6988th SS History from 6988th.org

"History is a very tricky thing. ... The past actually happened, but history is only what someone wrote down."

— A. Whitney Brown (1991)

"History is a very tricky thing. ... The past actually happened, but history is only what someone wrote down."

— A. Whitney Brown (1991)

Okay. Whitney Brown is a comedian (among other things), but the above words are quite true, especially as it applies to the 6988th Security Squadron ... or to all of USAFSS, for that matter.
   So. What did happen during those 20-odd years of the 6988th's existence? And how much of it was written down? One researcher interested in the history of the 6988th wrote, "there are bits and pieces ... so much of it was classified that good records weren't kept."
   To help things along, previously classified documents (many, top secret) have been released recently by the National Security Agency (NSA), Department of Defense (DoD) and other agencies, through declassification programs — although "cryptanalysis" and "SIGINT Product Records" are exempt from the program. Nonetheless, some of the released documents have degrees of relevance to the 6988th's history, and, as such, other "bits and pieces" from them were used as references to put a bit more meat on the lean skeleton, in spite of the fact that all the released documents still contain prodigious redactions.
    But none of those documents would mean much without the foundation that the chapter on the 6988th's history in Larry Tart's book "Freedom through Vigilance" provided. (See "Acknowledgments" at the end of this write-up.)
    I don't think anyone would argue, however, that the truly absorbing history (you know ... the good stuff) is still out there ... deep within the minds and hearts of our colleagues — the Silent Warriors who were assigned to the 6988th, even on temporary duty, and for whatever length of time, from the early 1950s through the early 1970s. Perhaps some of those stories, written or oral, may someday be a part of this modest write-up to help invigorate and sustain the largely unheralded history of the 6988th Security Squadron.

The Beginning

Johnson AB Gate
Johnson AB Gate "A" - mid '50s

The 6988th Security Squadron had its roots in the 1st Radio Squadron, Mobile (RSM) — a long-serving US Army unit based at Johnson Air Base, Japan — about 12 miles (19 km) northwest of Tokyo. The 1st RSM was one of four Army RSMs transferred to the Air Force Security Service (AFSS or USAFSS) from the Army Security Agency (ASA) in February 1949, less than four months after the birth of USAFSS.

The 1st RSM's mission was "to provide radio intelligence to the Air Force commander and to the theater commander by means of radio intercept, radio direction finding, traffic analysis and evaluation of enemy radio traffic, telegraph and voice". While still part of the Army, the 1st RSM had been performing COMINT (communications intelligence) and COMSEC (communications security) missions for the newly-formed Air Force, but were ground-based operations.

USAFSS began plans for its ARP (airborne reconnaissance program; also "... platform") within weeks after the command was activated, but it didn't receive approval from USAF Headquarters to proceed with those plans until August 1950. With ARP approval finalized, USAFSS created and activated the 6920th Security Group (SG) at Johnson Air Base which immediately assumed responsibility from the Army Security Agency, Pacific, for the intercept and processing of all ground communications of the North Korean Air Force.

RB-50G no. 47-157
One of the actual ACRPs (click to enlarge)

Within a few months, USAFSS HQ also assigned responsibility for airborne COMINT reconnaissance operations throughout the Far East to the 6920th SG.

RB-29A no. 44-62290 (click to enlarge)

Originally, USAFSS had hoped to use the C-47 as its recon platform, and they actually tested that aircraft as well as a C-54. But USAFSS eventually decided on the RB-50 (pictured, left) as its long-range airframe, but none was immediately available. Until a sufficient number of RB-50s could be identified and reconfigured as ARPs, just one B-29, serial number 44-62290 (pictured, right) was converted for use as a reconnaissance platform and sent to the Pacific for testing in early 1952.

The Dawn of Airborne COMINT Missions

On 18 April 1952, as the Korean War continued to rage, USAFSS flew its first reconnaissance test mission in the Pacific with the modified RB-29. The mission focused on intercepting North Korean and Soviet air-to-air and air-to-ground communications using VHF frequencies with emphasis on ground control intercept (GCI). Test missions continued throughout the Far East and Alaska for the next several months.

In September 1952, the RB-29 was sent to Europe for additional testing for several more months. The test programs in both Europe and the Far East were a resounding success, convincing Air Force officials of the feasibility and efficacy of airborne intercept. This in turn resulted in final approval for USAFSS to acquire ten RB-50s (five each in Europe and the Pacific) and to establish detachments in each of the two theaters to operate the program.

USAFSS formally dubbed their new venture "ACRP" (airborne communications [or COMINT] reconnaissance program [or platform]). The airplanes were to be configured with equipment designed to primarily record voice transmissions in the VHF/UHF frequency ranges but also included HF (High Frequency), DF (Direction Finding), and CW (continuous-wave or manual Morse code) capabilities.

