The Secret Sentry (19 page)

And last (but not least), despite the fact that NSA was the only U.S. intelligence agency to issue
any
warning that the North Vietnamese and Viet Cong intended to launch a major offensive in South Vietnam, NSA’s official history
of the Vietnam War sadly notes that “the [NSA] reports failed to shake the commands in Washington and Saigon from their perception
of the communist main threat centered in the north, especially at Khe Sanh, and in the Central Highlands.”
⁴⁷

The Battle of Khe Sanh

As vicious as the fighting would often be, the battle for Khe Sanh was not the decisive event that Johnson and Westmoreland
had anticipated— or the American equivalent of the 1954 Battle of Dien Bien Phu (where the French army lost an entire garrison
to the Viet Minh) that the White House was so anxious to avert.

As noted above, the Battle of Khe Sanh had commenced a week before the beginning of the Tet Offensive when the North Vietnamese
325C Division launched an unsuccessful three-battalion assault on marine defensive positions in the hills outside the firebase.
Then for the next three weeks there was a surprising hiatus while the Communist Tet Offensive raged over the rest of South
Vietnam. Newly declassified documents suggest that SIGINT played a major role in this delay. On the weekend before the Tet
Offensive began, army and air force ARDF aircraft pinpointed the location just inside Laos of the NVA “Front” headquarters
directing operations in the Khe Sanh area. On January 29, the day before the Tet Offensive began, forty-five B-52 bombers
dumped 1,350 tons of bombs on the site of the North Vietnamese headquarters, and the radio transmissions that had been originating
from the site disappeared for almost two weeks, indicating that the bombers had destroyed the enemy headquarters.
⁴⁸

It took the North Vietnamese several weeks to get reorganized. On February 7, NVA troops and tanks overran the nearby Green
Beret base at Lang Vei. But rather than presage a massive assault on Khe Sanh, the attack on Lang Vei marked the beginning
of almost three months of desultory North Vietnamese attacks on the firebase, which finally petered out in April. During this
three-month period, the marines beat off repeated small-scale North Vietnamese ground assaults, in many cases, only after
fierce hand-to-hand fighting, but no major attack on the firebase itself ever occurred. In fact, after the fall of Lang Vei
evidence appearing in SIGINT indicated that the North Vietnamese had stripped troops from the front lines around Khe Sanh
and sent them south. As a result, President Johnson and General Westmoreland’s fears that Khe Sanh would become the “American
Dien Bien Phu” never materialized. The embarrassment felt by U.S. government and military officials in Washington and Saigon
was palpable. The decisive battle with the best units in the NVA that they had hoped for never happened.

According to a declassified NSA history, the Battle of Khe Sanh was “one of the greatest SIGINT success stories ever.” Much
of the success can be credited to a tiny U.S. Marine Corps SIGINT detachment belonging to the First Radio Battalion and an
attached South Vietnamese SIGINT unit, which had been operating a radio intercept site inside Khe Sanh since August 1967.
Once the NVA attacks against Khe Sanh began, the marines started intercepting North Vietnamese artillery communications, which
allowed the unit to warn the marine commander of the base every time the NVA planned to bombard the base. The marine SIGINTers
also became expert in predicting when the North Vietnam -ese planned to attack the base. A declassified NSA document notes,
“SIGINT predicted some 90 percent of all ground assaults during the siege.”
⁴⁹

Throughout the battle, one or more army or air force ARDF aircraft continually orbited over Khe Sanh, pinpointing the sites
of NVA radio transmissions, enabling the marines to direct air strikes and artillery fire toward the North Vietnamese commanders
as they spoke on the radio. The process of locating NVA radio transmitters became so smooth that within ten minutes of a North
Vietnamese radio operator going on the air, his location was being plastered by artillery fire or tons of bombs dropped by
orbiting fighter-bombers.
⁵⁰

The casualties that the North Vietnamese suffered thanks to SIGINT were considerable. Daniel Graham, then a colonel serving
on the MACV intelligence staff in Saigon, said, “We knew . . . from intelligence that we had got our direction-finding equipment
going so well up around Khe Sanh that whenever they’d hit the [Morse] key for a minute, boom, they’d get hit. We’d get gripes;
here were [North Vietnamese] commanders on their telephones, saying, ‘I need a radio operator. My people won’t man the radios.’
Every time they’d open up with a radio, boom! There comes shot and shell . . . Oh hell, you know, you got to the point where
you kind of sympathized with these poor bastards out there under that kind of shot and shell.”
⁵¹

