President Barack Obama named Dr. Ashton B. Carter as his choice to become the 25th secretary of defense on Dec. 5.In one way or another, Obama said at the White House ceremony, Carter has served 11 secretaries of defense."He’s an innovator who helped create the program that has dismantled weapons of mass destruction around the world and reduced the threat of nuclear terrorism," Obama said."He’s a reformer who’s never been afraid to cancel old or inefficient weapons programs; he knows the Department of Defense inside and out. All of which means that on day one, he’s going to hit the ground running," he noted.Defense Secretary Chuck Hagel said in a statement issued earlier that he supports Carter’s nomination.On Nov. 24, the president accepted Hagel’s resignation as defense secretary. Hagel has agreed to stay on until his successor has been confirmed by the U.S. Senate.Strategist, scientist, scholarCarter, Hagel said, has held the No. 2 and No. 3 jobs at the Pentagon and for both was confirmed unanimously by the U.S. Senate."He is a renowned strategist, scientist and scholar with expertise spanning international security and counterterrorism to science, technology and innovation," Hagel added, "and I know that Ash and [his wife] Stephanie are committed to America’s men and women in uniform and their families."Carter said he accepted the president’s nomination "because of my regard for his leadership [and] because of the seriousness of the strategic challenges we face, but also the bright opportunities that exist for America if we can come together to grab hold of them."He also accepted the nomination, he said, because of the deep respect and abiding love that he and his wife Stephanie have for the men and women in uniform.Pledging candid adviceCarter said that if confirmed he would give the president his most candid strategic and military advice."And finally," Carter added, "to the greatest fighting force the world has ever known, to you I pledge to keep faith with you and to serve our nation with the same unflinching dedication that you demonstrate every day."Carter served as deputy defense secretary from Oct. 2011 to Dec. 2013 under former Defense Secretary Leon E. Panetta, and later under Defense Secretary Chuck Hagel.Under Hagel, Carter’s portfolios included serving as the department’s point man in defense relations with India and heading the department’s investigation into the September 2013 Washington Navy Yard shooting that killed 12 people and injured three others.Leading DoD acquisition effortsAs under secretary of defense for acquisition, technology and logistics from April 2009 to Oct. 2011, Carter led DoD efforts to speed the fielding of urgently needed equipment, including mine-resistant, ambush-protected vehicles.He also worked to increase Pentagon buying power and helped bolster U.S. defenses against emerging threats.Over the course of his career in public service, Carter four times received the DoD Distinguished Service Medal. For contributions to intelligence, Carter received the Defense Intelligence Medal.Over the years Carter has moved several times between academia and government, and a 2007 autobiography written while he was on the faculty of Harvard University’s John F. Kennedy School of Government describes a career transition that began in theoretical physics and moved into defense and international security.He earned bachelor’s degrees in physics and in medieval history from Yale University and received his doctorate in theoretical physics from Oxford University, where he was a Rhodes Scholar.From physics to international securityAfter his study at Oxford, Carter returned to the United States to begin climbing the academic ladder in physics, he said in the autobiography.In 1979 colleagues convinced him to take a yearlong leave of absence from theoretical physics to join a study team of scientists at the Congressional Office of Technology Assessment.The team was asked to analyze all the ways MX intercontinental ballistic missiles could be protected from a Soviet Union nuclear first strike.The experience left him with a deep concern about the problems of international security, he said, and he decided to change careers.His first job at the Pentagon was in the systems analysis department in the Office of the Secretary of Defense."My job covered strategic nuclear forces, strategic defenses including missile defenses, space and intelligence systems, command-and-control systems and nuclear weapons," Carter said.Enjoying the job"I could easily understand these technologies and some of the policy issues that arose," he said, adding that he enjoyed the job and liked working at "what we denizens of the Pentagon all jokingly called ground zero."Later, during the Clinton administration, Carter served as assistant secretary of defense for international security policy.Before joining the Obama administration, Carter chaired the International and Global Affairs faculty at Harvard University’s John F. Kennedy School of Government and co-directed the Preventive Defense Project.No shortage of security challengesAt the White House, Obama said the nation faces no shortage of challenges to national security."Our combat mission in Afghanistan ends this month and we have to transition to a new mission of advising and assisting Afghan forces and going after remnants of al Qaeda’s core," the president said.Adding, "We have to keep degrading and ultimately destroying [the Islamic State in the Levant] in Iraq and Syria. We have to build counterterrorism partnerships and new platforms. We have to continue the fight against Ebola in West Africa. We have to continue to strengthen our alliances, including NATO, and continue rebalancing our defense posture in the Asia-Pacific."Obama also said the nation needs a leaner military and that as commander in chief he would make sure it remains second to none.Making smart choices"Ash is going to be critical to all these efforts," Obama added."When we talked about this job we talked about how we’re going to have to make smart choices … [and] squeeze everything we have out of the resources we have to be as effective as possible. And I can’t think of somebody who’s more qualified to do that" than Ash Carter, he added.