In the shadow of their better-known Army and Navy counterparts, Air Force (search) commandos have been sent into Iraq and Afghanistan so frequently that strains are showing in many corners of their secretive world.

Wear and tear on their specialized helicopters and airplanes is mounting, as is the human toll in lives lost and families separated. Spare parts are in such demand for special operations aircraft now seeing action that those remaining at Hurlburt are not fully ready for training.

"We're wearing 'em down," says Lt. Col. Don Timpson of the 19th Special Operations Squadron, which trains air crews. He was referring to pilots who fly the AC-130 gunships, MC-130 Combat Talon airlifters and other specialized airplanes and helicopters that require extensive training.

Their planes are equipped with radar and electronic gear to enable them to penetrate enemy airspace undetected at night as well as guns and cannons capable of exceptionally heavy fire on a target.

Timpson and other officers are using flight simulators much more to train new pilots and keep veterans proficient because they sometimes cannot practice in the air for lack of planes.

At their Hurlburt Field headquarters on Santa Rosa Sound, in Florida's Panhandle, air commandos point with pride to the furious pace of their service in the war on terror since the Sept. 11, 2001, attacks.

"We are going just full throttle" to get additional air commandos trained, said Col. Thomas Hull, vice director of operations for Air Force Special Operations Command.

One unit, the 8th Special Operations Squadron, was the most-deployed squadron in the entire active-duty Air Force in 2002 and 2003. It flies the MC-130E Combat Talon I, now in its fifth decade of use to deliver and retrieve forces behind enemy lines.

Likewise, elements of the 20th Special Operations Squadron, which flies the MH-53J Pave Low helicopter, have been serving in Afghanistan (search) and Iraq almost continuously since September 2001. Finally getting a six-month break, all members of the unit were home together for the first time last Christmas. Now some are back in Iraq for another tour.

Smaller in number than the Army's Green Berets and less glamorized than the Navy's SEALs, the Air Force's 12,000 special operations airmen are rarely mentioned publicly for their contributions during the invasions of Iraq (search) and Afghanistan and the hunt for terrorists.

Their specific missions, often classified secret, fall generally into five categories:

— Training and advising foreign air forces, for which they have extensive language study.

— Providing secret airlift of troops and supplies through hostile or politically sensitive air space, as they did in the initial stages of the Afghanistan and Iraq invasions.

— Aerial refueling of special operations aircraft and helicopters. An Air Force Reserve unit, the 919th Special Operations Wing, was in such demand for helicopter refueling during 2001-03 that it was mobilized for 24 months — the maximum allowed.

— Providing close-air support of ground forces with AC-130 gunships, packed with a unique combination of firepower, including a side-shooting cannon that fires 105mm shells that weigh 33 pounds each.

— Assisting other ground forces, mainly with "special tactics" commandos, to scout potential landing zones, identify small or mobile ground targets for air attack, manage air traffic and provide weather data. They include an elite medical force called the pararescue jumpers, who are trained to parachute or jump from helicopters to save downed air crews.

One such unit, the 24th Special Tactics Squadron, is among secretive "special mission units," including the Army's Delta Force and the Navy's SEAL Team 6, used for counterterrorism and other secret operations not publicly acknowledged by the government.

Much of their work is classified. But they were featured in 2001 photos showing U.S. troops riding horseback with Afghan fighters in northern Afghanistan as they located targets for airstrikes against the Taliban. And Air Force commandos were among the first U.S. troops to cross into Iraq at the start of the war in 2003, to set up refueling and rearming points in remote areas.

Chief Master Sgt. Jim Mowry, the senior adviser to the Air Force Special Operations commander on issues involving enlisted airmen, says the past 3 1/2 years have been the busiest for air commandos in decades. He sees no significant drop in morale among his troops.

"Morale as a whole is very, very high, and that kind of surprises me for a number of reasons, primarily because we are working our folks really hard and some of them have been on multiple deployments with little time (off) in between," Mowry said.

Hull, the vice director of operations, said that while the command remains busy, the pace has slackened from two years ago, when the demands of an Iraq invasion were added to a heavy workload in Afghanistan.

"We were nearly tapped out" of wartime resources at that point, he said. "That was pretty near the whole shootin' match. Then what we ended up having to do is kind of regroup and draw back and say, `What is it we can sustain?'"

In recent months the command has worked out a unit rotation so airmen and their families know a year in advance when they will go overseas.

As a re-enlistment incentive to the most experienced air commandos, the Pentagon is offering bonuses for certain "critical skills" of up to $150,000 for a six-year re-enlistment.