NSA AND SOG
I was in the ASA [Army Security Agency], but not in Vietnam. We were the Army's NSA unit. There was indeed a strong relationship between the ASA/NSA and SOG -- especially during the last 3 years of the Vietnam War.
One of the projects that I and many other SOG and ASA types [including Robert Noe] have been researching (since early 2009) is the EXPLORER project. The SOG/SF lead Bru Montagnard Security Platoons protected some of the bases where the EXPLORER was located -- often in enemy controlled "denied territory." One of the EXPLORERs was "across the fence" in Laos at a base called Leghorn (aka Golf 5).
The EXPLORER was one of the most carefully guarded secrets of the Vietnam War. It was a complex of remotely-conrolled VHF intercept receivers and radio relays that collected the tactical communications of the NVA. The intercepts were transmitted to remote ASA field stations where they were translated and analyzed. The equipment was all custom, state-of-the-art, solid state; the project was classified TS Crypto, which is one of the reasons SOG was chosen to protect and maintain the remote outposts. The first EXPLORER was installed on RR Hickory in Quang Tri Province. It was operational in Aug of 1970. Hickory was overrun in early June 1971. Other EXPLORERs were installed at FSB Sarge, Alpha 4, and (as mentioned) Leghorn. There is an account of the loss of Hickory and the (unmentioned) EXPLORER in John Plaster's book "SOG."
The relationship between SOG and the ASA/NSA was really on a "as-needed" basis. There was no "formal" structured relationship. They were completely different organizations with their own chains of command, different training, unit structure, etc.
Both were volunteer organizations. Virtually all of the SOG personnel were SF qualified. Likewise, the NSA, ASA, Naval Security Group (NSG), US Air Force Security Service (USAFSS) were highly trained, highly qualified, selected "volunteers." Both organizations required their personnel to obtain Top Secret security clearances, which entailed a thorough background investigation (BI). When positioned "outside of the the wire" in combat zones, both units typically wore "sanitized" uniforms or operated undercover. Some ASA/NSA personnel were forbidden from leaving protected bases and compounds. Many of them did anyway.
Unlike SOG, ASA/NSA personnel were typically (but not always) "rear echelon" personnel -- linguists, traffic analysts, intercept operators, and other specialists. There were a few ASA units that were collocated with combat units in hazardous outposts. The 265th (ASA) RRC (Airborne) served with the 101st Airborne in some of the bloodiest battles of the Vietnam War. ASA personnel were often stationed at forward, remote outposts, which were overrun. The last two ASA personnel killed in Vietnam were stationed at FSB Sarge, where an EXPLORER was located. That base, like RR Hickory and Alpha 4, was overrun. There was a small ASA detachment in Quang Tri that supported ASA personnel operating near the DMZ. There was one ASA unit that was SF qualified -- the 400th USASA SOD (Special Operations Detachment).
If you Google SOG you'll find several nonfiction works -- in addition to those of John Plaster. If you're interested in the NSA/ASA during the Vietnam War era, I highly recommend Douglas Bonnot's "The Sentinel and the Shooter." You may want to read James Bamford's "Body of Secrets" and "The Puzzle Palace" which will give you a good understanding of the NSA and its missions. The "official" history of the ASA in Vietnam was authored by James Gilbert (INSCOM historian) -- "The Most Secret War" -- in which he briefly discusses the EXPLORER but does not mention SOG. Regarding the 400th USASA SOD, you may want to read John E. Malone's "Top Secret Missions" which is the history of his unit.
Much has been written about SOG personnel. Plaster's books are some of the best.
Again, the relationship between SOG and the ASA/NSA was tenuous and transitory. It was informal and based on the necessities of a few specific missions -- the EXPLORER project was one of them.
Louis T. Girdler