The American pilots, told that their mission north of the central city of Najaf would be simple and safe, saw the palm trees two kilometres (1.2 miles) to their west but did not sense the approaching threat.

"They (the Iraqis) stayed silent without any radars and didn't expose themselves at all," 101st Airborne Division pilot Michael Wells, who flew one of the 20 Apaches into the ambush, recalled to AFP on Tuesday.

"They waited until we were right into their kill box and, as we turned away from them, they let loose. They had a lot of powerful weapons, artillery, air defence systems and small arms ... basically there was massive fire coming at us."

For Wells, who has been a helicopter pilot for 15 years and flown the elite Apache for 12, the surprise assault was the first time he had taken fire in his career but his experience proved enough for him to make his escape.

"As I looked out basically the aircraft was enveloped in flak. There was ammunition the size of Coke bottles flying past ... flak and black smoke was everywhere," he said.

"We dropped from 60 feet (18 metres) to 30 feet while pulling maximum power and got out of the area."

Amazingly, Wells' Apache suffered no damage but the incident did have an immediate impact.

"My first thought was we weren't going to make it to the next field or the next tree line," Wells said.

"I'd like to say (I felt) a lot of anger and retribution but it wasn't like that at all. You get a very quick sense that the next round is going to knock you out of the sky. Basically it was fear and adrenalin."

Other pilots who flew into the ambush reported even more extraordinary escapes.

A rocket propelled grenade (RPG) ripped through the bottom of Phil Munden's helicopter, passing just 15 inches behind him and out through the right hand side of the aircaft.

"The aircraft was low, we were travelling about 60 knots (72 miles an hour)," Munden, 56, recalled.

"A little guy in a black suit jumped out of a hole. He was on the right-hand side. We banked to the left to get away and he fired. The most amazing thing about it was the RPG didn't explode. The RPG is supposed to explode on impact. There's no doubt in my mind there are a lot of angels in my cockpit."

Munden said all but one of the helicopters were struck by small and medium arms fire.

"One took a bullet right up into the fuel tank and lodged itself into the coating of the tank that's supposed to make it self sealing," he said.

"A ZPU-2 (23mm twin-barreled anti-aircraft gun) got another helicopter. It had a seven-foot hole in it like somebody had opened it up with a can opener. There were holes in the four rotor blades, the tail rotor was shot up."

Just one pilot, Captain Jason Smith, was injured and he suffered only a grazed right cheek and nose from shrapnel.

The ambush effectively ended in a stalemate with the helicopters escaping but unable to find and kill the enemy.

"It's kind of embarrassing for an attack pilot," Munden said.

However, Munden and Wells said the ambush taught the Apache pilots from the 101st's Aviation Brigade a lot for later battles as they fought to secure Najaf, Karbala and Hallah, three strategically important central Iraqi towns.

"My last experience was in the (1991) Gulf War," Munden said. "That was ideal for the Apaches. It was text book. It was a turkey shoot with their tanks out in the open.

"But they haven't been sitting here for the last 12 years licking their wounds. They have gone to school and worked out a different way of fighting this war."

Wells said the ambush made them realise that their greatest dangers lay on the outskirts of the cities, not inside where infantry troops were taking on the Iraqi forces in intense house-to-house combat.

"We found resistance would spike about one kilometre (half a mile) from the city. Once you get past there it's generally pretty quiet," he said.

The lessons appear to have been well learnt with the "Palm Tree" ambush easily remaining the most dangerous mission for the 101st pilots involved in urban combat around central Iraq, and with Karbala and Najaf under US control.

SPACE.WIRE