The Invasion of Cambodia

By early 1970 the Nixon administration was secretly planning to expand the war into neighboring Cambodia. In February, President
Richard Nixon authorized a massive secret bombing campaign against North Vietnamese base camps and supply depots there. On
March 18, Cambodian leader Prince Norodom Si-hanouk was overthrown in a coup d’état led by the Cambodian defense minister,
General Lon Nol.
⁵²

On April 30, Nixon ordered U.S. troops to cross into Cambodia and wipe out the vast network of North Vietnamese military headquarter
complexes and base camps inside the country. Demonstrations immediately erupted across America, which led to the tragic encounter
between Ohio Army National Guard troops and student protesters at Kent State University, which left four students dead.

So secret were the administration’s plans that neither NSA nor the military SIGINT units in Vietnam were sufficiently forewarned.
Lieutenant Colonel James Freeze, the commander of the ASA’s 303rd Radio Research Battalion at Long Binh, did not find out
about the invasion until April 28, two days before it was due to begin. There was not a lot that NSA and the military SIGINT
units in Vietnam could do in forty-eight hours to prepare for the invasion.
⁵³

One of the main objectives of the invasion was to capture or destroy the headquarters of all North Vietnamese and Viet Cong
forces fighting in South Vietnam, which was known as the Central Office, South Vietnam (COSVN). SIGINT collected prior to
the invasion showed that the COSVN headquarters complex was located somewhere just inside Cambodia opposite Tay Ninh Province
in South Vietnam. Throughout the incursion, U.S. Army and Air Force ARDF aircraft were able to track the movements of COSVN
by listening to its radio transmissions as it retreated deeper into Cambodia, always well ahead of the slow-moving U.S. and
South Vietnamese forces, which, SIGINT showed, never came close to capturing the headquarters.
⁵⁴

The invasion of Cambodia prompted the North Vietnamese to expand their control over eastern Cambodia. By the end of May 1970,
all U.S. and South Vietnamese forces had retreated back across the border into South Vietnam, and the North Vietnamese military
was left with complete control over all of northeastern Cambodia. As an NSA historian put it, “few operations in American
military history had such dismal consequences.”
⁵⁵

This Is the End

On January 27, 1973, Secretary of State William Rogers and his North Vietnam -ese counterpart, Le Duc Tho, signed the Paris
Peace Agreement, and the last remaining U.S. forces were withdrawn from South Vietnam two months later, including the last
remaining U.S. military SIGINT collection units. After the U.S. troop withdrawal was completed, in late 1973, the only remaining
NSA presence in the country was the agency’s liaison staff in Saigon, as well as several hundred U.S. Army advisers who were
engaged in trying to train and equip the South Vietnamese SIGINT service.
⁵⁶

Things remained relatively peaceful until the fall of 1974, when SIGINT reporting coming out of NSA began indicating that
the North Vietnamese were openly building up the strength of their military forces inside South Vietnam. SIGINT clearly showed
that huge numbers of North Vietnamese troops and supplies, including tanks and armored vehicles, were flowing down the Ho
Chi Minh Trail, and they were no longer being hindered by American air strikes. By January 1975, SIGINT showed that the North
Vietnamese military buildup in South Vietnam had been completed. Everyone in Washington knew that the “final offensive” was
coming soon.
⁵⁷

The collapse of South Vietnam began with the North Vietnamese conducting a probing attack in January 1975 in Phuoc Long Province,
in southern South Vietnam. After a short fight, the province swiftly fell, a preview of what was to come. Despite all SIGINT
indications of a continued North Vietnamese military buildup throughout the south, on February 5 the CIA’s intelligence analysts
made this prediction: “While we expect localized heavy fighting to re-sume soon, there are no indications of Communist plans
for an all-out offensive in the near future.” On February 18, the CIA predicted, “heavy North Vietnamese attacks” by the end
of the month, with the expected focus of the new offensive to be Tay Ninh City, north of Saigon.
⁵⁸

