Originally Published: 04 AUG 23 12:39 ET

Updated: 04 AUG 23 14:07 ET

By Natasha Bertrand and Oren Liebermann, CNN

(CNN) — Secretary of Defense Lloyd Austin has issued guidance to the military workforce for the first time about how Pentagon leadership roles will likely need to be reshuffled as a result of Republican Sen. Tommy Tuberville’s hold on military confirmations.

In a memo dated August 2 and obtained by CNN, Austin wrote that the “unprecedented, across-the-board hold is having a cascading effect, increasingly hindering the normal operations of this Department and undermining both our military readiness and our national security.”

As a result, Austin recommended a series of steps to try to mitigate the impact of the blockade that includes, “in extraordinary cases,” assigning lower-level officers in a grade of 0-8 or below to lead organizations in an acting capacity, Austin wrote. Commission officers are ranked from 0-1 to 0-10, with 10 being the four-star general or admiral level.

The memo comes as chief of staff of the Army, Gen. James McConville, retired without an official replacement on Friday, marking the second branch of the military without a confirmed leader. The last official commandant of the Marine Corps retired late last month.

The last time there was an acting chief of staff of the Army was in 2003 for two months, a Defense official told CNN. The Defense official added that the Missile Defense Agency, the entity responsible for developing the US’ layered defense against ballistic missiles, currently has a 1-star serving in an acting capacity for a 3-star general who has been nominated for the post. The agency is without a Senate-confirmed director for the first time since it was established in 2002, the official said.

Austin and Tuberville have spoken directly about the block at least twice, but no progress has been made yet in reaching a solution. Tuberville issued a blanket hold on the confirmations in protest of the Pentagon’s reproductive health policies.

Austin also wrote that because of the hold, three- and four-star officers will not be allowed to leave their current positions as they wait for confirmation for their next assignment. But they can stay in their current spot while performing the duties of another senior officer position if they are in the line of succession for that job.

Incumbent heads of organizations, moreover, “may be asked to remain in place until their successor has been nominated, confirmed, and appointed.” And officers currently in a deputy or vice position may assume the head role in an acting or temporary capacity, he added.

“I understand that these steps will not end or offset the risk to our readiness or our global leadership position,” Austin wrote. “Nor will they resolve the uncertainty and stress inflicted upon our general and flag officers and their families, or alleviate the worries rippling further down our ranks.”

In a sign of the growing challenges the military faces because of the ongoing holds, the Acting Commandant of the Marine Corps penned a letter to the force setting out his vision and expectations for the service in lieu of official guidance.

Gen. Eric Smith wrote the “intentionally broad” letter as guidance for the Marine Corps, highlighting the importance of discipline and cohesiveness in preparing for the next fight.

“This guidance maintains our momentum and confirms the direction of the Corps. It is intended to leave space for a future Commandant’s Planning Guidance,” Smith wrote. An incoming Commandant would typically issue official planning guidance for the Marines to outline the plan for the next service’s future. But as he awaits confirmation to lead the Marines, Smith wrote a letter instead.

Smith was nominated to serve as the next Commandant after Gen. David Berger retired last month, but he is carrying out the role in an acting capacity as his confirmation remains on hold.

“Until the Senate confirms our 39th Commandant, this guidance will serve as our reference point,” Smith wrote in the 4-page letter issued Thursday. “I cannot predict how long this process may take, but waiting is not an option for Marines, so we will move out as a team - just as we would in combat.”

Tuberville’s hold on military nomination now affect 301 senior officers, according to the Pentagon, including two members of the Joint Chiefs of Staff: the Commandant of the Marine Corps and, as of Friday, the Chief of Staff of the Army. That number will increase again later this month when the Chief of Naval Operations, Adm. Michael Gilday, retires.

This story has been updated with additional developments.