In a surprising reversal for the Boeing Company, the Pentagon on Friday awarded a multibillion-dollar contract for refueling tankers to a partnership between Northrop Grumman and EADS, the European parent of Airbus.

The deal, which puts a critical United States military contract into the hands of foreigners, at least in part, calls for spending up to $40 billion on the first phase of a multidecade program to replace the nation’s aging aerial tanker fleet, which dates back to the Kennedy and Eisenhower era. The fleet, which now numbers about 535 refitted Boeing 707’s and DC-10’s is one of the largest but oldest fleets of jets in the world. Yet the tanker planes are essential to keeping Air Force and allied fighter jets, bombers, cargo planes and other military aircraft in the air when on critical missions far from airports where they can land to refuel.

And replacing these tankers  essentially flying gas stations that offload their fuel in mid-air  has been the Air Force’s top priority since 1996, when the government first proposed acquiring new planes. Eventually, the contract is expected to be valued at $100 billion, as the Air Force spends the next several decades acquiring new tankers at a rate of about 15 a year. It is expected that nearly 400 new refueling planes will be needed.

Yet for more than a decade the Air Force’s effort to modernize the fleet has been thwarted by global politics, Washington scandals and an aggressive attack by Senator John McCain, now the presumptive Republican nominee for president.