The bitter rivalry between Boeing Co. and Airbus over supplying tankers for the U.S. Air Force is intensifying at the international air show here, with both sides using sharp-elbowed tactics in the final push to snare a prize worth up to $40 billion, the Wall Street Journal reports.

The two sides have only weeks to make their case before the Air Force makes its choice this fall and have ratcheted up the rhetoric amid indications that military officials might not be inclined to pick a clear winner. The growing fight — which is going beyond the usual sparring over technical nuances or engineering differences — is unusual in the clubby world of defense contracting, where fierce rivals on one project end up working together on the next, and reflects rising concern from both sides that they still have something to prove.

The Paris Air Show provides the last big public platform to win over an audience that includes Air Force Secretary Michael Wynne, as well as senior executives and global media. The military aircraft contract, one of the biggest for the foreseeable future, would replace the Air Force’s aging fleet of aerial tankers, which act like flying fuel depots.

Boeing, the heavy favorite to win the competition, in press conferences at the show has attacked the capabilities of the Airbus A330 that is the center of a proposal submitted by a team led by Northrop Grumman Corp. European Aeronautic Defence & Space Co., which owns Airbus, is Northrop’s partner. Boeing contends the rival plane is too big, uses too much fuel and isn’t designed to be used at some smaller airfields where the U.S. military may need to use it.

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