Northrop Grumman is/was a major U.S. defense contractor which built the B-2 Spirit stealth bomber. And the tanker conversion phase jobs will be based in Alabama, so this award will still create a lot of U.S. jobs (although probably not as many as a Boeing award would have). There are many different angles that the USAF could have considered in awarding the deal to Northrop-EADS:
..1.. With Lockheed and Boeing being the only two active aircraft airframe manufacturers remaining in the States, the USAF probably wanted to make sure Northrop had enough business to remain a viable future manufacturer...
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(From Wikipedia) Northrop Grumman intends to bid for the U.S. Air Force's next-generation strategic bomber project. Though it has not built a large manned aircraft since wrapping up B-2 Spirit production in the 1990s, the company has "been working hard to turn that perception around, with the skills and capabilities that back it up."
Northrop Grumman partnered with EADS to use the KC-30 to win U.S. Air Force's KC-X tanker competition. Northrop Grumman/EADS will be required to invest approximately US$600 million in a new assembly plant in the United States, which is currently planned for Mobile, Alabama. On February 29, 2008, the US Air Force chose the Northrop Grumman/EADS's KC-30.
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..2.. Just as the Boeing 787 will depend upon foreign manufacturers (without which the 787 won't fly), the mammoth USAF F-35 fighter program is also dependent on foreign contractors (e.g. BAE/British Aerospace) and on foreign government purchases for its success. The Air Force may have figured that this was a good way to earn some reciprocal goodwill.
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(From Wikipedia) While the United States is the primary customer and financial backer, the United Kingdom, Italy, the Netherlands, Canada, Norway, Denmark, Australia and Turkey have contributed US$4.375 billion toward the development costs of the program. Total development costs are estimated at more than US$40 billion (underwritten largely by the United States), while the purchase of an estimated 2,400 planes is expected to cost an additional US$200 billion. The nine major partner nations plan to acquire over 3,100 F-35s through 2035, making the F-35 one of the most numerous jet fighters.
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..3.. The USAF (presumably) concluded that the Northrop-EADS deal was simply the better (more capable, more cost-effective) deal for itself and that the Boeing deal was inferior after the scoring was all said and done.
..4.. The previous ethics scandal with Boeing may have caused Air Force acquisition officials to put Boeing in the penalty box for a while. Boeing's previous no-bid tanker deal with the Air Force (while simultaneously offering a plum job to the AF official negotiating on behalf of the government) was one of the worst and most egregious violations of government-contractor ethics in recent years.
I'm definitely interested in learning about the USAF's selection criteria and scoring methodology, but in retrospect they seem to have made a good although politically bold choice.