Our AWACS is getting a littld long in tooth. The U.S. Air Force E-3 inventory was built with used Boeing 707s (though some allies are buying a 767 version) for the airframes, and even with a number of updates, are due for replacement. This high altitude surveillance system covered in the January 2007 Popular Mechanics is one of the more unique concepts under consideration to replace or supplement the E-3.

Hat tip to Glen Reynolds.