Those who used to worry endlessly about the “N + 1” problem—rampant proliferation—in the Sixties would be quite surprised some fifty years later. As the consensus of the strategic community had it at the time, there were some twenty countries with the industrial base capable of building nuclear weapons—and would do so in short order.

This past September, the U.S. Air Force introduced a cache of 20 new B61-12 nuclear bombs to the Luftwaffe’s Büchel Air Base in western Germany. The upgrade, part of the NATO program on nuclear “sharing,” replaced a higher-yield version of the venerable B61 with a less destructive weapon, but it nonetheless sparked protest by opposition parties in Germany.

American thinking about missile defense has been incoherent from the very beginning. The issue is superficially simple: the Soviet Union threatened the American people with nuclear missiles, so the U.S. should naturally have tried to defend them against those missiles.

A new era of modern warfare began when German V-2 missiles hit London in September 1944. Within the next few years, the U.S. military was issuing reports on how to proceed in the development of defensive counters to ballistic missiles.