KABUL (AFP) - A freak hailstorm in Afghanistan damaged more than 80 US military helicopters, wrecking rotor blades, shattering windows and grounding aircraft for weeks until repairs were completed, the army said on Thursday.

Golf ball-sized hail stones struck Kandahar airfield on April 23, triggering an emergency operation to get the helicopters back in the air in one of the most violent hotspots of the Taliban insurgency.

The US military described how the "sudden unprecedented hailstorm" had badly dented the sheet metal skins of the helicopters, which were parked outside at the airfield in the desert-landscape of southern Afghanistan.

"The sheer number of airframe repairs required after the hailstorm provided five years worth of experience for the airframe mechanics," a press release said, adding the helicopters were needed as the Afghan "fighting season" was underway.

About eight of the helicopters were still not airworthy after three weeks of intense repair work, which included having new rotor blades and canopies flown in from Kuwait.

The Afghan national army is taking over the fight against the Taliban, but the US continues to provide almost all air support.

"The enemy had no opportunity to take advantage of the impact on our aircraft," said Colonel Allan Pepin, commander of Task Force Falcon, 3rd Combat Aviation Brigade.