The aircraft arrayed around the spacious lawn of Maxwell Air Force Base, home of the Air University, mostly represent long-retired types. The largest, however, is a glistening B-52 bomber, which represents a still-employed component of the U.S. Air Force's aging fleet: The youngest B-52 entered service in 1962. Sons have flown the same plane their fathers and grandfathers flew.

But, then, the average age of all the U.S. Air Force aircraft is 27 years; fighters, more than 30 years; bombers and helicopters, more than 40 years; refueling tankers more than 50 years. America's security challenges change much faster — think of the Soviet Union's demise and the Islamic State group's rise — than new technologies can be conceived, designed, approved, built and deployed. The F/A-18 and the F-16 were designed about 45 years ago.

On April 15, 1953, two U.S. soldiers in Korea were attacked and killed by a propeller-driven aircraft supporting Chinese and North Korean troops. Since then, no U.S. ground troops have been attacked by an enemy aircraft. Such has been the permissive environment guaranteed by U.S. air dominance, not since Vietnam has a U.S. pilot used his aircraft's bullets to down an enemy fighter plane (although air-to-air missiles downed enemy aircraft over the Balkans).