If the U.S. military can ever master technology capable of a boost-phase intercept -- the ability to shoot down enemy intercontinental ballistic missiles immediately after launch -- it will likely be employed in a retaliatory strike because thwarting an initial salvo would come very close to an offensive operation, according to a senior Defense Department official. Missile Defense Agency Director Vice Adm. Jon Hill said the ability to pair a high-energy laser capable of destroying an adversary’s ballistic missile in...