When a gunman opened fire on a 500-passenger train from Amsterdam to Paris Friday afternoon (August 21), it appeared the scene would end in a bloodbath. Armed with an automatic rifle and a handgun, the shooter made his way into a train car -- where three Americans traveling aboard sprung to action, grabbed the shooter by the neck and subdued him.

As the AP reports, two of the Americans -- Spencer Stone and Alek Skarlatos -- were members of the military, and the third, Anthony Sadler, was a childhood friend of theirs. Stone said the gunman entered their train car after they heard a gunshot and saw a train employee run quickly down the aisle.

"As he was cocking it to shoot it, Alek just yells, 'Spencer, go!' And Spencer runs down the aisle," Sadler told the AP. "Spencer makes first contact, he tackles the guy, Alek wrestles the gun away from him, and the gunman pulls out a box cutter and slices Spencer a few times. And the three of us beat him until he was unconscious."

A British man and a French man, fellow passengers, also helped subdue the shooter, who remained tied up until the police met the train at the next stop. Two were wounded before the crew took down the shooter. Stone's injuries were not life-threatening.

“I mean, adrenaline mostly just takes over,” Skarlatos said via a Skype interview broadcast on TV not long after the attack. “I didn’t realize, or fully comprehend, what was going on.”

In a statement issued by the White House, President Obama praised the "heroic" actions of these three travelers: "While the investigation into the attack is in its early stages, it is clear that their heroic actions may have prevented a far worse tragedy."

And Stone -- whom The New York Times described as a "powerfully built" -- said the three were prepared for a battle: "It seemed like the terrorist was ready to fight until the end but so were we."

Authorities identified the shooting suspect as a 26-year-old Moroccan named Ayoub El Khazzani. He's currently being investigated for possible ties to terrorist networks.

We'll have more on this story as it develops.