A Boeing-led team has finished building 20 new silos for the homeland missile defense system at Fort Greely, Alaska, growing the number of interceptors that can be emplaced there from 40 to 60.

In 1963, the United States armed 54 missile silos with launchable nuclear bombs, which could travel some 6,000 miles each and kill millions of people, flash-blind hundreds of thousands and leave a ...