The Secret Sentry (18 page)

And army and marine field commanders at the corps and division levels who did have access to SIGINT failed to use it properly.
Many had little or no knowledge of, or prior experience with, SIGINT and therefore were suspicious of a source that they did
not control, much less understand. The list of senior army commanders who went to Vietnam knowing next to nothing about SIGINT
is staggering. General Creighton Abrams Jr. admitted, “It has been my feeling in years past that we did not know too much
about ASA [Army Security Agency].” The military services were largely to blame for failing to educate their senior officers
in the fundamentals of this vitally important battlefield intelligence source, especially given how crucial SIGINT had proved
to be during the Korean War. But NSA also bears a large part of the blame because of the agency’s insistence that all aspects
of SIGINT “sources and methods” be kept a secret from all but those few officers deemed to have a need to know.
²⁹

The Tet Offensive

Back at NSA’s Indochina Office (B6) at Fort Meade, while the Battle of Dak To was raging and the Vinh Window was just opening
up, a number of disturbing signs were beginning to appear in intercepts arriving via teletype from Southeast Asia. Beginning
in late October 1967 and continuing through November, SIGINT detected elements of two crack North Vietnamese divisions, the
304th and the 320th, and three indepen dent regiments departing their home bases in North Vietnam and moving onto the Ho Chi
Minh Trail in southern Laos. This was the first time ever that NSA analysts had seen two North Vietnamese divisions moving
onto the trail at the same time. By mid-December, the troops had been tracked by SIGINT to staging areas around the southern
Laos city of Tchepone, just across the border from the U.S. Marine Corps firebase at Khe Sanh.
³⁰

Then during the first week of January 1968, radio transmitters belonging to two regiments of a third North Vietnamese division,
the 325C, were detected operating north and west of Khe Sanh. At the same time, SIGINT monitored the first two divisions surging
across the border into South Vietnam and taking up positions south and east of the firebase. The marines inside the base were
now surrounded by vastly superior enemy forces. Everyone from President Johnson down to General Westmoreland in Saigon immediately
assumed that the North Vietnamese were about to launch a major offensive to take the base.
³¹

But the ominous portents continued to build in the days that followed. By mid-January, SIGINT showed that there were three
NVA division headquarters and at least seven regiments totaling more than fifteen thousand enemy troops deployed around the
Marine Corps firebase. To the south of Khe Sanh, in the Central Highlands, an accumulation of intercepted radio traffic passing
between the North Vietnamese B-3 Front headquarters and its subordinate divisions indicated that the North Vietnamese were
preparing to attack a number of cities in Kontum, Pleiku, and Darlac Provinces. To the east along the coast, SIGINT detected
the North Vietnamese Second Division moving southeast to staging positions outside the city of Hué, the largest urban center
in northern South Vietnam. Within a matter of days, the huge NSA listening post at Phu Bai was monitoring North Vietnamese
and Viet Cong radio transmissions coming from just outside Hué itself. Phu Bai and NSA’s other listening posts in South Vietnam
detected a dramatic increase in the volume of radio traffic passing along critical North Vietnamese and Viet Cong communications
links throughout South Vietnam, much of it high-precedence messages. Unfortunately, NSA could not read the codes the messages
were enciphered with. On January 17, NSA issued an intelligence report warning that there was now firm evidence that the North
Vietnamese were preparing to launch an offensive in Pleiku Province, in the Central Highlands.
³²
Westmoreland and the U.S. embassy in Saigon interpreted this as an indication that the offensive would target the Central
Highlands and Khe Sanh, just south of the DMZ, an opinion shared by President Johnson and his senior advisers. But at this
stage, there were no reliable indications whatsoever coming from SIGINT or any other intelligence source to suggest that the
North Vietnamese and Viet Cong intended to mount any offensive operation south of the highlands.
³³

The suspicions of the White House and Westmoreland about the enemy’s intentions were apparently confirmed when on January
21 three battalions of the North Vietnamese 325C Division launched a two-pronged assault on marine defensive positions to
the north and south of the besieged Khe Sanh firebase. The North Vietnamese overran the village of Khe Sanh itself, but the
attacks on the base were repulsed. In response, a marine battalion was hastily flown in along with much-needed supplies, bringing
the size of the marine garrison to over six thousand combat troops.

