He was supposed to have been headed home to see his wife. Instead, Colonel Chaicharn Harnnawee spent nine years in captivity during the Vietnam War, learning to tap code through the walls of the Hanoi Hilton and signaling to John McCain.
It was 1965 when Chaicharn, then a sergeant in the Royal Thai Army, was stationed in Laos as a radio operator. A former paratrooper, the then 35-year-old had begun to prepare for his upcoming 10-day leave to see his wife of six years.
Learn more about GOP presidential candidate John McCain tonight: Watch Diane Sawyer's "Portrait of a President" on "20/20" at 10 p.m. ET.
Chaicharn was sent May 21 on a special supply mission to another camp in Laos. With him was American pilot Ernest Brace, who would later be referred to as "America's longest-held civilian prisoner of war in Vietnam."
"[Brace] had volunteered as a civilian pilot to fly supply missions in Laos for the United States Agency for International Development," McCain wrote in his book "Faith of My Fathers," "and, when asked, to secretly supply CIA-supported military units in the Laotian jungle."
Dressed in plain clothes, Brace flew the Thai sergeant and three other passengers --a Laotian solider, a woman and her young child -- on a small plane to Boum Lao village.
They were attacked by gunfire moments after they landed. "He don't know the enemy ambush over there," Chaicharn, now 78, said of Brace from his home, about a two-hour drive from Bangkok.
The solider, woman and child were instantly killed.
Communicating Without Words
Chaicharn and Brace, with a language barrier between them, tried to escape by taking off again, but their engine had been hit and their plane caught fire.
"American pilot he saw [about] that, he get out from the airplane and we run from the airplane to the other side of the enemy in the jungle," Chaicharn said.
Traveling as civilians and with no weapons to protect them, it didn't take long for the two to be surrounded and captured.
"In the front, in the side, in the left, in the right, have many, many," Chaicharn said of the Pathet Lao who caught them and turned them over to the North Vietnamese.
It would be nine years until Chaicharn's wife would see him again -- and eight years before she knew he was even alive.
For 13 days, Chaicharn and Brace were forced to walk high into the mountains to Dien Bien Phu, the location they had overheard from the Vietnamese. At night, both thought by their captors to be from the CIA, their hands and feet were bound to prevent escape.
The two prisoners were held in the jungle of northwest Vietnam in separate small bamboo huts, about two yards long and one yard wide, for more than three years.
They would cough to let each other know they were still alive.
Brace tried to escape three times and once managed to get away for a few days. He was caught, and as a result, they both were punished.
The American pilot was once buried to his neck in the ground for days.
For the time they were held there, Chaicharn said he never saw Brace, but he would hear him and knew he was being abused.
"I heard his voice," he said. "He cried loudly and I knew."
Chaicharn showed how, for years, he was forced in a seated position -- his legs locked into holes cut in a piece of wood, his neck held back in place with iron piping and his hands tied together with rope.
They had two 15-minute breaks a day, were fed rice and ate "no meat, no pork, no egg, no fish," the Thai POW said.
There were times when the men who brought them food would slip them cigarettes, but once discovered, communication ceased.
Chaicharn would barely speak, instead listening to the sounds of the birds and animals in the jungle around him.
"Sometimes I singing," he said. He sung songs close to his heart and recalled one written by a former Thai army commander. His captors would silence him at gunpoint.
Back in Thailand, Chaicharn's wife still knew nothing about the whereabouts of her husband.
"I live or I die, she doesn't know," he said.
Moving to Hanoi
In October 1968, Chaicharn and Brace were loaded into a Jeep and rode for three days with 13 Vietnamese soldiers watching over them.
Chaicharn spotted a sign through a hole in covering over his eyes. It read, "100 km to Hanoi."
The prisoners were being upgraded to the Hanoi Hilton.
McCain, captured the year before, remembers the day they arrived.
"In October 1968, I heard the guards bring a new prisoner into the camp and lock him into the cell behind mine," the GOP presidential nominee wrote in his book.
It took days for McCain to elicit a response from Brace. He tried tapping and speaking through the walls using a drinking cup.
"I'm Lieutenant Commander John McCain. I was shot down over Hanoi in 1967. Who are you?"
"My name is Ernie Brace, came the response."
"Are you in the Air Force? Navy? Marine?"
"My name is Ernie Brace."
"Where you shot down?"
"My name is Ernie Brace."
