Sept. 19, 2011  -- America's F-22 Raptor, the world's most advanced and expensive stealth jet fighter, will be heading back into the skies to protect the homeland after a nearly five-month grounding due to oxygen problems, the Air Force announced today.

The entire fleet of F-22s -- over 160 planes -- has been waiting on the tarmac since early May after the Air Force reported 12 separate incidents of pilots experiencing "hypoxia-like symptoms" in the past three years while flying the planes.

The planes will slowly make their way back between the clouds in a "comprehensive incremental return-to-fly plan" after the entire fleet undergoes an "extensive inspection of the life support systems," the Air Force said. The planes were grounded so long that the pilots reportedly may have to repeat grueling training just to become proficient in the complex planes once again.

"We now have enough insight from recent studies and investigations that a return to flight is prudent and appropriate," Air Force Chief of Staff Gen. Norton Schwartz said in a statement. "We're managing the risks with our aircrews, and we're continuing to study the F-22's oxygen systems and collect data to improve its performance."

The first of the F-22s are scheduled to hit the skies Wednesday, the Air Force said. But going back into the air does not mean they will be heading back into combat.

Despite being operational since December 2005, the F-22 has not been an "operational requirement" in any major theater of combat for the U.S., from Iraq to Afghanistan or Libya, the Air Force said.

READ: The $77 Billion Fighter Jets That Have Never Gone to War

Not a single one of the planes -- which cost U.S. government $77.4 billion for a total of 187 planes from developer Lockheed Martin, according to a report by the Government Accountability Office -- has used what Lockheed Martin's website called a "revolutionary leap in lethality" in defense of U.S. interests abroad and isn't expected to "any time soon," an Air Force official told ABC News.

The planes have, however, flown more than 300 missions in support of Operation Noble Eagle -- a series of military operations directed at homeland defense and civil support, according to the Department of Defense.

The Pentagon initially ordered more than 600 of the fifth-generation fighters, but Congress stopped at funding 187 in 2009 under a hail of criticism over the fact that the planes are designed to take on other rival high-tech fighter jets -- jets that did not exist at the time.

Only recently have rival major powers -- including Russia and China -- unveiled their prototypes for what are believed to be their own stealth fighters, supposedly capable to taking on the F-22.

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