It's the most serious incident so far in the battle for Marja. A bomb exploded as two detainees were being questioned. It's still not clear whether it was a booby trap set in a building, an IED or a suicide bomber.
The aftermath was horrific, marines quickly assembled a makeshift triage center, preparing the casualties to evacuate the battlefield, carrying fellow troops to safety.
There were so many casualties that it took three medevac helicopters to transport them all.
The amount of time from the moment the bomb went off, to medivac lift-off was just about 15 minutes. As helicopters ferried away the casualties, Taliban insurgents fired trying to bring them down.
The explosion followed a day of intense fighting. Afghan troops moved in large numbers across southern Marja.
"There are four compounds in this area now controlled by the Taliban," says Lt. Col. Dastager, battalion commander of the Afghan National Army. "My men are headed in there to take them out."
On one of the main north-south roads here in Marja, Afghan forces fought on either side. After several hours of battle, they linked up with another force of Marines and Afghan commandos who have been fighting for five days.
It's the latest piece of Marja to fall under control of international forces and one of the most important tests for the Afghan army.
The Afghan troops are motivated, and they relish a fight. But they still need Marine muscle in the form of heavily armored MRAPS, sophisticated bomb detecting vehicles and air support, to back them up.
"[The Afghan army's] doing good, I mean they are doing really good," says Sgt. Chris Howe of the Second Amphibious Assault Battalion. "Their eagerness to get involved, their tactics are sound, they are willing to fight for their own country."
Sgt. Howe's battalion, which suffered no casualties today, never fired a single shot. With so many friendly forces in the area, all they could do was watch.
"We took a couple rounds to our vehicle. It was a little...out there," says Cpl. David Olsen.
Tonight, U.S. Marines say they control all the main roads, bridges and government buildings in the city. A battle going well, but with so many casualties today, it comes at a very high price.