Even though the RB-29 used in testing was a prototype (it was never intended to be more than an "experiment") USAFSS decided to put the RB-29 to good use until the RB-50s were equipped and available for service. The plane returned to the States following the tests in Europe and repaired, upgraded and outfitted for operational use as an operational COMINT ACRP in the Pacific area.

In early 1954, the newly-refurbished RB-29 arrived in Japan and was assigned to the storied 91st Strategic Reconnaissance Squadron (SRS), Yokota Air Base, Japan, just four miles south of Johnson Air Base. (As one of the best equipped photo reconnaissance units in the Air Force, with a fleet of RB-29s, RB-50s and a host of other aircraft, the 91st SRS had relocated to Japan from McGuire AFB, NJ, to provide reconnaissance and other support during the Korean War.

That March, the 6920th Security Group at Johnson AB sent eleven crewmembers (intercept operators and airborne maintenance men) on temporary duty (TDY) for 90 days to the 91st SRS "for the purpose of accomplishing a classified mission in connection with this headquarters." The crewmembers included nine Russian linguists, one Chinese linguist, and an ELINT (electronic intelligence) specialist/electronics maintenance technician. The temporary assignment eventually led to a permanent change of station (PCS) to Yokota AB for all eleven men, who were to become the nucleus of the first airborne contingent at Yokota Air Base.

After the crewmembers familiarized themselves with the renovated RB-29, USAFSS flew its very first operational intelligence reconnaissance mission on 18 April 1954. Regular classified ACRP missions continued to be flown — averaging about nine a month — for the next two years using just the one aircraft: #44-62290.

In late 1954, the 91st SRS, a unit of the Strategic Air Command (SAC) was redesignated the 6091st Reconnaissance Squadron under the Far East Air Force (now PACAF). (About the same time, the 91st SRS, in name, "moved" back to the States and was recreated under SAC.)

In August 1956, the first COMINT-configured RB-50 finally arrived at Yokota and flew its inaugural operational ACRP mission later that month. The National Security Agency's COMINT wrap-up report on this first reconnaissance flight characterized it as a "VHF intercept mission."

The remaining four ACRP RB-50s scheduled to go to the Pacific made their way to Yokota AB over the next several months. The five RB-50s to be put into service in the European Theater were ferried over to Rhein-Main Air Base, Germany, between December 1956 and November 1957.

Transition to C-130s

RC-130B-II Yokota AB (click to enlarge)

The RB-50 ACRP program was to last only a few years.

With COMINT collection becoming increasingly valuable against the growing "VHF problem", the National Security Agency's interest in the ACRP program also increased. (See sidebar on the relationship between NSA & USAFSS, below right.)

With newer communications technologies being developed, NSA recognized the importance of developing a more extensive airborne intercept system capable of monitoring these new communications systems. This led to a new program in which the new Lockheed C-130 would be used as the next generation collection platform. The C-130 could fly longer and higher, operate out of airports with shorter runways, had the interior space to accommodate ten intercept positions (compared to only five on the RB-50G), and, being new, had significantly fewer maintenance problems. The new platform would be designated "RC-130A-II" and outfitted with appropriately updated communications systems.

The first of seven new RC-130A-II ACRPs was sent to Europe in June 1958.

Just three months later, disaster struck. On 2 September 1958 Soviet fighters shot down an RC-130A-II, tail number 60528, on an active reconnaissance mission after it strayed off-course over Soviet Armenia. All crewmembers, including eleven USAFSS back-enders, were presumed killed. After initially denying the incident, the Soviets eventually returned the remains of the front-end crew, but the remaining personnel, all USAFSS crewmembers, were never officially accounted for.

One critical outcome of this tragedy was the realization of how indispensable it was to have a qualified Morse intercept operator on board an ACRP aircraft. 60528 took off that day on what was to be a routine ACRP mission minus a Morse intercept operator. At the time, having a Morse operator as part of the crew was not a requirement, mostly because no one apparently was able to foresee any relevance to the mission or grasp the importance of having a Morse intercept operator on board who could monitor and track a target country's radar tracking station(s) to learn where the adversary thought our ACRP was.

On the day of the shootdown, a Morse intercept operator at a USAFSS ground intercept station in Germany was actually monitoring a Soviet radar station that was tracking 60528. The Morse intercept operator realized that the ACRP had flown seriously off course and immediately notified his superiors, but there was no way to alert the aircraft in time to avert disaster.

In the aftermath of this catastrophe, USAFSS put the pieces together, and many significant procedural changes were implemented. One far-reaching outcome was USAFSS' recognition that an on-board mission intercept operator did, in fact, have a critical role keeping the plane and crew out of harm's way — a major revelation. Consequently, just a few weeks after the incident, USAFSS HQ made it mandatory that all future USAFSS ACRP mission crews worldwide would include a qualified airborne Morse intercept operator. If none was available, or if he was unable to perform his duties, the mission would be canceled or aborted.

