LONDON (AP) — When an Icelandic volcano erupted last week, it didn't just wreak havoc with commercial flights. It grounded American jet fighters and some of the most advanced air forces in the world.

Like their commercial cousins, fighters, reconnaissance planes, helicopters and other military aircraft around the region sat idle for days. They are just now beginning to come back to life, although fighter jets — which have highly sensitive engines — remain grounded across much of Europe.

The U.S. Air Force's biggest fighter wing in Europe, at England's RAF Lakenheath air base, was under no-fly orders and many of its F-15s were being kept in protective shelters. U.S. military officials at their European headquarters in Germany said they were keeping all aircraft on routine missions on the ground regionwide as a precaution.

At Aviano Air Base in northern Italy, "when everyone else wasn't flying, we weren't flying either" during the airspace shutdown, said U.S. Air Force Lt. Kim Schaerdel.

But some F-16s started flying on Tuesday evening, and by Wednesday operations were "back up at full steam" at Aviano, with inspections showing the ash cloud had caused no damage, said base colleage Lt. Brian Wagner of the 31st Fighter Wing.

Fighters are more susceptible to the ash in part because their engines operate at higher temperatures due to more extreme performance requirements, making it more likely that the ash will melt inside the engine's hot parts.

Col. John Quintas, the 48th Fighter Wing operations group commander at Lakenheath, said extensive tests were to be conducted on the engines of two fighters that were set to fly later Wednesday. More flights would be allowed only if no damage is found.

"We're evaluating the situation, looking at the weather patterns and trying to make the determination when it would be acceptable to resume our training operations," said Lt. Col. Dave Honchul at Ramstein air base in Germany. He said that through Wednesday about 300 training missions for all their planes had been canceled.

Qunintas said the military was under less pressure to get back in the air immediately than commercial operators.

"Our mission is training to be combat ready, and they are losing dollars by the minute," he said. "The directors of commercial airlines are under a lot more stress. I can afford to be on their heels and let them assume a little of the risk."

But he said the volcano has clearly affected the military's ability to carry out its mission, and could continue to do so in the months ahead.

"Anytime you have a reduction of operations you are atrophying the training of your aviators," he said. "You have to be cautious about how to get back into high performance."

Getting supplies to Afghanistan has also gotten more complicated, and troops have had to deal with mail not being delivered properly and low supplies at base stores.

Two US military bases in southern Spain are seeing big increases in stopovers by transport planes heading to or from Afghanistan because the planes can no longer stop over in Germany for refueling or maintenance, meaning longer flying times and delays. Medical flights to Landstuhl Regional Medical Center near Ramstein for troops injured in Afghanistan and Iraq have been halted although hospitals in the war zones are not short of supplies or overwhelmed by patients, said spokeswoman Marie Shaw.

"We haven't had any patient arrivals or departures," she told The Associated Press Wednesday. "We hope now that the airspace is open we are going to be able to move some people."

To test the safety of the skies, some fighter jets flew during the closure period. Not all came back unscathed — one Belgian F-16 and two Finnish F-18s reportedly had engine damage after flying through the ash cloud, an outcome that could bode ill for future fighter operations if the volcano continues to belch ash.

Even with fighters out of the air for the time being, military officials said their overall air defenses — which rely heavily on ground-based radar systems, not on airborne fighters — are not significantly compromised.

NATO took the precaution of transferring several of its Boeing E-3A aerial early-warning radar planes from their base in Germany to Italy last week ahead of the main ash cloud to retain surveillance flights deemed crucial for European air defense. The four-engine jets continued their high-altitude patrols throughout the ash emergency, officials said.

Col. Greg Julian, spokesman for the alliance's supreme military headquarters in Mons, Belgium, said NATO was able to shift many operations involving logistics, medical flights, surveillance and air defense. Hubs in southern Italy and Spain were pulled into use, he said.


AP reporters Matt Moore in Berlin, Pauline Jelinek in Washington, Slobodan Lekic in Brussels and Frances D'Emilio in Rome contributed to this report.