Ashton B. Carter officially became the 25th U.S. secretary of defense on Tuesday, taking the oath of office at the White House in a ceremony with Vice President Biden.

Carter, standing next to his wife, Stephanie, took the oath of office in the Roosevelt Room at the White House. He said that becoming secretary of defense was the “highest honor,” and he thanked his wife, two children and others who have helped him prepare for the job.

“I am honored to rejoin the men and women of the Defense Department in what is the highest calling, which is the defense of our country,” he said.

Carter has served previously in senior posts at the Pentagon, including as its No. 2 leader from October 2011 to December 2013. He was characterized by Biden as a “profoundly capable manager” who has a long record of negotiating Washington’s bureaucracy to rush equipment needed by U.S. troops into the field.

“This man has a driving intellectual force behind all he does, and all that this administration has been doing,” Biden said.

Biden cited Carter’s role in rushing 24,000 mine-resistant vehicles to Iraq and Afghanistan. Not everyone on Capitol Hill or the Pentagon was in favor of spending the more than $20 billion the effort required, but Carter helped shepherd the project against skepticism, the vice president said.

“Ash, your pioneering work is what saved thousands of lives and limbs in the process,” Biden said. “If you did nothing else in your career, that was a pretty important thing to have done.”

Carter said he is making three commitments as he takes his new job: To ensure President Obama has the best information available as he makes national security decisions and to carry them out afterward; to protect U.S. troops, their dignity and their well-being; and to build a capable force ready for future challenges.

In a message released to all U.S. troops and Defense Department employees shortly after the ceremony, he outlined some of the threats the United States faces.

“We confront a turbulent and dangerous world: continuing turmoil in the Middle East and North Africa, and the malignant and savage terrorism emanating from it; an ongoing conflict in Afghanistan; a reversion to archaic security thinking in parts of Europe; tensions in the Asia-Pacific; the proliferation of weapons of mass destruction; and intensifying threats in cyberspace,” he wrote, in part.

Carter’s first morning as Pentagon chief included meeting with Deputy Defense Secretary Robert Work, Army Secretary John McHugh, Navy Secretary Ray Mabus and Air Force Secretary Deborah James, according to a senior defense official. Carter was expected to meet with Obama privately in the Oval Office on Tuesday afternoon.

“He comes prepared to make tough decisions to defend the country and support the men and women of the Department, while at the same time embracing change and building the force of the future,” the senior defense official said.