My son, said a visibly shaken American father, left his Sacramento home to travel abroad for the first time, as a “young man on an excursion to broaden his world view and have fun with his buddies”. Now, said Tony Sadler, he’ll be coming back “as France’s national hero”.

As two presidents, Barack Obama and François Hollande, poured praise on four men whose actions averted a bloodbath on the 3.17pm train from Amsterdam to Paris, with 550 passengers onboard, the details of what happened on the Thalys express 9364 emerged in shocking detail.

It was at 5.45pm, as the train crossed the Belgian border into northern France, that a 28-year-old French bank worker left his seat and tried to get into the toilet on coach 12. The door opened on a shirtless dark-haired man, in white trousers and trainers, who was holding a Kalashnikov across his bare chest. Inside his rucksack were nine full magazines of ammunition, holding 280 rounds, and several knives. Somewhere he also had a handgun.

Over the next few seconds there was chaos. A shot rang out, a French-American passenger fell forward in his seat, hit in the neck by a bullet from a handgun. Then came a terrifying “click, click, click” as the half-naked man held his AK-47 aloft, aiming an apparently temporarily jammed gun at occupants of the carriage.

As panicking passengers, helpless in their seats, realised there was an armed man in their midst, the train crew ran through carriage 11 towards the guardroom at the end of the train, barricading themselves behind a steel door, leaving people outside banging on it.

Meanwhile, in carriage 12, three American childhood friends had been sitting chatting about their night ahead in Paris. They were Anthony Sadler Junior, 23, a final-year student from Sacramento State University, Alek Skarlatos, 22, a member of the Oregon national guard, who was on holiday after a tour of duty in Afghanistan, and Spencer Stone, a member of the US air force. It was the sound of the gun being breeched that caught the soldiers’ attention.

“I just looked over at Spence and said, ‘Let’s go’. He jumped up and ran, grabbed the guy by the neck. I got the handgun off him and threw it,” Skarlatos told reporters afterwards.

Facebook Twitter Pinterest Three of the four men who tackled a gunman on a train en route to Paris speak to the press about their actions

But Sadler said Stone had to run the length of the carriage in full sight of the gunman. “We didn’t know if the gun wasn’t working or anything like that. Spencer just ran anyways and if anyone had gotten shot, it would have been Spencer and we’re just very lucky that nobody got killed.”

Chris Norman, 62, a British man living in the south of France, was sitting working on his laptop. “I heard a shot. I heard some glass breaking, then I saw someone running down the aisle towards the front of the train. I stood up to see what was happening and saw a man carrying some kind of a machine gun. My first reaction was to sit down and hide. Then I heard someone, an American, say, ‘Go get him,’ then another American saying, ‘Don’t do that buddy’.

“I thought it was the only chance to act as a team and try to take over the terrorists. I thought there might be more than one. Spencer overpowered the terrorist in a neck lock and then Alek was in the process of taking his gun. I grabbed his right arm. There was a French man, I think a train driver, who came to take the left.” Norman used his tie to bind the gunman.

France train shooting: gunman 'had been in Syria and was known to intelligence services' Read more

“Alek went to see if there were other terrorists in the train; at that moment we saw an injured person bleeding. Spencer was already hurt: he had almost lost his thumb and was cut several times on the neck. But he intervened because he said he was a medic. It’s very difficult to understand what happened. My thought was, ‘I’m probably going to die anyway so let’s go’,” Norman said.

“I don’t know why he didn’t succeed in firing. I think his weapon jammed. We’re very lucky. What can you do? Either you sit down and die, or you get up and die. We’ve seen enough of these kind of attacks to know that they will kill everyone once they get started. It was purely a matter of survival.”

Norman added: “I just want to go home and spend some time with my family.”

The attacker, Ayoub el-Khazani, a 25-year-old Moroccan known to European intelligence agencies, pleaded with the Americans to give him back his gun, said Sadler. “But we just carried on beating him up and immobilised him and that was it.”

Video footage from passengers inside the train shows the man face-down on the ground, groaning but apparently unconscious, while a shirtless Stone, smeared in blood, administers first aid to the injured passenger next to him. As other passengers searched on the floor for the handgun, the train driver can be heard over the PA system asking train crew to contact him.

Facebook Twitter Pinterest Video shot on a mobile phone shows the moments after three US citizens, two of whom were military personnel overpowered a gunman on a high-speed train travelling between Amsterdam and Paris

Stone was moved on Saturday to a specialist hospital in Lille with cuts to his hands and neck. “We’ve called him and he’s doing great, he’s in disbelief that it happened,” said Sadler. The other passengers’ injuries were not life-threatening, French authorities said.

Also hurt was the French actor Jean-Hugues Anglade, known for film roles in Betty Blue and Nikita, who cut his finger to the bone smashing the emergency stop handle to try to halt the train. He gave a graphic account of his ordeal to Paris Match, criticising train staff for refusing to open their steel door even after the gunman had been overcome. Anglade was in coach 11. “We heard passengers shouting in English ‘He’s shooting! He’s shooting! He has a Kalashnikov’. I was with my two children and my partner,” he said.

“Around us there were another 15 or so passengers. Suddenly, members of the train crew ran down the corridor, backs hunched. Their faces were blanched white. They ran towards their guardroom. They opened it with a special key, then locked themselves inside. The gunman was a few dozen metres from us in coach 12. [He was] coming towards us and seemed determined. I thought it was the end, that we were going to die, that he was going to kill us all. We could see ourselves die because we were stuck in the train and it was impossible to escape this nightmare. We were trapped.

“I broke the glass to pull the alarm cord to stop the Thalys. The glass cut my middle finger to the bone and the engines slowed. But we were still trapped inside.

“With our backs to the wall, huddled together one against the other against the metal door of the guardroom we shouted for the staff to let us in. But … nobody replied. Radio silence. This abandonment, this distress, this solitude was terrible and unbearable. For us it was inhuman. Minutes seemed like hours. I protected my children with my body, telling them everything would be fine. My hand was bleeding a lot, but surprisingly we kept our cool.”

He added: “Then a young man, Anthony Sadler, ran into our coach shouting that the gunman had been overcome by off-duty American soldiers and that everything was fine. He was looking for blankets and a first-aid kit for the two seriously injured. He knocked on the door of the guardroom, but once again there was no answer.”

Christophe Sargollo, a rail union spokesman, told BFMTV that the Thalys staff had acted “for the best security of the train”. “I insist on congratulating them on their sang-froid,” he said.

Most of the congratulations pouring in were for the heroes of carriage 12. The French prime minister, Manuel Valls, described the Americans as “especially courageous” and said they had “shown their bravery in extremely difficult circumstances”.

“We express all our gratitude, recognition and admiration for the sang-froid that they showed, without which we could have perhaps faced a terrible drama,” Valls added.

All three, along with Norman, were awarded bravery medals by the mayor of Arras, the town where the train finally stopped, and where the gunman was taken off by anti-terrorist officers. He is now being held at the specialist terrorist brigade headquarters at Levallois-Perret near Paris.

As a bemused Sadler senior and his wife Mariah faced television crews in California, he said he was just grateful no one had been killed.

“We live in a falling world that is full of good and evil,” he said. “I don’t know that there is a safe place anywhere to shelter your children.” He had heard that his son was to meet President Hollande. “I’m still wrapping my head around that right now.”