WASHINGTON — In taking a deep look at trouble inside U.S. nuclear forces, Defense Secretary Chuck Hagel is searching for the root causes of recent Air Force missteps but also for ways to make the nuclear warrior’s job more attractive at a time when the military has turned its attention away from such weapons.

Nuclear missile duty has lost its luster in an era dominated by other security threats. It’s rarely the career path of first choice for young officers. And yet Hagel and others say it remains important to U.S. national security.