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Trapped by intense hostile fire and unable to evacuate their wounded for 12 hours, a detachment of American Special Forces troops fought off an Al Qaeda ambush in some of the most grueling and gruesome combat of the 5-month-old war in Afghanistan, officials said Tuesday.

When it was over Monday, the bodies of seven American servicemen and 11 wounded comrades were lifted off the battlefield under guard of AC-130 gunships. Their machine guns and cannons drove back the advancing fighters–but not before commanders monitoring airborne surveillance video had seen Al Qaeda fighters dragging off one American, military officials said. The Navy SEAL was later found dead.

Important new details of a set of combat operations that began Sunday and were waged over a sprawling battlefield emerged as Pentagon officials said the hard-core Al Qaeda and Taliban fighters making a last stand in eastern Afghanistan suffered heavy casualties–but also surprised American forces by their fierce resistance.

“I don’t think we knew what we were getting into this time, but I think we’re beginning to adjust,” Sgt. Maj. Mark Nielsen told a reporter in the Pentagon press pool for the operation.

Some of the heaviest fighting of the war also brought the heaviest American combat losses, with Pentagon officials and senior military officers describing a battlefield where the topography allowed opposing fighters, who seemed willing to fight to the death rather than surrender, to charge and then retreat to fortified caves and trenches.

One of the American commandos killed was a Navy SEAL, Neil Roberts, 32, who tumbled from one of two MH-47 Chinook helicopters that was to carry in special operations forces. Just as the helicopters touched down about 4:30 p.m. Sunday Central time–in the dark of night in Afghanistan, where it is 10 1/2 hours later–one of the helicopters was struck by a rocket-propelled grenade, officials said. Both lifted off quickly and flew about a mile, where they set down again to check for damage.

That was when they realized that Roberts was not on board. But commanders had access to real-time surveillance videos shot by a Predator, an unmanned airborne vehicle, and they saw his capture.

“We saw him on the Predator being dragged off by three Al Qaeda men,” said Maj. Gen. Frank Hagenbeck, commander of the 10th Mountain Division, based at Ft. Drum, N.Y., who is in charge of the ground operation in Afghanistan.

One of the two helicopters flew back to where Roberts was lost and dropped off its special operations team to try to rescue him.

In addition, Hagenbeck, speaking to reporters in a Pentagon press pool in Afghanistan, said that “a quick reaction force of about 30 special operations troops” was also sent to rescue him.

“We don’t leave Americans behind,” said Brig. Gen. John Rosa, deputy director of operations for the Joint Chiefs of Staff.

By about 8 p.m. Central time Sunday, two more Chinooks touched down about a mile or so from where the Navy SEAL was last seen. The opposing forces apparently had set up an ambush and were waiting.

One Chinook was able to drop off its special operations team and depart; the other was riddled with machine-gun fire and hit by grenades and could not fly.

“A large number of the enemy advanced on them,” a senior military officer said. The Americans fought back, setting up fighting positions and calling in attack jets as well as AC-130 gunships that brought a withering fire of heavy machine guns and cannons, the Pentagon said.

Before they were rescued by helicopter 12 hours later, six Americans had been killed and 11 more wounded.

The body of Roberts was also carried aboard the rescue helicopter. He died of a bullet wound, military officials said.

American combat troops for Operation Anaconda told a Pentagon pool reporter from The Associated Press harrowing tales of being pinned down by hostile fire.

Elements of the 10th Mountain Division were pinned down Saturday after taking fire from the town of Marzak. Lt. Col. Frank LaCamer, who was among those trapped, said about 40 troops of the 10th Mountain Division spent 12 hours under fire from mortar and rocket-propelled grenades that landed within 15 yards, wounding 13.

And Col. Frank Wiercinski, a brigade commander for the 101st Airborne, said that shortly after he landed south of Sirkankel to survey the battle, his detachment of about 11 men was attacked and pinned down.

Sgt. Maj. Nielsen’s detachment came under fire before seizing an Al Qaeda compound a half-mile from Sirkankel. When they arrived, they made a startling discovery.

“It was unbelievable: In the mud hut where these guys slept, the beds were still warm and tea was still brewing,” he said.

The strain of continuous operations at high altitude has prompted American officials to ready troops to replace the Americans on the ground, military officials said, although the numbers of American fighters on the battlefield had not grown in the past 24 hours.