The CIA analysts could not have been more wrong. In March, the all-out North Vietnamese offensive commenced, not around Tay
Ninh but across northern South Vietnam and the Central Highlands. NSA and South Vietnam -ese SIGINT somehow failed to detect
the presence of at least three North Vietnamese divisions in the Central Highlands until the attacks began. City after city
fell in rapid succession, and by the end of March the entire Central Highlands had been abandoned to the North Vietnamese.
The NSA representative at the South Vietnamese SIGINT intercept center in Pleiku barely managed to get out of the city before
it fell. As North Vietnamese forces streamed south virtually unopposed, the old imperial capital of Hué fell on March 22.
In mid-March, SIGINT had detected a number of North Vietnamese strategic reserve divisions being hastily moved into South
Vietnam for the final push.
⁵⁹

As the North Vietnamese forces pushed southward toward the city of Da Nang, on March 26 NSA ordered the sole agency officer
assigned to the South Vietnamese listening post in the city to get out immediately. The NSA officer drove to the Da Nang airport
and managed to talk his way on board one of the last Boeing 727 aircraft to get out of the city. An NSA history notes, “He
rode the overloaded airplane to Saigon with a Vietnamese child on his lap.” Da Nang fell to the North Vietnamese four days
later.
⁶⁰

As the North Vietnamese brought up reinforcements and supplies for the final push to take Saigon, a few hundred miles to the
west the forces of the Cambodian government were rapidly collapsing. Since the U.S. invasion of Cam bo-dia in April 1970,
the North Vietnamese–backed Khmer Rouge forces had me thodically captured most of the country from President Lon Nol’s poorly
led government forces. By January 1975, Lon Nol’s troops held only a tiny island of territory surrounding the capital of Phnom
Penh, and SIGINT reporting coming out of NSA and from U.S. military units based in neighboring Thailand showed that the Khmer
Rouge were inching closer to the besieged capital. On April 11, a U.S. Air Force SIGINT unit in Thailand intercepted a message
from the Khmer Rouge high command ordering the final assault on Phnom Penh. Ambassador John Gunther Dean was immediately ordered
to evacuate all employees of the U.S. embassy and any other Americans remaining in Cambodia. U.S. military helicop ters had
completed the evacuation by the end of the day on April 12. The city fell to the Khmer Rouge the next day.
⁶¹

In Saigon, Ambassador Graham Martin refused to believe the SIGINT reporting that detailed the massive North Vietnamese military
buildup taking place all around the city. He steadfastly disregarded the portents, even after the South Vietnamese president,
Nguyen Van Thieu, and most of his ministers resigned and fled the country. An NSA history notes that Martin “believed that
the SIGINT was NVA deception” and repeatedly refused to allow NSA’s station chief, Tom Glenn, to evacuate his forty-three-man
staff and their twenty-two dependents from Saigon. Glenn also wanted to evacuate as many of the South Vietnamese SIGINT staff
as possible, as they had worked side by side with NSA for so many years, but this request was also refused. NSA director Lieutenant
General Lew Allen Jr., who had taken over the position in August 1973, pleaded with CIA director William Colby for permission
to evacuate the NSA station from Saigon, but even this plea was to no avail because Martin did not want to show any sign that
the U.S. government thought Saigon would fall. So Glenn disobeyed Martin’s direct order and surreptitiously put most of his
staff and all of their dependents onto jammed commercial airlines leaving Saigon. There was nothing he could do for the hundreds
of South Vietnamese officers and staff members who remained at their posts in Saigon listening to the North Vietnamese close
in on the capital.
⁶²

By April 24, 1975, even the CIA admitted the end was near. Colby delivered the bad news to President Gerald Ford, telling
him that “the fate of the Republic of Vietnam is sealed, and Saigon faces imminent military collapse.”
⁶³

Even when enemy troops and tanks overran the major South Vietnamese military base at Bien Hoa, outside Saigon, on April 26,
Martin still refused to accept that Saigon was doomed. On April 28, Glenn met with the ambassador carry ing a message from
Allen ordering Glenn to pack up his equipment and evacuate his remaining staff immediately. Martin refused to allow this.
The following morning, the military airfield at Tan Son Nhut fell, cutting off the last air link to the outside.