • GR – Personnel Records, Training and Allocation
      • G-21 – Senior Wave Assistant
      • G-22 – First Lieutentant (also Fire Warden and Air Raid Warden
      • G-23 – Security Officer
      • G-24 – Assistant Security Officer and Assistant Fire and Air Raid Warden
      • G-25 – Morale
      • G-26 – Transportation
      • G-27 – Navy Department Liaison
    • B. Pacific Theater Department

      • G-30 – Head of Pacific Theater Department
      • GD-P – Intercept Control (Pacific)
      • GT-P – Traffic Analysis, D/F and RFP (Pacific)
      • GY-P – Cryptanalysis and Decryption (Pacific)
      • GZ-P – Translation and Code Recovery (Pacific)
      • GI-P – Correlation and Dissemination (Pacific)
    • C. Atlantic Theater Department

      • G-40 – Head of Atlantic Theater Department
      • GD-A – Intercept Control (Atlantic)
      • GT-A – Traffic Analysis D/F and RFP (Atlantic)
      • GY-A – Cryptanalysis and Decryption (Atlantic)
      • GZ-A – Translation (Atlantic)
      • GI-A – Correlation and Dissemination (Atlantic)
    • D. Research Department

      • G-50 – Head of Research Department
      • GE – Cryptanalytic Research
      • GJ – Radio Engineering and Research
      • GK – Mathematical and Physical Research
      • [ed. note: written in by hand:] GP – Statistical Personnel Pool
      • GM – Machine Research
      • GV – Foreign Language Research
    • E. Technical Services Department

      • G-60 – Head of Technical Services Department
      • GB – Secretariat (Technical)
      • GC – Rapid Communications
      • GL – Collateral Information
      • GS – Machine Processing
      • GW – Traffic Center
    • F. Clandestine Department

      • G-70 – Head of Clandestine Department
      • GU – Clandestine
    • G. Diplomatic Department

      • G-80 – Strategic Information Coordinator
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  • Inside You’ll Find…

    WHO worked during the war? Find the Personnel section. Also, Joseph R. Desch
    WHAT were their goals? By the Numbers. Also, The US Bombe
    WHY? History of the Bombe Project A contemporary account of the reasons and the plans for their project for the Director of Naval Communications, 1944.
    WHERE was the project: In Dayton, it was in Building 26. In Washington, it was housed at the Naval Communications Annex