When I was growing up on a farm near Evansville, I heard stories from three of my uncles about being in WWII. The military intrigued me, especially being in the Air Force. And in 1968, about a month after graduating from U of M, Morris, I talked to a recruiter and signed up. The Vietnam War had already begun almost three years before.

Stephen Thronson during his military days. Contributed photo

The first surge of 3,500 U.S. Marine troops had gone ashore in Da Nang, Vietnam, in March  1965. At about the same time, U.S. Air Force B-52s began bombing along the Ho Chi Minh Trail in Laos where the North Vietnamese military was known to cross.

This was before the development of smart bombs, and for U.S. B-52 pilots in Vietnam, traditional high-altitude bombing was quickly found to be ineffective. To get a good “fix” on a target location, pilots used off-set aiming points (like a tall building or a smokestack), which were not easily found in Southeast Asia. Most of the target locations were in hard-to-see jungle areas.

Looking for a solution, the Air Force turned to tracking technology already being used in the U.S. At the time, seven or eight radar tracking stations across the United States were training B-52 crews on simulated nuclear missions (both high and low levels). And, in late 1966 to early 1967, the government built sites in Southeast Asia to use similar technology in a different capacity. The plan was, when aircrews were deployed to Southeast Asia, the training they received in the U.S. would help them avoid being shot by SAMs (surface to air missiles); plus, using the Mercator Grid, their bombing would be more accurate.

B-52 Bombing and the Mercator Grid

Every square yard of land in Southeast Asia was mapped using a system called the Mercator Grid; giving each location an x (horizontal) and y (vertical) axis point depicted with an eight-digit number (e.g., xy16946284). The ‘x’ and the first four numbers are intersected with the ‘y’ and the second four numbers to specify the location of a target.

South Vietnam was divided into four radar tracking zones. The northernmost site was built at Phu Bai, which was in I Corps close to the demilitarized zone (DMZ), or the 17th parallel; another was near Pleiku in the Central Highlands (II Corps); a third in Bien Hoa, near Saigon (III Corps); and, the fourth site was in South Vietnam at Binh Thuy in the Mekong Delta area (part of IV Corps). Tan Son Nhut Air Force Base near Saigon was the headquarters, called Combat Skyspot. Another two sites were built in Thailand; one in Nakhon Phanom and one in Udorn.

The second part of the government’s plan was to train personnel currently working in the U.S. stations to man the overseas radar bases. The difference was, instead of using the technology as a form of defense (as they were doing in the U.S.), they were now using it to guide bombers to their targets. The ground-based radar crew ‘locked on’ to the lead bomber and directed the pilots, telling them where and when to drop their bombs.

By the summer of 1970 many of the original personnel had served up to a year in Southeast Asia and were due for leave; they needed more manpower. Again dipping from the U.S. long-range radar stations, they took six people from the different U.S. sites for relocation to the RBS site located on the Bluegrass Army Depot near Richmond, Ky. for training. I was one of those six. They told us, “We’re going to cross-train you guys for running automatic-tracking radar, and then you are going to Vietnam.”

Stephan Thronson and his group serving the Air Force during Vietnam.
Photo contributed

I was stationed for about a year at the site near Pleiku (Central Highlands, II Corps). The base was small and rather primitive, but secure. The entire site was enclosed in a 15-foot high revetment (barrier)—two layers of steel, separated by 4 feet of dirt. Sandbag shelters were connected to the revetment in case of a rocket attack. A semitrailer housed the auto tracking radar (the guts of the system) operated by two men, and an antenna slowly rotated above the trailer.

Our work area was beside our commander’s office, and contained a 4-by-5 foot plotting board, the operations room, computer operator’s desk, and the recorder’s desk, along with secure teletype manuals detailing every feasible combination of aircraft and bombs in the Air Force and Navy/Marines’ inventory. The entire site—not counting our generators 200 feet away—was about one-third the size of a football field.

There were typically 26 airmen per site:  five officers (the commander, the operating officer and three captains) and 21 enlisted airmen. The enlisted men were divided into three crews, each headed by a captain who had previously been deployed to Southeast Asia as a B-52 navigator, so they knew how the system worked. Each of the teams were scheduled in shifts, for 24/7 coverage.

A couple of hours before each bombing, our orders came in from Tan Son Nhut Airbase. The orders told us what kind of B-52s (older D-models, or newer G-models, which had more countermeasure equipment), the type of bombs they were carrying, their altitude, heading, and air speed. As the recorder, I took all the information from the orders and used the manuals to determine the exact point to drop the bomb. Our crew chief (a tech sergeant) and controller would confirm my calculations.

Most of the B-52 missions in II Corp were close to 35,000 feet high. If the bombing was further north (closer to the DMZ) they flew higher and faster; close to 40,000 feet at 400 knots true air speed. When bombs are falling close to seven miles (36,960 ft), it affected the trajectory. So, in these instances, I also called Peacock (the weather station), to get current wind speeds at two of the higher altitudes. A hand-held instrument called an MB-4 was used to determine the drift correction angle (DCA). The drift would cause heading changes, usually less than two degrees.

