The good news is that the Pakistan Air Force has finally phased out its 36-year-old U.S.-supplied F-6 aircraft and inducted a fleet of 22 F-7PG jets, newly acquired from China over the past three months. The bad news is that China's F-7 (although much modernized, and beefed up with a MiG-29 engine) is basically a venerable Soviet-era MiG-21 Fishbed, which first flew in 1955. With more than 8,000 produced, the MiG-21 remains by far the most popular combat aircraft of the jet age. China has been producing the F-7 for even longer than the Pakistanis have had the old F-6...