President-elect Joe Biden nominated Kathleen Hicks to be deputy secretary of defense, making her the first woman to hold the number two position in the Pentagon, if she is confirmed by the Senate.
Ms Hicks, who is heading Biden's transition team at the Pentagon, served in the Defense Department under former president Barack Obama, including as deputy undersecretary of defense for strategy, plans, and forces.
She is currently at the Center for Strategic and International Studies think tank in Washington.
CSIS President and CEO John J. Hamre said Ms Hicks will flourish in the role.
"I held that job and know what it takes to succeed. Dr. Hicks is a superb choice for this important job. She has the discipline, intellect, and organizational skill to make the Department work effectively for the Secretary.
"She has a strong moral compass and a keen commitment to the success of the Department and the well-being of its military and civilian personnel. I am very pleased that President-elect Biden has selected her."
In a message posted on Twitter, Ms Hicks said she would welcome the opportunity to work with Joe Biden and Kamala Harris.
Mr Biden, who takes office on January 20, also named another civilian, Colin Kahl, who also served in the Obama administration, to a senior Pentagon post.
Mr Kahl was nominated to be undersecretary of defense for policy.
"They know the Pentagon inside and out and are well-positioned to take on the full sweep of challenges facing our armed forces," Biden said in a statement, including "restoring our alliances."
Mr Biden has nominated a retired general, Lloyd Austin, to be defense secretary.
Another woman, Christine Fox, served as acting deputy secretary of defense for six months under Obama until her retirement in 2014 but she was not put up for Senate confirmation.
