By March 1962, the 3rd RRU had evaluated the marines’ performance and reported back to Director National Security Agency (DIRNSA).

The ASA suggested that if the marines were to be extended past their initial 120-day mission, their site should be moved to the Danang area and be assigned a mission in support of the effort by the army intercept site in the Philippines. It was determined that the Marine Corps effort at Pleiku mostly duplicated that of Army’s at Phu Bai. Furthermore, it was noted that the resulting intercept was below the standards of Bien Hoa in terms of quantity and quality.

Late in 1963, the marines shifted their base from the mountainous Central Highlands at Pleiku to the newly established station at Phu Bai near Hue where they moved in with the ASA. There they worked with ASA personnel who trained the marines in traffic analysis (TIA) and intercept of communist communications. As the marine expertise grew, the detachment took on new missions with emphasis on the Democratic Republic of Vietnam (DRV) naval communications, including Hanoi’s coastal surveillance radar network and the tactical command and control of its small navy of patrol craft and torpedo boats. Eventually, marine operators would work with the expanding Air Radio Direction Finding (ARDF) program and the KIT KAT SIGINT support project for OPLt\N 34A missions.

The mission of training in a live environment proved its worth in 1965 when Marine Corps combat units arrived in the region. The marine SIGINT contingents in the area were able to immediately provide support for the large marine force as it settled in the northern I Corps Tactical Zone (CTZ). One small element [ — ] would set up an intercept site at a small village nestled in the hills of furthermost northwest Vietnam that would be significant for the marines in 1967 to 1968 – Khe Sanh.

Unlike the marines (and their Naval Security Group commanders), who approached Vietnam on a tactical scale, made few long term plans, and spoke only of committing support detachments, the Air Force Security Service approached the situation in Southeast Asia with a strategic plan in mind. [ — ] Southeast Asia, then, was seen most importantly as a platform for cryptologic operations, whether by direct Air Force special security (AFSS) presence or through the help of other countries, [ — ]

In fact, by May 1960 the AFSS had a contingency plan already developed which spelled out the various measures to meet SIGINT requirements in the re ion. The senior AFSS echelon in the Pacific, [ — ] had written up an operational plan for a mobile contingency capability in Southeast Asia. The  [ — ] established a COMINT Contingency Unit (CCU),which consisted of unmanned mobile vans, at Clark AFB, Philippines, designated the 6922th Radio Group Mobile (RGM). The unit was supposed to provide a capability to intercept and process communications intelligence in locations not presently occupied by subunits [ — ].    The personnel to man the prepositioned vans were to be drawn from the Pacific theater or U.S. mainland sources. The plan was coordinated within the framework of existing Pacific Air Force (PACAF) crisis planning for the western Pacific. Since possible air force deployments were tied to existing airfields in the region which could accommodate U.S. aircraft, the actual deployment sites were Limited to [ — ] and Tan Son Nhut, South Vietnam.

Featured image: 3rd RRU intercept operators

Source: Spartans in darkness: American SIGINT and the Indochina War, 1945-1975