Days after the Senate voted to confirm him, Ashton Carter took the oath to become the nation’s 25th secretary of defense during a Feb. 17 White House ceremony. A physicist by training, Carter assumes the role as the Pentagon’s top civilian leader after having served as outgoing secretary Chuck Hagel’s deputy for the past two years. In remarks following the ceremony, he promised to focus on helping President Obama make “the best possible decisions about our security,” protect the dignity and well-being of those in uniform, and help forge a path toward a future that ensures national-security goals are met in a fiscally responsible manner.