The two USAFSS organizations at Johnson and Yokota Air Bases underwent several name changes and reorganizations through the years to keep pace with the ever-expanding presence of USAFSS in East Asia. One notable change took place on 1 October 1958 when the detachment at Yokota was redesignated "Operating Location 1, 6988th Security Flight" … a milestone, of sorts, as this was the first time the unit was given that particular numbered moniker which it proudly bore in some fashion for the next 14 years. Not too long after, the 6988th Security Flight was redesignated "Detachment (Det) 1, 6988th Radio Squadron Mobile".

In January 1959, the transition from the RB-50s in Europe to the new RC-130A-IIs was complete. The RB-50s stationed at Rhein-Main, Germany, were transferred to the 6091st Reconnaissance Squadron at Yokota AB, resulting in a total of nine RB-50 ACRP aircraft operating out of Yokota. RB-50 missions continued in the Far East until May 1961, when the first of what would eventually be 11 new RC-130B-IIs began arriving at Yokota AB.

By the fall of 1962, all 19 RC-130s in both Europe and the Far East were in place. The emphasis on intelligence collection continued to be on voice ground control intercept communications over VHF/UHF frequencies.

ACRP mission routes that were being staged out of Yokota were generally along the periphery of the Soviet Union, North Korea or China, making sure the aircraft stayed well back from what the target countries claimed were their respective borders. USAFSS wanted to ensure that the newly-revised procedural and operational changes (e.g., more exacting maintenance, more extensive training, and newer, more accurate on-board navigation equipment, etc.) would provide much greater assurance that another shootdown similar to the 1958 incident over Armenia would not occur.

Fortunately, the command never experienced another shootdown.

On 1 July 1963, all USAFSS "RSMs" worldwide became "Security Squadrons". Consequently, what was then the 6988th RSM at Yokota was redesignated the 6988th Security Squadron — the designation it retained until being inactivated in 1972.



"The Nation's experience in Vietnam will be debated for years to come. But no one should ever forget the countless acts of courage and bravery demonstrated not only by our Nation's war fighters, but also by the silent sentinels of the cryptologic service."

— NSA Anniversary Brochure
60 Years of Defending Our Nation

The 6988th Security Squadron was but one of the multi-award-winning USAFSS units at various locales throughout East and SE Asia. Each unit played formidable and critically important roles for over a decade in all corners of the region. Much still can't be written about the some specifics surrounding the more sensitive missions, including individual roles or responsibilities. But as the years pass, more and more is coming to light via the protracted declassification of some documents (more accurately, portions thereof) by the NSA, which is presently the sole organization tasked with making all decisions regarding the declassification of cryptographic materials.


"[A]s early as 1962 the North Vietnamese and Chinese had reached a joint decision to challenge the increased US support of the South Vietnamese." (1, 239)

In the spring and summer of 1960, a series of high-level meetings between political and military leaders from the DRV (Democratic Republic of Vietnam) and PRC (Peoples Republic of China) got the attention of NSA, who was anxious to learn more.

ASA and USAFSS had already established several ground sites in and around SE Asia, but the bulk of the traffic they were intercepting was on HF frequencies, and that, mostly Morse code. NSA believed that the SIGINT they were seeking would more likely come from voice communications in the VHF spectrum, and this would require airborne assets as the collection sources because the ground sites had difficulty intercepting traffic on VHF frequencies because of the restrictive line-of-sight properties of VHF.

The 6988th had been flying reconnaissance routes against China up and down its eastern border from the Yellow Sea to the South China Sea since mid-1961, shortly after the first RC-130B-II arrived at Yokota. But with events rapidly unfolding in North Vietnam and Southern China, the US intelligence community (IC) sought a more concentrated collection effort to gain as much information as possible surrounding these (and possibly future) events.

In late November, 1963, two RC-130B-IIs and back-end crews from the 6988th were sent from Yokota to Don Muang Airport (a joint civilian/military airport) in Bangkok, Thailand, on a 15-day "test" mission code-named QUEEN BEE CHARLIE. The missions were flown over north and east Thai airspace roughly every other day for about ten days, after which the planes and crews returned to Yokota.

In March 1964, in spite of the fact that the results of the QUEEN BEE CHARLIE missions were marginal, NSA was determined to learn more of what was going mostly in Southern China. As a result, a Yokota-based ACRP and a 25-man contingent (two back-end crews) from the 6988th were deployed to Don Muang Airport in Bangkok and were to fly missions every other day. The task was similar to the December missions: identify and monitor communications traffic connected with yet another high-level Communist conference the previous month (February) in Mengzi, China. But this time, the ACRP missions were now to be flown over the Gulf of Tonkin instead of over Thailand in hopes of getting more, and more valuable, COMINT.

The change in the orbits proved to be extremely beneficial. The missions were so successful, a plan was quickly put in place to enable ACRP missions to be flown every day in the Gulf of Tonkin instead of every other day. Consequently, in July 1964, an additional RC-130B-II with a back-end crew from the 6988th at Yokota was sent to Thailand, and a new program supplanting QUEEN BEE CHARLIE dubbed QUEEN BEE DELTA was introduced flying ACRP missions over the Gulf of Tonkin on a daily basis (the two planes and crews, still staging out of Bangkok, would fly alternate days).

