The Pentagon wasted as much as $100 million on commercial airplane tickets that were never used between 1997 and 2003, according to a new report by the investigative arm of Congress, due to be released Wednesday. NBC News obtained an advance copy.

Congressional critics who initiated the probe call it an appalling level of waste. 

According to Rep. Jan Schakowsky, D-Ill., “This is the time for the Department of Defense to get a grip. If we are at war and we have troops in the field that don’t even have adequate equipment, then we can’t afford to have money slipping through our fingers just because we are not paying attention.”

How could it happen? The report identifies “control breakdowns” in Pentagon accounting and “a flawed process” that relied on Department of Defense personnel to report their own unused tickets.

The report says the Pentagon didn’t even know there was a problem.

Sen. Chuck Grassley, R-Iowa, said, “Isn’t it ridiculous that you can have a hundred million go up in smoke in the Defense Department without anybody in the Defense Department knowing about it?”

A government watchdog says this is just the latest in a series of reports identifying Pentagon waste. One report even found Department of Defense credit cards used for everything from breast implants to shopping sprees.

“What I find astounding is that there seems to be no accountability, there seems to be no one that gets in trouble when these things happen,” said Eric Miller of the Project on Government Oversight.

The Pentagon declined to respond on camera but issued a written statement saying, in part, “We take this deficiency in our procedures very seriously and are moving swiftly to establish proper management controls.”

Not all of the money the Pentagon spent on canceled tickets is gone forever. Some of it is still refundable and the Pentagon says it will now begin the process of trying to get some of it back.