In this March 28, 1999 file photo, Yugoslav army experts check the wreckage of a downed American F-117 aircraft, in the village of Budjanovci, 30 miles northwest of Belgrade. Chinese officials recently unveiled a new, high-tech stealth fighter that could pose a significant threat to American air superiority — and some of its technology, it turns out, may well have come from the U.S. itself. Balkan...