The computer (UNIVAC) was connected to the plotting board so the computer operator could place the Mercator Grid (xy axis) numbers on the plotting board. Then, our two plotting board operators worked backwards from the target to the point the bombs drop, and mark it on the board.

The B-52 bombers were always in a group of three, called a “cell.” They weren’t based in South Vietnam, and would have to fly in from either Utapao Airbase near Bangkok or the Andersen Airforce Base, Guam. In a typical bomb run, the lead B-52 would radio us about 30 minutes beforehand to confirm their bomb load and other statistics (altitude, air speed, etc.). “This is Red 1 calling Bongo (our code name).”

After reaching the IP (initial point of the bomb run), our controller was the only person authorized to speak with the pilot. During those next 15 minutes, if the B-52 cell drifted away from the center line, our controller would give the pilot small heading corrections, like “half a degree left.” And, as they approached the target, he would say, “5-4-3-2-1 hack,” and it was “bombs away.” Sometimes we got a photo reconnaissance to show our accuracy with a certain mission. When we were within 25 miles of the bombing, we could hear the rumbling in the distance, and we’d know.

Although the B-52 missions were our primary responsibility, we also directed many tactical fighter missions, usually two planes of either F-4 Phantoms (Navy and Air Force) or F-100 Super Sabres (strictly Air Force). If their target was “socked in” due to weather or they were “bingo fuel” (low on fuel) and they needed a target, the pilot would radio us. As you can imagine, these missions came on short notice. I’d quickly call II DASC (Direct Air Support Center for II Corp) and ask for a target. They gave me one close to the fighters, generally saying it is a “known enemy location.” It wasn’t a secure phone line, so the target was always encrypted with a code that changed every night at 2400 hours.

Stephan Thronson spent many hours in the radar room during the Vietnam War. Contributed photo

For these spur-of-the-moment missions, we still went through our steps. Our computer operator ran the xy numbers, I had the proper manual and determined at which point the bombs should drop, the crew chief and computer operator double checked for accuracy, the plotting board operator marked the target, the radio operator locked on the lead aircraft, and our controller radioed the lead fighter and got them heading to the appropriate altitude and IP. With everyone working together—fighter fuel remaining a factor—we could complete the whole mission in 20 minutes.

We generally used 12,000 feet for the bombing altitude on these missions. Most of the mountains along the trail were less than 10,000 feet, and we wanted to be a few thousand feet above the highest land elevation. The most unusual mission while I was on duty involved a C-130 Hercules with a 15,000-pound “block buster” bomb, used to flatten jungle ground so helicopter missions could take place. The Hercules was a large, four- engine cargo plane, not designed to drop bombs, and the bomb was dropped from the back cargo door.

It’s important to note, our teams were always aware of the areas we were targeting, staying at least 2,000 yards from a village, or Buddhist temple. While I was in Vietnam, we heard of one radar site that miscalculated on a block buster mission. The bomb exploded on the edge of a village and quite a few Vietnam civilians were killed. That crew was sent back to the states. Our captain and crew chief always emphasized, “check and recheck.” We dealt with a lot of different aircraft and ordinances, so it’s easy to see how miscalculations can happen.

While in Vietnam, we also had several opportunities to help civilians in our area. They had a poor, neglected way of life, and they worked hard for the little they had. There was no warm water, sewage was running on the surface of the land, and there was always a bad smell, yet the people were always friendly toward us.

The conditions of the area mandated that we take a malaria pill each day and sleep under mosquito netting at night. On one occasion, we got a shipment of Red Cross clothing, and our operations officer asked me to be his driver. We headed to a leper community to deliver the clothing. It was an eye-opening experience; something you don’t ever forget.

There were three local women who washed our clothes—on a cement pad, with a hose and Tide laundry soap; their only way to agitate the wash was to stomp on it, in a tub, like grapes. They did this for us, and we paid them three MPCs (military payment certificates) each month. U.S. currency was worth too much on the black market, so when we got to Vietnam, we all had to convert our U.S. currency to paper MPCs for buying any goods or services in the area.

The women would eat their noon meal at the barracks out of an electric skillet, and occasionally brought their young children along for a shower because we had warm water. They helped us out a lot while we were there, and I’ve often wondered what happened to them—if they had survived.

We always knew if, and when, the U.S. pulled out of the war, it would be lost to North Vietnam, because the South was unable to fight on their own. In January 1973, the U.S., North and South Vietnam, and the Vietcong signed a peace agreement. Soon after, the communists violated the cease fire, and by early 1974, full-scale war had resumed. In one year, authorities reported 80,000 South Vietnamese soldiers and civilians had been killed.

Looking back, my war experience is something I never regretted. I was able to help the local people of Vietnam, my crew and my country; and it shaped my future more than I could ever have imagined. It ended up being the story of my life.