The timing was fortuitous, for in the days immediately following the Gulf of Tonkin incident (2 & 4 August 1964), a flurry of even more high-level, cross-border meetings between China and North Vietnam were held in Beijing, Kunming and Hanoi. China's response was immediate. On 6 & 7 August 1964, 36 MiG-17s (some reports: MiG-15s & 17s) were flown from China to the newly-expanded and upgraded (to accommodate jet aircraft) Phuc Yen air base, 12 miles northwest of Hanoi. (Here's another good article about the Gulf of Tonkin incident.)

After the Gulf of Tonkin Resolution was passed, China — in addition to supplying North Vietnam, and in fear of a US invasion of North Vietnam — quickly amassed troops and air power in key areas in South China, notably along the North Vietnamese border and on Hainan Island.

And it was very likely not coincidental that on 16 October 1964 China successfully tested its first atomic bomb.

On 2 March 1965, on the order of President Johnson, the air war began aggressively with the daily bombing of targets in North Vietnam and along the Ho Chi Minh trail (most of which was in Laos) under the ROLLING THUNDER program. It was also the month that the first (combat) US Marines came ashore at Red Beach Two, on the northern outskirts of Da Nang (Marine "advisors" had been in South Vietnam since the late 1950s).

In response to ROLLING THUNDER, the North Vietnamese developed (with Russian and Chinese help) a surprisingly exhaustive and integrated air and sea defense system anchored by modern Soviet coastal, early warning, GCI, and target acquisition radar systems throughout the country. Integrated with this defense system was what became North Vietnam's first line of defense: a vast array of Soviet and Chinese anti-aircraft artillery (AAA) sites, mobile and fixed, numbering in the hundreds.

As a result, the North Vietnamese Army (or PAVN, People's Army of Vietnam) were frequently able to detect US air strikes early. They would then be able to position their pilots into tactical advantage and warn them of the approaching American fighter-bombers. The American command would have liked to be able to warn US strike aircraft of any MiG threat, but in many ways, this air war was uncharted territory, and no reliable, secure system had yet been developed to effect timely warnings.

Just one month into ROLLING THUNDER, a pivotal event highlighted the consequences of this intolerable plight.

On 4 April 1965 a flight of ROLLING THUNDER USAF F-105D fighter-bombers was sent on a mission to attack a bridge complex 75 miles south of Hanoi. Meanwhile, pair of MiG-17s was being vectored by North Vietnamese GCI directly to the area where two of the F-105s were awaiting their turn to attack. Both of the heavily-ladened F-105s were shot down, and one of the US search and rescue aircraft, an A-1H Skyraider (possibly providing air cover for one of the downed aircrews) was also shot down by anti-aircraft fire. The following day, USAF received evidence sufficient to confirm that the Skyraider pilot had died at the time of the incident. The US learned about a year later that one of the two F-105 pilots that were shot down was captured and held prisoner by the North Vietnamese until being released in 1973. The fate of the other F-105 pilot has never been confirmed, and his status remains MIA/KIA.

One of USAFSS' orbiting ACRP planes had acquired timely SIGINT around the time of the attack that would have been helpful, but the lack of secure communications equipment, coupled with convoluted procedural issues, resulted in a delay which prevented that information getting to the ROLLING THUNDER pilots on that mission on time. A review of the incident revealed that two warnings were eventually sent to the F-105s over the radio, but well after the aircraft were shot down.

The sense of urgency to develop a system that would take advantage of the potentially life-saving intelligence collected by the ACRP and other intercept sites was acute. Pacific Security Region (the headquarters for AFSS operations in Asia/Pacific) had already devised a "brevity code" that could have been used by the ACRP back-end crew to directly warn pilots in imminent danger, but it didn't pass COMSEC scrutiny and therefore could not be used.

"For every example of the proper use of tactical SIGINT, there was the opposite instance, where the source was either not believed or not used properly."

— NSA, Center for Cryptologic History

"American Cryptology during the
Cold War; 1945-1989 - Book II"

In late 1965, two additional RC-130B-II aircraft from the 6091st RS and back-end crews from 6988th were sent to Thailand, enabling two COMINT missions per day. With this increase in the number of missions, ACRP assets and resources at Yokota AB were being stretched very thin. One option was for NSA and USAFSS to reposition assets — at least temporarily. The Air Force agreed to send one Strategic Air Command (SAC) RC-135D, with a joint SAC/6985th SS back-end crew from Eielson AFB, Alaska, to go TDY to Yokota twice monthly. At that point, every little bit helped.

QUEEN BEE DELTA missions began staging out of Ubon ['oo-bahn] RTAFB (Royal Thai Air Force Base) instead of Bangkok in the late summer of 1965. Even though Ubon was over 300 miles (483 km) closer to Da Nang, staging missions out of Thailand was becoming increasingly inefficient, particularly in terms of processing and delivering critical, perishable intelligence to the end users in the shortest amount of time possible.

