The fact that the non-descript cafe is not easy to find only adds to its character. I must have asked ten people for directions, only to discover I had passed the place several times. All that differentiates it from the hundreds of other noodle joints in the former heart of Saigon is a couple of plaques that have seen better days.

It’s still a popular spot for tourists visiting Ho Chi Minh City, and the story is kept alive by the cleaner, who is only too delighted to tell tales of his comrades’ bravery during the Vietnam War, especially that of its owner, Ngo Van Toai (below).

Toai had bought the three-storey house – 7 Yen Do Street – in 1966, and with money from Viet Cong coffers turned it into an undercover command post to co-ordinate attacks deep within American-controlled territory. He lived a double life, smiling at the diplomats and US soldiers he cooked for every day at Pho Binh (it means “peace soup”) while City Rangers from the communist north planned deadly assaults against them in a room upstairs.

A month before the 1968 spring offensive, he was told to start secretly bulk-buying rice, wheat and other foods – enough to feed 200 people a month. On the first day of the Lunar New Year, commanders gathered and encouraged the guerrillas on their certain-death mission.

The co-ordinated strikes, including one on the US Embassy in Saigon, failed tactically, but they proved a great political coup for the north. Pictures of the Tet Offensive and aftermath were beamed into sitting rooms across the world, fuelling the peace movement’s arguments that the Americans could never win the war.

The noodle shop was raided, and Toai was arrested and tortured for 20 days but he did not “open his mouth even half a word”, the cleaner said. He was sentenced to life in the notorious Con Dao prison on Phu Quoc island, and released when the war ended in 1975. He died a few years later from ill health.

“I was not afraid of death,” the old soldier explained in an interview after his release. “I had offered my home to the revolution. I cared nothing for myself. I was willing to sacrifice.”

As I sat down, where US soldiers had slurped noodles four decades before, the cleaner handed me two books. One was filled with photos and press clippings of Toai and his noodle shop, and the other was a visitors’ book, littered with observations that very little had changed in the last 40 years, and America was still involved in foreign conflicts far from its shores, this time in the name of crushing terrorism rather than communism.

The restaurant only offers two dishes – beef noodle soup or chicken noodle soup – just as it did for all those years when American forces ate there, not knowing they were just a few feet from the enemy. The cleaner pointed to the 62-year-old man making my noodles, and said he was Toai’s son. I could see the facial resemblance, and the pride in his eyes, but there was sadness too, and not just the sadness of a man who clearly has a lot to live up to.

He was cutting up meat on a wooden board. Near him were large joints of beef, covered in yellow fat that looked like melted candle wax. It was the same recipe and board his father used during the war. The cleaner prepared my chicken noodle soup, adding hoisin sauce, chilli, and lime juice, and scattering thorny coriander and basil leaves, before mixing it all carefully with chopsticks. A wide-eyed American tourist walked in and sat down behind me.

“Chicken or beef?” the cleaner asked.

I passed her the two books, and warned her about the anti-US language in one of them. She had that same slightly embarrassed look that many American travellers seem to share today when the subject of US foreign policy comes up.

When I’d finished my meal, the cleaner showed me upstairs. There was an airy kitchen out the back with steps leading up to what he called the “classroom”. It was a shrine to the Viet Cong guerrillas who had launched the attacks.

One photo showed the inner circle sitting around a small table, sipping tea and planning their bloodshed. The table was still there – despite long pleas from the communist government for it to be housed in the War Remnants Museum in Saigon.

The cleaner said he often takes pictures of tourists pretending to drink tea from the table, some of them American veterans who fought in the war, and want to make peace with their past.

In the far corner were mug shots of two women and two men, who had carried bombs into buildings and blown themselves up for the cause. He called them “heroes”. In front of a cabinet containing war medals, stood a photo of Toai in his military uniform.

“Police come many times, but they hide photo behind Buddha picture on wall, and they no look there,” he chuckled.

He showed me the narrow alley at the back of the building – so narrow the police never bothered looking there. It offered the only escape route out of the restaurant – a 30ft drop.

The rest of the three-floored building had served as sleeping rooms, but it was difficult to see how 160 people could have crammed in, even sleeping nose to foot.

As I sat there at the table, and wondered at the fear they must have felt knowing the horrific tortures that awaited them should they be caught, I imagined Toai downstairs boiling beef for his pho bo. It was ironic that Vietnam’s unofficial national dish, a meal created in the communist north, had played such a part in America’s humiliating retreat from South Vietnam.