Capt. Kevin Butler couldn't believe his eyes. 

Just before the U.S. missiles would hit, Al Qaeda fighters would duck into caves from their positions launching mortars at Butler's troops below. 

When the F-15 Strike Eagles were gone, the enemy fighters would emerge — only to throw stones, wave and shout taunts at the Americans in a show of defiance. 

"I've never been so frustrated and angry," said Butler, 30, from Pattenburg, N.J. 

Frustration was coming easy to the U.S. troops of the 101st Airborne Division. They were facing a well-armed and well-entrenched foe. They'd had little sleep and were shivering in subfreezing temperatures that left many of their uniforms tinged with frost. 

The Americans were preparing to flush out enemy fighters on ridges overlooking their positions, their piece of action on the second day of the biggest joint offensive yet in the Afghan war. 

The first sounds of incoming artillery and heavy machine-gun fire cut through the air. The mortar bursts came slowly at first, then intensified as Al Qaeda and a few Taliban holdouts zeroed in on some 200 soldiers hidden in a deep stone riverbed that had dried up long ago. 

The U.S. soldiers called headquarters to request airstrikes on the enemy in the caves. But the fighters were resilient. 

"We were moving our command post to high ground," said Cpl. Jeremy Gaul, 25, from Marietta, Ohio. "When I looked out on the horizon I saw a flash of light and I saw a projectile coming and fall to the earth. It must have exploded no more than 30 yards away." 

Butler requested another airstrike, watching through a scope. Again the enemy fighters disappeared into caves dug into the granite, snowcapped mountains at 9,000 feet. When the explosions ended, they emerged with wide grins, flailing their arms over their heads. 

That's when Butler had enough. He sprinted forward, running uphill on the peak — a task made more difficult by the thin mountain air — and exposing himself to hostile fire so he could pinpoint his enemy. 

Getting a read on their location, he raced 45 yards back to relay the coordinates to his radio man behind him. He needed six trips before he could make sure he'd gotten all the data he needed. 

Now he was ready to put his own plan into action: His forces would launch 60 mm mortars just as the jets roared toward the caves — a risky proposition because it placed the planes in danger of being struck by friendly fire. 

The jets roared ahead, and just like before, the enemy ducked into the caves, emerging for a third time to taunt the Americans. 

But as they came out, the mortars detonated over their heads, spraying the Al Qaeda fighters with shrapnel. Four of them died, said U.S. special operations soldiers who scaled the mountains and counted bodies. 

"It was like a game of mortar pingpong," Butler said. "They might think twice before they try that move again." 

The Al Qaeda fighters could get a few more chances; the Gardez area offensive is expected to continue for a few more days at least. U.S. forces are pursuing Al Qaeda and Taliban forces together with Afghan commanders who have sent in thousands of fresh troops for a final push. 

With pockets of Al Qaeda forces dug in, allied forces are trying to clear several enemy caves honeycombed across the rugged terrain of Paktia province. Hundreds of Al Qaeda fighters are believed to be in the area. 

Butler and soldiers in the Alpha company, 187th Infantry Regiment of the division's 3rd Brigade, were still fighting in the lunar-like Paktia landscape late Wednesday. He doesn't even know he's being recommended for a Bronze Star by his unit commanders. 

"These guys were trying to be clever," Butler said just after the mortar match. "I guess they don't like it when we hit back."