One solution was to relocate and stage QUEEN BEE DELTA missions from Da Nang AB. However, the Commander-in-chief, Pacific, ruled out any relocation because of a lack of sufficient maintenance, billeting facilities, and secure hardstand (parking) space. A partial solution was implemented a few months later when the Pacific Security Region Commander arranged to have all 6988th back-enders relocated to Da Nang AB, primarily to expedite SIGINT processing.

Not unexpectedly, the crewmembers bemoaned the move but actually adapted to their new environment from the comfy confines of their hotel in Bangkok and their near-nightly visits to nearby Dino's Bar (now closed) for a cold Singha ... and maybe some local conversation. Getting used to the warm beer at Da Nang was rough, but it didn't take long for the crews to figure out how to chill the beer in the back end of the C-130s.

The Air Force did make incremental changes to improve living conditions at Da Nang. They built barracks for the guys who were stationed there PCS, but the TDY folks were still housed in 20-man tents. But instead of being secured with wooden poles, rope and stakes, they were replaced by tents with a robust wooden frame, concrete floor, much better lighting, and screened-in sides. Cots gave way to bunk beds with thicker mattresses and newer mosquito nets (fewer holes). Later versions of the tents included an even more robust frame and roll-up outside bamboo curtains. Never got air conditioning, though. Outhouses were even eventually replaced with a real latrine and showers with running water (unheated). (See "Tent City" photos at Da Nang)

Moving the crewmembers to Da Nang resulted in a "split" operation where the 6091st would fly the an RC-130B-II from Thailand to Da Nang, stop just long enough to pick up a back-end crew, and proceed to the assigned orbit area. Upon mission completion, the planes would land at Da Nang, drop off crewmembers, post-mission processing material, and immediately take off and head back to Ubon.

Chinese-US Encounters

Recently released documents from the NSA (July 2014) indicate that there were at least eight (one source mentioned twenty) instances during the Vietnam War where the People's Republic of China (PRC) engaged — and in some cases, shot down — American jet fighter aircraft, but only when Chinese airspace was inadvertently violated by US fighter aircraft. One of those engagements has a strong connection to several former members of the 6988th.

Capt Smith
Captain Smith
c. early 1960s

On 20 September 1965, Captain Philip E. Smith, USAF, was flying a combat air patrol mission protecting a QUEEN BEE DELTA mission in his F-104 on an overcast day over the Gulf of Tonkin.

As a late substitution for another pilot, Smith took off from Da Nang without a wingman, but followed the routine of getting his tanks topped off from the airborne tanker and then requesting radar vectors to hook up with his flight to start his mission. Everything seemed to be going according to plan, but Smith was having difficulty making the hook-up in spite of his getting radar vectors (directional instructions) from the radar site (call sign "Panama") at Monkey Mountain near Da Nang. Other US pilots who could hear Smith also attempted to help him, but he was still unable to locate his flight. Puzzled as to what might be wrong, Smith was startled to discover that both his primary and backup on-board compasses had become inoperative, rendering the vectors he was getting from Panama useless. Smith now only had intermittent radio contact with Panama (sometimes via relays through other aircraft), but lacking any directional capability and out of range of any US navigational aid, he eventually fell off the radar screen and lost all radio contact.

Smith was lost and very likely getting farther away from where he needed to be. He was flying in clear skies, but with a carpet of solid white clouds below him, he was unable to get his bearings from any visual references. In an attempt to determine his location, with unfolded maps in his lap, Smith descended under the cloud cover and noticed a coastline but was unable to discern what coastline. Before Smith realized it was the coast of Hainan Island and had unwittingly penetrated Chinese airspace, he was suddenly but not totally unexpectedly intercepted and attacked from behind by a pair of Chinese Naval Air Force MiG-19s. (As noted in the declassified documents, a "SIGINT Review" showed that as many as ten Chinese fighters may have been scrambled in response to the incursion.)

Col Smith
Col Philip E Smith, USAF (Ret)

Smith attempted a counter-attack, but his jet was too severely crippled, and he was forced to eject. Smith splashed down a few hundred yards off the coast of Hainan Island in the middle of a fleet of Chinese fishing boats. He was picked up, turned over to authorities and immediately sent to Guangzhou ("Canton"), where he was detained, interrogated, and ultimately sent to a Beijing prison where he was held in solitary confinement for seven and a half years. In March of 1973 Smith (then a major*) was released along with three other Americans who were also held by the PRC in the same prison.

Smith — the only known USAF pilot to be held by the Chinese — was promoted to Lt Col one month after his return and decided to remain in the Air Force. Philip E Smith retired as a full colonel in June 1987 after 32½ years of service to his country.

