WASHINGTON The Marine Corps is now without a Senate-confirmed leader for the first time in over a century thanks to a Republican senator's block on military nominations.

Retiring Gen. David Berger formally relinquished command on Monday as the Marine Corps' commandant, creating the first of several possible vacancies of Senate confirmed leaders on the U.S. military's Joint Chiefs of Staff in the coming months.

Republican Senator Tommy Tuberville, who represents Alabama, has blocked hundreds of military nominations from moving forward because he believes the Pentagon is improperly using government funding to cover travel costs for abortions for service members and their dependents.

U.S. Defense Secretary Lloyd Austin denounced the delay at Berger's retirement ceremony, saying it was undermining readiness.

"Smooth and timely transitions of confirmed leadership are central to the defense of the United States," Austin said, adding he expected the Senate to "meet its responsibilities."

Pentagon spokesperson Sabrina Singh said last time the Marine Corps had an acting Commandant was from December 1, 1910 to February 2, 1911.

"The longer these unprecedented holds remain, the greater risk the Department runs in experiencing knowledge and expertise gaps in certain critical and often difficult to fill positions," Singh said.

After the U.S. Supreme Court last year overturned the landmark 1973 Roe v. Wade ruling recognizing a constitutional right to abortion, the Pentagon said it would cover travel costs for service members seeking abortions and up to 21 days off.

Several states have limited abortion access since Roe v. Wade was overturned, and the military argues that women service members cannot choose where they are stationed.

The Senate's approval of military promotions is usually smooth. Tuberville's hold cannot prevent the Democratic-majority Senate from voting on any promotion, but it can drastically slow down the process.

More high-profile posts are expected to be vacated in the coming months, including the top general leading the Army, the top admiral leading the Navy and the next chairman of the Joint Chiefs of Staff.

The nominee to become chairman, Air Force General Charles "C.Q." Brown, will field questions at his confirmation hearing on Tuesday before the Senate Armed Services Committee.

Berger's retirement leaves General Eric Smith, the Marine Corps' No. 2, also filling the role of "acting" commandant. He is President Joe Biden's nominee to become the next commandant but is expected to avoid major decisions without Senate confirmation.

(Reporting by Phil Stewart; additional reporting by Patricia Zengerle; Editing by Stephen Coates)