But at the same time that NSA was reporting on the North Vietnamese military buildup in northern South Vietnam and the Central
Highlands, SIGINT collected in dependently by the radio intercept units belonging to the ASA’s 303rd Radio Research Battalion
at Long Binh, outside Saigon, revealed a dramatic surge in the number of Viet Cong radio transmissions coming from the area
surrounding Saigon, with many of the transmissions originating closer to Saigon than heretofore had been noted. By January
15, army intelligence analysts had concluded that three North Vietnamese and Viet Cong divisions, which had previously been
noted in Cambodia in late December 1967, were now confirmed by SIGINT as being deployed in an arc around Saigon within easy
striking distance of the South Vietnamese capital.
³⁴

During the ten-day period between January 15 and January 25, NSA listening posts in Southeast Asia intercepted what is described
in a declassified report as an “almost unprecedented volume of urgent messages . . . passing among major [enemy] commands.”
There were other equally troubling portents appearing in intercepts of low-level North Vietnamese radio traffic. North Vietnamese
units throughout South Vietnam were changing en masse their radio frequencies and cryptographic systems, activating forward
command posts and emergency radio nets, and North Vietnamese intelligence teams were detected in SIGINT reconnoitering target
areas
throughout
South Vietnam. The possibility of a major enemy offensive in South Vietnam had now become a probability. An internal NSA history
notes, “Never before had the indicators been so ubiquitous and unmistakable. A storm was about to break over South Vietnam.”
³⁵

On January 25, NSA sent a report to MACV titled
Coordinated Vietnamese
Communist Offensive Evidenced in South Vietnam
, the lead conclusion of which was this:

During the past week, SIGINT has provided evidence of a coordinated attack to occur in the near future in several areas of
South Vietnam. While the bulk of SIGINT evidence indicates the most critical areas to be in the northern half of the country,
there is some additional evidence that Communist units in Nam Bo [the southern half of South Vietnam] may also be involved.
The major target areas of enemy offensive operations include the Western Highlands, the coast provinces of Military Region
(MR) 5, and the Khe Sanh and Hue areas.
³⁶

Thanks to newly declassified documents, we now know that NSA’s warning message was either ignored, misunderstood, or misapplied
by the White House, the CIA, and MACV. The crux of the problem was that senior officials at MACV, in General Bruce Palmer’s
opinion as expressed in a later declassified CIA study, “flatly did not believe that the enemy had either the strength or
the command and control capability to launch a nationwide coordinated offensive.” George Carver Jr., the CIA’s special adviser
for Vietnamese affairs, also refused to accept warnings from his junior analysts because, according to the study, he “did
not fully buy the thesis that the coming offensive would be an all-out affair of great portent.”
³⁷
The January 28, 1968, edition of the CIA’s
Central Intelligence
Bulletin
commented, “It is not yet possible to determine if the enemy is indeed planning an all-out, country-wide offensive during,
or just following, the Tet holiday period.”
³⁸

General Westmoreland told Washington he was convinced that NSA’s intelligence about possible widespread attacks merely reflected
a North Vietnamese attempt to divert his attention from the real objective—Khe Sanh. Ultimately, however, the North Vietnamesenever
mounted a major attack on Khe Sanh coinciding with the launch of the Tet Offensive.
³⁹

In the days that followed, NSA intercept sites in Southeast Asia continued to pick up further “hard” indications that the
North Vietnamese offensive was about to be unleashed, including one intercept on January 28, which revealed that “N-day” for
the kickoff of the North Vietnamese offensive in the Central Highlands was going to be January 30, at three a.m., less than
forty-eight hours away. This report was deemed to be so important that it went straight to President Johnson.
⁴⁰

