WASHINGTON (CNN) -- Once derided as a white elephant, the U.S. Marine Corps' tilt-rotor aircraft, the V-22 Osprey, is proving its mettle in Iraq, military officials said.

An Osprey refuels before a night mission last week in central Iraq.

The Osprey, which takes off and lands like a helicopter but flies like a plane, was designed to replace the Corps' aging and less-capable helicopter fleet.

But a series of accidents involving the planes left 30 people dead from 1991 to 2000, and critics said the Osprey never would be able to replace the Vietnam-era CH-46 Sea Knight, which was the Corps' airlift workhorse.

The military, which has ordered 360 of the aircraft, said the 10 deployed to Iraq are doing what they are supposed to do -- carrying troops faster, farther and safer than the copters can.

Last September, Marine Medium Tiltrotor Squadron 263 left for Iraq's western Anbar province on the first deployment of the V-22.

Since then, the planes have logged more than 2,000 flight hours, initially doing routine cargo and troop movements from base to base in an area about the size of South Carolina.

In December, commanders gave the planes a more risky mission called "aero-scout" in which a group of V-22s flies into a relatively unsecured location and drops off Marines for a search mission.

The planes sit on the ground until the Marines load up and then fly off to somewhere else for another mission.

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The Osprey's speed has been a lifesaver, too, squadron officials said.

For instance, they said two V-22s were dispatched to fly a more than 130-mile round trip in the remote western desert to pick up a wounded Marine and get him to a hospital. The planes were able to do so in an hour, something no helicopter in the Marine inventory could do, squadron officials said.

Commanders in Iraq have allowed little media coverage of the V-22s since their arrival, wanting to get crews used to their mission and to keep insurgents from targeting the planes for propaganda purposes. The planes have not come under direct fire, officials said.

Critics said the plane is lightly defended, with only one rear-mounted gun.

But Marines said the Osprey has enough power and speed to get out of a hostile zone faster than any helicopter, and the aircraft can fly higher, allowing it to be out of range of shoulder-fired missiles.

The Osprey seems to have become a favorite of commanders who need to get to places quickly, including Gen. David Petraeus, the top U.S. military commander in Iraq. Petraeus used one to fly around the country on Christmas Day to visit troops.

"Gen. Petraeus flew in the jump seat and was very impressed by the aircraft's capabilities," according to Col. Steve Boylan, a spokesman for the general.

"The rate of climb is exceptional, and it can fly about twice as fast as a Black Hawk [helicopter], without needing to refuel as frequently," Boylan said. "Beyond that, its automatic-hover capability for use in landing in very dusty conditions, even at night, is tremendous."

Petraeus chose the Osprey for that mission because it was the only aircraft in the inventory that could fly around the country without refueling and not rely on runways, Boylan said.

Despite glowing remarks from troops in Iraq, the planes have an overarching reliability problem, according to critics.

"The Marines will tell you it's a new plane, and all new aircraft have problems, but it's not a new plane; it's been around for a long time now," said Philip Coyle, former chief of the Pentagon's weapons testing division.

"It seems like every time one problem is fixed another one comes along, and I just don't think the program will be able to get over that."

Marines contend the planes have performed well, with six to eight aircraft out of 10 available at any one time.

No serious reports of mechanical problems have been reported with the planes in Iraq, according to Marine Corps officials in Washington, and a shortage of spare parts has been alleviated.

Critics such as Coyle said they aren't convinced the planes are the answer for the Marines.

"It has flown more than 2,000 hours in Iraq, but most of that has been carefully coordinated to minimize the risks," he said.

"The program is like a bad poker hand. They keep putting money into it when they should have spent it on a new helicopter system."

The Marine commands in Washington and Iraq said they do not let the critics faze them.

"As with any first-time deployment, new lessons are learned every day," one Marine deployed with the Osprey squadron said. E-mail to a friend

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