The Air Force is paying billions for engine maintenance for the C-17 Globemaster III without any idea if it’s getting a fair price, a new watchdog report said.

“The package will improve the F117 engine’s fuel efficiency, saving up to 6.5 million gallons of fuel annually and reducing CO2 emissions by up to 140 million pounds per year,” P&W says.

The C-17 Globemaster III is one of the larger aircraft deployed by the U.S. Air Force, so it needs a lot of power to operate. Here's who makes the engine.

DoD has subpoenaed Pratt & Whitney's engine unit for the records of more than $1.5 billion worth of maintenance work on C-17s.