More than 300 nominations -- including the generals selected as the next heads of the Army and the Marine Corps -- are awaiting confirmation by the US Senate, and the number continues to grow.

The Senate can still vote on nominees individually, but the "hold" by Senator Tommy Tuberville, a Republican from Alabama, means they cannot be quickly approved in groups by unanimous consent.

"Unfortunately, today, for the first time in the history of the Department of Defense, two of our services will be operating without Senate-confirmed leadership," Defense Secretary Lloyd Austin said at a ceremony marking the end of General James McConville's tenure as chief of staff.

"The failure to confirm our superbly qualified senior uniformed leaders undermines our military readiness. It undermines our retention of some of our very best officers. And it is upending the lives of far too many of their spouses, children, and loved ones," he said.

The Pentagon has emphasized that the delay in approving the nominations is negatively impacting military families, as they are unable to plan for things such as school for their children given the uncertainty about where they will be living.

- Lives, careers 'in limbo' -

General Randy George -- the current vice chief of staff of the Army -- has been nominated to replace McConville as the head of the service and will perform those duties in an acting capacity in addition to his current job.

"We need the Senate to act not only on his nomination but also on the over 300 other general and flag officers across the armed services whose careers and lives are now in limbo because of this unprecedented hold," Secretary of the Army Christine Wormuth said at the ceremony.

The US Supreme Court in June 2022 struck down the nationwide right to abortion, meaning troops stationed in places that restricted or banned the procedure must now take leave and travel to areas where it is legal to obtain one.

In response, Austin directed the Defense Department to develop policies -- which were released in February -- to allow service members to take administrative absences to receive "non-covered reproductive health care," and to establish travel allowances to help them cover costs.

Tuberville insists those efforts are illegal and has vowed to delay the approval of senior officers as well Defense Department civilian officials until it is reversed.

The US Marine Corps commandant stepped down on July 10, and the general nominated to replace him has been performing two jobs -- vice commandant and head of the service -- for nearly a month.

The problem is set to worsen as other top officers are leaving office soon, including Chief of Naval Operations Admiral Mike Gilday and Chairman of the Joint Chiefs of Staff General Mark Milley.