No, it wasn't Marines;

in a way it was even better.
Anthony Sadler, a senior at Sacramento State University, was traveling with childhood friends Spencer Stone, an Air Force serviceman from Carmichael, California, and Alek Skarlatos, a National Guardsmen from Roseburg, Oregon, when they heard a gunshot and breaking glass.

From another story:
The 22-year-old National Guardsman from Rosenburg, Oregan, and Mr Stone charged the unidentified 26-year-old man, believed to be of Moroccan origin, down the narrow carriage.

"Then I grabbed the AK (assault rifle), which was at his feet, and started muzzle thumping him in the head with it," Mr Skarlatos added.
...
"In the aftermath, we saw that a man's throat had been split and he was bleeding profusely," Mr Sadler said.

Airman Mr Stone, who was injured himself in the hand during the tussle, performed first aid on the unidentified passenger.

Mr Sadler continued: "Spencer, who has some paramedics training, just clogged up his neck so he wouldn't die. This is all in the midst of Spencer bleeding profusely himself.”
I'm really surprised the dirtbag is still breathing, but having all those indents in his forehead helps.