January 26, 2013: With continued delays in the arrival of the F-35 fighter, the U.S. Air Force is spending nearly $6 billion to upgrade and refurbish its F-15s. Most of this money is going into upgrades for its 220 F-15E fighter bombers. Between 2008 and 2017, some $3 billion will be spent on the F-15Es, mainly for new electronics.

Most of the remaining money is being spent on 400 older F-15s, some of which have flown over 10,000 hour so far. The F-15 was originally designed to last only 8,000 hours. But since it was introduced over 30 years ago, there have been many improvements to the air frame and the air force is hoping to get 18,000 hours out of most of the older F-15s.