*POWs and those who were listed as MIA were automatically promoted when eligible

Col Smith's story — his shootdown, capture and imprisonment — is well-chronicled in his riveting book "Journey Into Darkness," from which this episode was mainly summarized. [4]


Fearing the project name "Queen Bee" had been compromised as a result of the shootdown, the project name for all ACRP flights in Asia was changed to "SILVER DAWN". In February 1967 the project name was once again changed to the unclassified names "Commando Lance" for ACRP flights in SE Asia and "Commando Royal" in all other areas.

Meanwhile, USAFSS continued to experience serious manpower shortages, mostly linguists, in all of their units throughout the Far East — but especially in Vietnam. Virtually all back-enders from the 6988th SS (mostly Chinese Linguists and Morse operators) were going TDY to Da Nang non-stop on 28-30-day assignments with only a week or two, at most, in between trips. To help out, Vietnamese and Chinese linguists from the 6924th SS at Da Nang and from The Philippines were conscripted for flying duty even though they never had any formal airborne training.


General Klocko
Maj Gen Klocko, USAFSS Cmdr 1 Sep 62 - 15 Oct 65

The USAFSS commander, Major General Richard Klocko, in anticipation of the need for additional assets and capabilities to support the war effort, had long since begun the process of attempting to add RC-135s to the ACRP program. As early as 1964, General Klocko had submitted a request to the Air Force for six RC-135s to augment the 11 RC-130B-IIs that were on missions as often as possible from the northern tip of Hokkaido (Japan) to SE Asia.

The RC-135 already had established a proven track record as a reconnaissance platform for the Strategic Air Command (SAC), and USAFSS acutely needed more assets. Unfortunately, just a few months after the request was submitted, DoD rejected General Klocko's proposal.

On 14 October 1965, just two days before the General Klocko's tour as USAFSS commander was to come to an end, the Department of Defense — bolstered by recommendations from a Joint NSA/DIA Airborne Resource Study — agreed to add the six RC-135s to the airborne effort in the Far East. The plan was to have the 6988th SS initially provide the back-enders for the RC-135s, and the aircraft would be assigned to and flown by front-enders from SAC.

Although the initial plan was reportedly to base the six RC-135s at Yokota AB, the final decision on where they should be "permanently" based became a point of contention. Under consideration were Japan, Thailand, The Philippines, Da Nang, and Okinawa. In true government fashion, it wouldn't be for another 18 months that a base of operations for the RC-135s was selected.

The fall of 1965 ushered in a new threat in North Vietnam — the appearance of Russian SA-2 surface-to-air missiles (SAMs). Multiple instances of newly-acquired COMINT from ACRP missions confirmed that Russian and Chinese military personnel were controlling SAM launches against US strike aircraft.

To counter the SAMs, 7th Air Force (7 AF) introduced a procedure in which SAM activations acquired by an ACRP would be passed to 7 AF through the 6924th SS (the USAFSS unit at Da Nang), which would in turn direct SAM suppression missions against the offending SAM site/s. ACRP aircraft also had the ability to warn US forward air controllers of impending or suspected hostile North Vietnam Air Force activity. Unfortunately, this was not always possible.

While the ACRP often had the information pilots needed to avoid areas of active SAM activity, to avoid being shot down, or to do some shooting down themselves (e.g., the ROLLING THUNDER incident) the ongoing problems of security and other procedural restrictions prevented its use.

Thirteen months after the ROLLING THUNDER incident, an international incident forced much needed changes to the cumbersome and oft-ineffective warning system. This event also underscored what came to be known as "the Pearl Harbor question": If SIGINT were available, why wasn't it used?

On 8 May 1966, a flight of RB-66s escorted by F-4Cs over North Vietnam unwittingly strayed over the ragged border into Chinese airspace. The Chinese scrambled four MiG-17s to intercept the wayward flight. A dogfight ensued, and one of the MiGs was shot down (the only casualty) crashing seventeen miles inside Chinese territory. The incident elicited a strong diplomatic protest from Beijing which included threats to widen the war. The US Air Force claimed that the fighters never strayed over the border. However, the PRC released photos of the downed MIG and of the F-4s' jettisoned auxiliary fuel tanks 17 miles inside Chinese territory. Moreover, a subsequent SIGINT review (including Morse code tracking) indicated that there was an intrusion.

The offending American pilots should have been warned they were on a course that would take them over China. The collection or interpretation of the telltale SIGINT wasn't the issue. Rather, the problem was in the process of getting the intelligence to the pilots so they could act on it. In this instance, seven messages from the SIGINT center at the 6924th SS at Da Nang to the Control and Reporting Post (CRP — located at Tan Son Nhut at the time) warning of the impending border crossing were, in fact, sent. The CRP tried to relay the messages to the Navy's "BIG LOOK" EC-121 that was supposed to act as a communications relay to the offending flight, but the BIG LOOK mission had either aborted or was never launched. The CRP also supposedly tried to pass the warnings via the USN's communications and control ship on station in the Gulf of Tonkin, but no one could confirm that the warnings had ever been sent. Either way, the warnings from Monkey Mountain never had a chance of getting to the F-4C or RB-66 pilots.

