More than 600 Americans have died in the Afghan war, and more than 4,000 in Iraq. Dozens more would certainly have died there if not for the heroism of two Marines, who Friday were awarded - posthumously - the Navy's highest honor for valor. CBS News correspondent Mark Strassmann has the story of two fallen heroes.

Six seconds. That's all it took to turn a quiet Iraqi street into a moment both horrific and heroic.

Lance Cpl. Jordan Haerter and Cpl. Jonathan Yale died so others would live.

"You're talking about two guys who gave up everything for their brothers," Staff Sgt. Kenneth Grooms said.

They were Marine brothers from very different worlds.

Yale's was hard-scrabble Virginia. From a troubled home, he hungered to belong.

"He touched your heart as soon as you met him," said Rev. Leon Burchett, who took Yale in. "He never had a whole lot, but he was thankful for what he did have."

On Long Island, New York, Jordan Haerter grew from middle-class toy soldier into mature Marine.

"He had your back, without a shadow of a doubt," said Grooms.

Last April, Yale and Haerter were guarding the entry to their platoon's camp in Ramadi.

Standing here, out of sight. It was 7:30 in the morning. They had just met.

Suddenly a suicide truck appeared. It contained 2,000 pounds of explosives, heading toward them - and dozens of sleeping Marines.

"That's like staring at the biggest, ugliest thing you could ... and standing there," said Lance Cpl. Nicholas Xiarhos, a fellow Marine.

"Almost like staring at death itself?" Strassman asked.

"Absolutely," Xiarhos said.

The Marines shot at the driver, killing him.

But then the truck erupted - its force ending a videotape of the event. It was so powerful, the blast leveled a city block.

Yale was dead. Haerter was dying.

But everyone else nearby - Marines and Iraqis - survived.

"And they made a heroic choice," Grooms said. "And it ended up saving, you know, 50 people."

Even by Marine standards, the heroism was extraordinary. The top Marine general in Iraq personally interviewed Iraqi witnesses, then nominated the two Marines for the Navy Cross.

"They made a lot of decisions in those six seconds," Maj. Gen John Kelly said. "And one of them was to die."

The tape showed an Iraqi policeman ran. He lived.

Kelly said: "They wouldn't have stood there and done that unless they were Marines, all the way to their DNA."

Haerter had a hometown hero's return on Long Island - like Yale in Virginia.

Friday at the Marine museum in Virginia, the families of Hoerter and Yale got their Navy crosses.

"None of us will ever be able to know or experience that split-second brotherhood," Grooms said.

They started the day strangers. Their shared valor made them brothers forever.