President Barack Obama on Friday nominated former Deputy Defense Secretary Ashton Carter to replace outgoing Defense Secretary Chuck Hagel.
Obama said Carter is regarded "as one of our nation's foremost national security leaders."
"He knows the Department of Defense inside and out," Obama said. "On Day One, he's going to hit the ground running."
Carter said he "discussed the challenges and opportunities" of the role with Obama before accepting the nomination. He said he accepted the role in part because of the respect he and his wife Stephanie have for the troops.
"I pledge to you my most candid, strategic advice, and I pledge to you, you will receive equally candidate military advice," Carter said.
Obama noted Carter has served under both Republican and Democratic secretaries of defense and is respected by lawmakers on both sides of the aisle. He also praised Carter's "true regard, his love" for the troops. Obama said he suspected Carter's confirmation by the Senate "would happen very quickly."
Obama also referenced Carter's previous stint in the Defense Department in his nomination speech.
"In your one-year attempt at retirement for public service, you failed miserably," Obama said.
Obama also joked about a fake Twitter account impersonating Carter that sent a tweet about his nomination earlier this week.
"I know some people think I announce Cabinet positions on fake Twitter accounts; this is not the case," Obama said.
Hagel announced in late November he would step down from his job as Secretary of Defense, saying it was "the greatest privilege of my life to lead and, most important, to serve with the men and women of the Defense Department and support their families."
Hagel praised Carter in 2013, saying he had an "unparalleled knowledge of every facet" of the U.S. defense system. Hagel did not attend Carter's nomination ceremony on Friday.
Carter, a Rhodes scholar and physicist, has a background in policy and has served under 11 defense secretaries. He will be the fourth defense secretary to serve in the Obama administration, following Hagel, Leon Panetta and Robert Gates.
NBC reports Carter has the support of top Republicans in the Senate, which could lead to an easy confirmation. Amid reports that Carter was chosen as the nominee for secretary of defense, Sen. Jim Inhofe (R-Okla.) said he would be "very pleased" at the choice.
"I can't imagine that he's going to have opposition to his confirmation," Inhofe said.
The AP reported earlier on what may be in store for Carter as defense secretary:
Defense analyst Anthony Cordesman said that as Obama approaches the end of his presidency, the Cabinet post is "not particularly desirable" for anyone with broader political ambitions.
"It's very unlikely you will get political visibility or credit for being the secretary," said Cordesman, who works at the Center for Strategic and International Studies. "There are just too many problems and uncertainties."
Among them: questions about the effectiveness of Obama's military campaign against the Islamic State in Iraq and Syria, Russia's continued provocations in Ukraine, tensions between the White House and Defense Department over closing the Guantanamo Bay detention center, and concerns at the Pentagon with the impact of deep spending cuts.