Fueled by PRC's ire, and to avoid a similar recurrence, this critically sensitive incident led to a full-scale Pentagon investigation — and the eventual streamlining — of command, control and communications procedures throughout SE Asia.

Three of the major procedural changes were: (1) ACRPs were brought into the warning system with communications gear that could relay the MiG alerts and border encroachment warnings. (2) BIG LOOK flights were put under 7 AF's control so that there was an assurance they would be in orbit when strike missions were flown. (3) The new Tactical Air Control Center - North Sector was established at Monkey Mountain adjacent to the USAFSS facility, manned with SIGINT-cleared personnel, and assumed complete control of air combat operations over North Vietnam.


By mid-1966, both the infrastructure and security at Da Nang AB (even though it had justifiably garnered the nickname "Rocket City") had expanded and improved to the point that it was deemed "safe" to base the RC-130B-IIs at Da Nang, so the aircraft and the 6091st crews & maintenance personnel relocated from Ubon AB, Thailand, to Da Nang AB.

That lasted about a year.

Around midnight, 15 July 1967, there was a devastating rocket attack on Da Nang by the Viet Cong (VC) that destroyed ten or eleven aircraft (accounts differ) and damaged dozens more. (Click here to watch a news video of the attack.)

Fortunately, the RC-130B-IIs escaped unscathed, but the severity of the attack and the fear of similar attacks in the future brought a quick end to having the ACRP aircraft based at Da Nang. Four days later, the planes, the front-end aircrews and the support group were once again moved — this time to Cam Ranh Bay, 350 miles (563 Km) south. Crewmembers on TDY from the 6988th remained at Da Nang.

Dawn of a New Era

RC-135M - Kadena AB - May 1972
(click to enlarge)

Finally, in early 1967, the debate over where to base the six RC-135 ACRPs was resolved: the site chosen was Kadena Air Base, Okinawa.

On 15 July 1967 USAFSS activated the 6990th Security Squadron at Kadena AB, and the following month, a core group of linguists, Morse intercept operators, and airborne maintenance technicians from the 6988th SS in Yokota permanently transferred to the 6990th. One month later, SAC activated the 82d Strategic Reconnaissance Squadron initially at Yokota AB, moving to Kadena AB in January 1968, to operate and maintain the RC-135s.

Four of the six RC-135s were actually delivered to Yokota AB starting in May 1967, apparently for training and familiarization purposes, as the first official operational mission wouldn't take place until that September. The remaining two 135s were sent directly to Kadena, the first on 10 September 1967. By November, the RC-135s at Yokota had moved to Kadena.

With the USAFSS & SAC units activated, and the aircraft in place, the 6988th SS began to turn over responsibility for COMINT reconnaissance missions in SE Asia to the 6990th Security Squadron.

On 12 September 1967 the 6990th SS flew its first operational mission just two days after the first RC-135 arrived at Kadena. By November, the squadron was flying scheduled missions on a daily basis.

"Officially," the 6988th Security Squadron flew its last RC-130B-II mission in the Gulf of Tonkin on 31 December 1967, and, on 1 January 1968, the 6990th SS (again, "officially") assumed responsibility for manning the back-end crews for both the RC-135s (project name: "Combat Apple") and the Commando Lance (RC-130B-II) missions, which were still being staged out of Cam Ranh Bay — until the program ended in 1971. The 6988th SS would still send back-enders TDY to Kadena, Cam Ranh Bay or other outposts as necessary.

Earlier in 1968, the 6091st Reconnaissance Squadron was redesignated the 556th RS. There was no change in the personnel, aircraft or missions.

The back-enders who remained assigned to the 6988th started to settle in to their routine of four years earlier — flying daily "round-robin" reconnaissance flights in NE Asia out of Yokota — but, alas, that "routine" was very short-lived.

Hold Everything

USS Pueblo in Pyongyang N. Korea
USS Pueblo on display in Pyongyang, the capital of North Korea. The Pueblo was spruced up inside and out in 2013 in honor of the 60th anniversary of "Victory Day" (of course they claim to have won the Korean War). Tours available, just fyi, the next time you're in North Korea. (click to enlarge)

On 23 January 1968, the USS Pueblo, a Navy SIGINT collection ship on its maiden voyage, was attacked and seized by the North Korean Navy in international waters 25 Km (15.5 miles) off the coast of North Korea. One US seaman was killed, and the 82 other crewmen were captured and imprisoned for 11 months.

The operational impact on the 6988th and other USAFSS units in both Japan and South Korea was immediate. USAFSS ordered the rapid deployment of two aircraft and about 30 crewmembers from the 6988th to Osan Air Base, South Korea.

On 28 December 1968, the detained crew of The Pueblo was released. The ship, however, has remained in the hands of the North Koreans to this day (see photo at right).

