The Air Force (search) continues to order a new type of cargo plane despite spending $2.6 billion to buy 50 planes that do not meet the military's requirements and cannot be flown in combat zones, Pentagon investigators said.

Contractor Lockheed Martin hasn't delivered any C-130J planes (search) that met requirements in the eight years since the program began, the report said. The Air Force and Lockheed Martin disagree.

Problems with the propeller-driven cargo planes include faulty computer and diagnostic systems and inadequate defense measures, the Pentagon's Office of Inspector General concluded.

So far, none of the planes has been cleared for some of their primary missions: Dropping troops and cargo into war zones and flying in conditions requiring the crew to wear night-vision goggles.

The inspector general's report concluded that Air Force and Defense Department officials mismanaged the program, requiring millions of dollars in upgrades and thousands of hours of work to make the planes capable of performing as well as the aging models they're supposed to replace.

The Air Force strongly denied the report's conclusions.

Marvin Sambur (search), the Air Force's top acquisition official, wrote to the investigators that the program is within its cost, schedule and contract guidelines. Lockheed Martin has started delivering planes which meet Air Force specifications and the necessary upgrades have either been completed or scheduled, Sambur wrote.

"While some of the facts presented in the DOD/IG report are accurate, the findings and conclusions ascribed to these facts cannot be supported," Sambur wrote in response to the inspector general's office. "The Air Force fully endorses the C-130J program."

Lockheed Martin spokesman Jeff Rhodes said Friday the company agrees with the Air Force.

"The Air Force, ultimately the end user who is flying the aircraft, also says that the C-130J program is meeting cost, schedule, contract and regulatory commitments," Rhodes said in an e-mail statement.

Two Air Force squadrons haven't been able to perform their missions for more than four years because they only have C-130Js, the report said. The 815th Air Squadron at Keesler Air Force Base in Mississippi and the 135th Airlift Squadron of the Maryland Air National Guard are supposed to drop troops and supplies into hostile areas.

Five other Air Force and Marine units have the C-130J planes but use older C-130s to perform their missions, the report said.

Air Force testers found so many problems with the planes they stopped evaluations in 2000 so the problems they already found could be fixed, the report said.

The report cites problems with the planes including:

--Propellers for C-130Js designed for gathering weather data inside hurricanes were damaged in all tests. The weather planes also didn't have radar strong enough to penetrate storms as far as it should. Upgrades to fix those problems mean C-130Js won't be able to fly hurricane missions until at least next year.

--Diagnostic systems have a high rate of false positives, meaning maintenance crews spend a lot of time trying to repair components which aren't broken.

--The planes did not have an automated system for planning missions.

--The C-130Js are so different from older models that pilots qualified to fly older C-130s must be retrained to fly the new ones.

The Air Force continues to order more C-130Js despite those problems. The military is buying the planes as a commercial item -- a process designed to allow the military to purchase goods on the open market that need few modifications for military use.

That process gives the Air Force less oversight and fewer cost controls, the inspector general's report says. For example, the commercial contract means Lockheed Martin doesn't have to give the Air Force data on how much the planes actually cost, so the Air Force has no way to check the company's profit margins.

Sambur suggested the inspector general's office was biased against such commercial contracts, an accusation the office denied. The inspector general's office has been among critics of another Air Force plan to retrofit Boeing 767 jets for use as midair refueling planes.