One is in the Air Force, another recently served in Afghanistan, another is a physical therapy student - all three are being hailed as heroes for tackling and disarming a gunman they encountered on a high-speed Amsterdam-Paris train.
Air Force serviceman Spencer Stone remained hospitalised on Saturday after being stabbed in the Friday night attack, though the Pentagon said the injury was not life-threatening.
Another passenger was wounded by a handgun, according to a police union official.
Anthony Sadler, a senior at Sacramento State University, was travelling with childhood friends Stone from California and Alek Skarlatos, a National Guardsman from Oregon, when they heard a gunshot and breaking glass.
Sadler told The Associated Press they saw a train employee sprint down the aisle followed by a gunman with an automatic rifle.
"As he was cocking it to shoot it, Alek just yells, 'Spencer, go!' And Spencer runs down the aisle," Sadler said.
"Spencer makes first contact, he tackles the guy, Alek wrestles the gun away from him and the gunman pulls out a boxcutter and slices Spencer a few times.
"And the three of us beat him until he was unconscious."
Another passenger helped tie the gunman up and Stone then quickly turned to help another passenger who had been wounded in the throat, stopping his bleeding until paramedics came, Sadler said.
The identity of the person with the gun wound has not been released and it is unclear whether the victim was intentionally targeted.
Throughout the brief but terrifying episode, Sadler said, "The gunman never said a word."
It's unclear whether there was a political motive to the attack.
French counter-terrorism authorities are questioning the gunman and are expected to speak to at least one of the Americans about what happened.
French Interior Minister Bernard Cazeneuve speaking from Arras, where the train was diverted said they "were particularly courageous and showed great bravery in very difficult circumstances" and "without their sangfroid we could have been confronted with a terrible drama".
Skarlatos, 22, had returned from a deployment in Afghanistan in July and Stone is stationed in the Azores, according to Skarlatos' step-mother Karen Skarlatos.
She spoke with her step-son immediately after the incident.
"He sounded fine but he was intense - he sounded like he had just thwarted a terrorist attack."
"Alek and Spencer, they're big, brave, strong guys and they decided they were going to tackle him. And they did," she told the AP from Oregon.
"Spencer got a couple good slices on him but they were able to subdue him while the train was still moving."
