The United Kingdom will buy 12 U.S.-made F-35A fighter jets capable of carrying nuclear bombs and will join NATO’s shared airborne nuclear mission, in a major expansion of its nuclear deterrent, Prime Minister Keir Starmer announced Wednesday. The government called it “the biggest strengthening of the U.K.’s nuclear posture in a generation.” Starmer made the announcement while attending a NATO summit in the Netherlands. NATO Secretary-General Mark Rutte welcomed the decision, calling it “yet another robust British contribution to NATO.” The U.K. phased out air-dropped atomic weapons in the 1990s after the end of the Cold War. Its nuclear arsenal...