But the Defense Intelligence Agency believed that the North Vietnamese and Viet Cong would wait until after the end of the
Tet holiday to launch their offensive. So DIA too discounted NSA’s warnings, and its analysts wrote in the January 29, 1968,
daily DIA summary, “Indications point to N-Day being scheduled in the Tet period,
but it still seems likely that the Communists would
wait until after the holiday to carry out a plan
” (italics added).
⁴¹

Then, on the night of January 29–30, a U.S. Army SIGINT specialist named David Parks and his partner were manning a radio
direction-finding post at Bien Hoa air base, outside Saigon, just as the Tet holiday began. Parks later recounted, “About
midnight, every VC/NVA radio in the country went silent, ‘Nil More Heard’ for sure! We could not raise a ditty bop for love
nor money. It was the damnedest thing I ever
didn’t
hear. Complete radio silence.”
⁴²

Three hours later, at three a.m. on January 30, 1968, over one hundred thousand North Vietnamese and Viet Cong troops launched
a massive and coordinated offensive against virtually all cities, towns, and major military bases throughout South Vietnam,
attacking thirty-eight of the country’s forty-four provincial capitals and seventy district capitals, capturing the city of
Hué, seizing large portions of Saigon, and even managing briefly to seize portions of the American embassy in downtown Saigon.

Postmortem on Tet

After a month of unrelenting seesaw fighting, the Tet Offensive finally concluded by the end of February 1968. From a purely
militarystandpoint, the Tet Offensive turned out to be a clear-cut victory for the United States. The North Vietnamese and
Viet Cong lost an estimated thirty thousand troops in the battle. The enemy forces in South Vietnam were badly battered, with
SIGINT picking up signs of demoralization in the ranks of the North Vietnamese Army. According to General Daniel Graham, then
an intelligence officer in Saigon, “We could read the communications along the Ho Chi Minh Trail, and it was perfectly obvious
that they were having one terrible time because people from South Vietnam were going to go back up that trail come hell or
high water. All discipline had broken down and they were going back up the trail. Even some of the people who were operating
the radio stations along the trail had bugged out.”
⁴³

But while Tet may have been a military victory, it produced a political firestorm back in the United States. It shattered
American political resolve and devastated the Johnson administration. From a politicalstandpoint, Tet was an unequivocal strategic
victory for North Vietnam and the turning point in the Vietnam War—the defining moment when the U.S. government and the American
populace finally decided that they could not win the bloody conflict in Southeast Asia and that it was time to leave. On March
31, 1968, only two months after the beginning of the Tet Offensive, Lyndon Johnson went on national television and told his
fellow countrymen that he had decided not to run for reelection. This signaled the beginning of the end of America’s involvement
in the Vietnam War.

Not surprisingly, the postmortem reviews of the U.S. intelligence community’s per formance prior to the Tet Offensive praised
NSA. A CIA study states unequivocally, “The National Security Agency stood alone in issuing the kinds of warnings the U.S.
Intelligence Community was designed to provide.”
⁴⁴
A declassified Top Secret Codeword report submitted to the President’s Foreign Intelligence Advisory Board notes,

Despite enemy security mea sures, communications intelligence was able to provide clear warning that attacks, probably on
a larger scale than ever before, were in the offing . . . These messages, taken with such nontextual indicators as increased
message volumes and radio direction-finding, served both to validate information from other sources in the hand of local authorities
and to provide warning to sen-ior officials. The indicators, however, were not sufficient to predict the exact timing of the
attack.
⁴⁵

But recently declassified material reveals that prior to the launch of the Tet Offensive, NSA only had definitive information
that indicated imminent North Vietnamese and/or Viet Cong attacks in eight South Vietnamese provinces, all in the northern
part of the country or in the Central Highlands. The provinces around Saigon and the Mekong Delta were never mentioned in
any of the NSA reports. Except for the January 25 message detailed above, the NSA intelligence reporting provided no indication
of the enemy’s intent to undertake a major nationwide offensive, including attacks on virtually every major South Vietnamese
city, including Saigon itself. It was not until years later that NSA admitted, “SIGINT was unable to provide advance warning
of the true nature, size, and targets of the coming offensive.”
⁴⁶