Ain al-Asad Air Base (Iraq) (AFP) - Moments after volleys of Iranian missiles began to batter Iraq's Ain al-Asad airbase, US soldiers at the desert facility lost contact with their ultra-powerful -- and expensive -- eyes in the sky.

At the time the attack was launched at 1:35 am on January 8, the US army was flying seven unmanned aerial vehicles (UAVs) over Iraq to monitor bases where US-led coalition forces are deployed.

They included MQ-1C Gray Eagles, advanced surveillance drones that can fly for as long as 27 hours and carry a payload of up to four Hellfire missiles.

"We thought it may lead to a ground assault, so we kept the aircraft up," said one of the pilots, 26-year-old Staff Sergeant Costin Herwig.

Herwig was flying a Gray Eagle when the first Iranian missile struck the base, retaliation for the January 3 killing of top Iranian general Qasem Soleimani in a US drone strike in Baghdad.

Most of the other 1,500 US soldiers had been tucked away in bunkers for two hours, after advance warning from superiors.

But 14 pilots had stayed in dark containers-turned-cockpits to remotely fly the "birds" and monitor essential feeds from their high-powered cameras.

A US soldier walks past a drone at the Ain al-Asad airbase in the western Iraqi province of Anbar (AFP Photo/Ayman Henna)

The first missile blasted dust into their shelter but the pilots stayed put, Herwig told AFP during a press tour of the base organised by the coalition.

The next rounds came closer and closer, and the light-haired soldier recalled that he had "accepted fate".

"We thought we were basically done," he said.

- 'There was no control' -

But the real crisis was yet to come.

The volleys of missiles, which soldiers said lasted about three hours, slammed into sleeping quarters directly adjacent to the pilots' operations rooms.

"No more than a minute after the last round hit, I was heading over to the bunkers on the far back side and saw the fire was burning all through our fibre lines," said First Sergeant Wesley Kilpatrick.

Extensive damage at Ain al-Asad military airbase used by US and other foreign troops in the western Iraqi province of Anbar after Iran last week launched a wave of missiles at the sprawling desert facility (AFP Photo/Ayman HENNA)

Those lines link the virtual cockpits to antennas then satellites that send signals to the Gray Eagles and pull the cameras' feeds back onto the screens at Ain al-Asad.

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"With the fibre lines burnt, there was no control," said Kilpatrick.

The soldiers could no longer locate the drones and were left blind to events in the air -- and on the ground.

If a drone had been shot down, for example, the besieged teams at Ain al-Asad could not have known.

"It's a pretty big deal, because it's so expensive and there's a lot of stuff on them that we don't want other people to have or the enemy to get," said Herwig.

A single Gray Eagle costs around $7 million, according to 2019 army budget estimates.

They have been used in Iraq since at least 2017 by the coalition to help fight the Islamic State jihadist group.

The coalition is required to get a green light from the Iraqi government to fly drones and planes, but those permissions had expired several days before the Iran attacks.

US army drones on the tarmac at the Ain al-Asad airbase in the western Iraqi province of Anbar (AFP Photo/Ayman Henna)

The US army had kept the drones in the air anyway, a senior American defence official told reporters, after months of rocket attacks on Iraqi bases where their forces are based.

- Beat the clock -

As the bombs crashed closer on January 8 and with the drones unaccounted for, the pilots finally clambered into bunkers.

But as soon as the blasts stopped, they rushed back out, now facing a race against time to get their signals up and running so they could find -- and land -- the Gray Eagles.

As dawn started to break, soldiers scrambled to replace 500 metres (yards) of melted fibre cables and reprogramme satellites so they could reconnect to the UAVs.

Last step? Land the "birds."

The Iranian ballistic missiles had punched holes across Ain al-Asad's airfield and the control tower was empty.

"The airfield was shut down so we had to land without talking to anybody. We didn't know where any (other) aircraft was. That part was pretty stressful," said Herwig.

The priority was one Grey Eagle that had been scheduled to land just as the missile attack began, and which stayed flying throughout until it was worryingly low on fuel.

The pilots worked for hours to land each drone one by one, their adrenaline pumping even as other soldiers were recovering, showering and assessing the damage.

At around 9:00 am, the final drone was brought down to earth.

"We landed all our own birds back on site," said Kilpatrick, smiling in relief and pride.

"It was quite a feat."