ASAD AIR BASE, Iraq — After a troubled history, the V-22 Osprey — half-helicopter, half-plane — has been ferrying troops and equipment across Iraq for just over a year without a major incident.

Critics say the Osprey, which was designed to replace transport helicopters, lacks firepower for defense in heavy combat.

But pilots say the Osprey makes up for that in speed, which one of them says can take the plane "like a bat out of hell" to altitudes safe from small-arms fire.

Since arriving at this sprawling desert base in western Iraq, a dozen Ospreys have been ferrying troops and equipment at forward operating bases. One even took around Barack Obama during his tour of Iraq earlier this year.

But on only a handful of occasions has the aircraft faced any serious enemy fire.

Military officials say this is partly a result of the changing nature of the war in Iraq as well as the advantages the high-flying Osprey has over the Vietnam-era Sea Knight helicopters it will eventually replace. The Osprey has also avoided day flights into Baghdad or other tasks that entail high risk.

"It's not the same World War II tactics that we used to deal with, or even Vietnam tactics," said Maj. Paul Kopacz, who led two Ospreys on a recent mission to Fallujah. "We have not been battle-tested because we aren't going guns blazing into hot zones. Our nation is now too sensitive to the loss of soldiers to let that happen."

The military calls the Osprey a "tilt-rotor" aircraft, because it takes off with its rotors set vertically like a helicopter, then flies with them thrust forward as on an airplane. The shift requires only a pull of a lever by the pilot.

The aircraft, which took more than two decades to develop, has been plagued by a series of technical failures and deadly crashes — including a pair in quick succession in 2000 that killed 23 Marines and nearly scuttled the entire project.

Some skeptics have criticized the design as making the plane too slow in descent, lacking in maneuverability and kicking up too much dust and they say it should have been delayed until designers mastered "autorotation" — which would keep the rotors spinning even if both engines are taken out.

Another issue has been the lack of firepower on the Osprey, which does not include a mounted gun on the front as once envisaged — although the Marines have placed a machine gun at the rear.

There are also the aircraft's soaring costs, which have pushed the bill to more than $100 million per unit including research and development expenses.

Still, the aircraft has won wide support from Marines flying it in Iraq since September 2007, even among those with long experience as pilots of the CH-46 Sea Knight. They say the problems experienced so far have been caused by desert dust and heat, mostly related to avionics and nothing that has overly confounded technicians.

"I used to fly the CH-46 and we couldn't do nearly what we do now in terms of weight, cargo, distance or speed," said Lt. Col. Christopher Seymour, commanding officer of what is now the third Osprey squadron at Asad air base, a complex in the desert of western Iraq that houses 10,000 U.S. servicemen.

Seymour and the other pilots at Asad say they've noticed the Osprey's advantages. It can travel twice as fast and three times farther than the Sea Knight, is equipped with radar, lasers and a missile defense system, and soars at altitudes far above its 39-year-old predecessor.

"It's a gorilla. The ability to accelerate to speeds is so strong," Seymour said, adding that the Osprey's benefits will become even more evident as the military continues to move away from ground convoys, which face roadside bombs and ambushes. "Like a bat out of hell you're at altitudes safe from small-arms fire."