"To my every query, Ernie could only manage to say his name before he broke down. I could hear him crying," McCain wrote. "After his long, awful years in the jungle, the sound of an American voice, carrying with it the promise of fraternity with men who would share his struggle, had overwhelmed him.'"
Chaicharn had been separated from Brace.
"When I get to Hanoi, [they] put me in a small room and I was alone again," he said.
One of three Thai prisoners, Chaicharn noted the conditions in Hanoi were better than in Laos "because it was big, not too hot. In the night we have the [mosquito] net and the blanket."
Their rooms measured three yards by more than six yards. And with noticeably higher ceilings, Chaicharn also had a small window. He used his 30- to 60-minute daily breaks to strengthen his legs and eventually he was able to run.
Meals were upgraded also and included French bread, soup, a variety of vegetables, and sometimes pork. American songs and English would blast through a loudspeaker.
The Thai government wasn't aware that prisoners from their country were at this prison, so the Thai nationals were pretty much left alone, according to Chaicharn, who also spent months at another camp in Hanoi. It was the Americans who were used for leverage.
Chaicharn says he could see and hear the Americans being beaten.
"The North Vietnamese asked many questions. Somebody not answer, [they were] beat," he said, adding that this was common knowledge among the prisoners.
Tapping for Survival
In time, McCain and Brace began to engage in frequent communication through the prison walls.
"He found out what year I had been captured, how old I was and that I had been a Marine Corps pilot in Korea, but was flying as a civilian during this war," Brace wrote of McCain in an American Legion magazine.
"I was somewhat surprised to learn he was a civilian," McCain wrote of Brace in his book. "I assumed he was CIA, but refrained from asking him."
"I'll never forget the tapping to each other, and the leadership and inspiration that I got from those people who were far better and stronger men than I am," McCain told ABC News' Diane Sawyer.
Tap by tap, Chaicharn also learned the tap code -- along with English -- from the Americans. Hiding the codes from the guards, he communicated to his neighbor each morning and night.
He demonstrates tapping the word "my" explaining how this code is different from Morse code, which is made up of dots and dashes.
Two taps plus two taps for the letter "M." Five taps plus four taps for "Y." For the receiver, two rapid taps signals "understood" or "proceed," while a series of rapid taps signals "don't understand" or "repeat."
"It's too long," Chaicharn said with a laugh.
The prisoners would trade information they learned or spotted from within the camp walls, trying to figure out any bit of news, like simply how many people were kept there.
They would secretly dig holes through the walls with pieces of stolen iron so they could talk instead of tap, and pass candy and cigarettes back and forth.
Chaicharn remembered seeing McCain in Hanoi.
"I saw him in the kitchen, wearing short pants," Chaicharn said, noting that he was skinny.
He noticed something was wrong with McCain's legs. "His leg was bad, he wounded, I think."
"I asked him, 'How are you? Are you okay?'" Chaicharn said, showing how he signaled. McCain signed back he was okay, and asked in return, "You?"
In 1973, two months after the peace treaty was signed, the American prisoners in Hanoi were released back to the United States.
Because Chaicharn was Thai and first captured in Laos, he had to stay behind.
"It was quiet," he said.
Going Home at Last
Chaicharn was the very last prisoner of war to check out of the Hanoi Hilton.
And his time in captivity wasn't over. He was transferred again, this time further north in Vietnam to near the China border, where he was held with over 200 other Thai POWs.
The recently released American prisoners he met in Hanoi did not forget him.
Chaicharn credited American John P. Flynn for keeping his word and helping him get out. The Hanoi prisoners had made a pact -- that whoever got out first would tell their government to let the other country's government know there were still POWs in Hanoi.
And it was in 1973 that Chaicharn's wife found out he was still alive. She promptly divorced her then-husband of about a year.
After nine years in captivity, Chaicharn was finally released on Sept. 29, 1974 and reunited with his wife and his mother. His father had passed away while he was in prison.
Upon his return to Thailand, the sergeant was promoted to Captain by his Majesty the King. Later, the American POWs invited Chaicharn and his wife on a one-month tour of the United States where he met with the press, traveled to the nation's capital and visited POW families, including McCain's.
For his bravery at the Hanoi Hilton, Chaicharn was awarded a Silver Star and Legion of Merit.
Chaicharn and his wife have a daughter and two grandchildren, a 5-year old boy and 3-year-old girl.
"They are lovely," the retired Colonel said from his home in Thailand.
Nearby, sits an old black and white photo framed of him and Ernie Brace.
Thank you to Dave Walker for the introduction to Colonel Chaicharn Harnnawee.