Another Unprovoked Catastrophe

Military aggression by North Korea against the US tragically struck again on 15 April 1969 when an unarmed US Navy EC-121 ACRP, tail number PR-21 (see photo below left) staged out of Naval Air Station Atsugi, Japan, was shot down by two North Korean MIG-21s over international waters. All 31 crewmembers perished.

USN EC-121 PR-21
US Navy EC-121 PR-21 (click to enlarge)

After a short stand-down, USAFSS and Navy reconnaissance flights resumed, but now under the protection of fighter escorts. With tensions between the US and North Korea at an all time high, the number of sorties from Osan AB increased to three nine-hour missions per day with 24/7 coverage. All branches of the service were now pumping out Korean linguists as fast as possible from the Defense Language Institute as well as recruiting native speakers who could qualify for security clearances.

The heavy reconnaissance activity targeting North Korea was not limited to Osan AB. The 6988th at Yokota was sending back-end crewmembers TDY to Itazuke AB, Japan, to crew the Air Force EC-121s that were also flying three reconnaissance sorties a day against North Korea, mirroring the RC-130B-II operations. This high level of activity necessitated a dedicated support unit, so USAFSS activated Operating Location 2, 6988th SS (or OL2 — also known as OL-EA) at Itazuke Air Base to support the TDY crews from the 88th.

By the end of 1971, tensions had eased between the US and North Korea to the point that USAFSS was able to reduce the number of missions from both Osan and Itazuke to two per day, seven days a week, eventually tapering off to just one mission a day, five days a week, Monday-Friday.

Because of the fewer number of missions, USAF EC-121 operations at Itazuke AB were relocated to Kwangju Air Base, South Korea. 6988th ACRP crews ended three years of TDY operations at Osan Air Base, and missions against North Korean targets were staged out of Yokota.

However, that didn't quite work out. Due to the long flight times between Yokota AB and the target areas, the time needed to be near or "on station" to meet intelligence collection objectives was insufficient. As a result, ACRP missions staging out of South Korea were revived — this time from Suwon Air Base, South Korea. Back-enders from the 6988th were once again sent packing TDY to South Korea to crew those missions.

All Good Things Must Come to an End

Early in 1972, with American participation in the Vietnam War winding down, a DoD budget-driven decision forced a complete realignment of the cryptologic structure in Japan. As a result, three USAFSS units in Japan were to be shut down, including the 6988th SS at Yokota. All USAF EC-121 operations were discontinued, and the tasking for all remaining RC-130B-II ACRP missions was transferred to the 6903rd SS at Osan AB, South Korea. All remaining USAFSS personnel at Yokota were reassigned to other units within the command, with most getting orders to transfer PCS to the new 6990th Security Squadron, Kadena AB, Okinawa.

An historic and illustrious era in SIGINT activity in East and Southeast Asia had drawn to a close.

On 30 June 1972, USAFSS officially folded the flag of the 6988th Security Squadron.



Following the inactivation of the 6988th, nine of the RC-130B-IIs were transferred to the 7406th Support Squadron at Rhein-Main AB, Germany, to replace the aging RC-130A-II models. Most of those RC-130B-IIs continued in service as SIGINT ACRPs for two more years, then were "de-configured" as ACRPs and reconfigured as regular cargo C-130Bs.

In name, the 6988th Security Squadron was to live another day — however temporarily — at the opposite side of the globe. On 1 June 1980, Major General Doyle Larson, commander of the Electronic Security Command (the immediate successor to USAFSS) redesignated the 6954th ESS (Electronic Security Squadron) at RAF (Royal Air Force) Mildenhall, United Kingdom, as the 6988th ESS in honor of the venerable, illustrious (etc., etc.) organization that had its home at Yokota Air Base, Japan, but operated out of more than a dozen locations throughout the Asia Pacific region for over 20 years.

On October 1st, 1993, the "6988th" moniker was once again retired — very likely, permanently — as the 6988th ESS at RAF Mildenhall was redesignated the 488th Intelligence Squadron as part of the what was the newly minted and restructured Air Intelligence Agency (AIA) — the third in a line of six successor organizations to the pioneering grandfather of them all, the inimitable, and to most if not all of us, never-to-be-forgotten, United States Air Force Security Service.


Notes (working)

  1. Hanyok, Robert J. (2002). Spartans in Darkness: American SIGINT and the Indochina War, 1945–1975. United States Cryptologic History, Series 6, NSA Period: 1952–Present, Vol. 7. Fort Meade, MD: Center for Cryptologic History, National Security Agency. 239.
  2. Vietnam: A SIGINT Paradox (Part I) (1998). Cryptologic Almanac 50th Anniversary Series.
  3. Xiaoming Zhang (1996). "The Vietnam War, 1964-1969: A Chinese Perspective." Journal of Military History, 60. 734-741.
  4. Smith, Philip E. & Herz, Peggy (1992). Journey into Darkness. New York, NY: Simon & Schuster, Inc.