Milley -- the chairman of the Joint Chiefs of Staff -- urged the Senate to begin approving the nominations, which have been stalled for months due to a single conservative legislator's opposition to Defense Department policies aimed at easing abortion access for US troops.

The Pentagon insists the policies will stay, and the impasse has left an unprecedented three branches of the US military -- the Army, Navy and Marine Corps -- with leaders serving on an acting basis, while a number of other important positions are also unfilled.

"It's very plausible that an adversary could misread the United States and perceive that the United States was in a situation of internal division, instability, confusion, friction at the highest levels of its military," Milley said in an interview aboard a US military aircraft.

"You want your adversary not to misunderstand you," the general said. "They may think that somehow you're weaker, and it may embolden them to seize opportunities they might not otherwise have taken."

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

The Defense Department responded by permitting service members to take administrative absences to receive "non-covered reproductive health care," and establishing travel allowances to help them cover costs.

But Senator Tommy Tuberville, a Republican from Alabama, insists those efforts are illegal and has vowed to delay the approval of senior officers as well Defense Department civilian officials until they are reversed.

- 'Ultimate form of legitimacy' -

He is preventing more than 300 nominees from being quickly approved by the Senate via unanimous consent, and while lawmakers can still vote on nominations individually, that much more time-consuming process has not been used so far.

Milley said far more than 300 people are ultimately affected by the situation.

"Somewhere probably in the range of 20 to 30 percent of all the organizations in the military are being somehow impacted with a lack of predictability and certainty of leadership rotations," which "creates a certain degree of instability in leadership, and uncertainty in leadership," he said.

Additionally, there are spouses who "don't have predictability, so they can't plan for jobs if they transfer to a new station," while "some of the kids can't start new schools during the normal rotation in the summer, so there's a human dimension to all of this."

At the very top of the US armed forces, there are currently three officers who are serving as the acting heads of military branches and on the Joint Chiefs of Staff while also performing their previous jobs as deputy service chiefs.

If General Charles Brown -- who has been nominated to replace Milley when he leaves office next month -- is not confirmed by the Senate in time, half of the eight members of the Joint Chiefs of Staff will soon hold acting positions.

"Our fundamental task is to support and defend and protect the constitution of the American people. We're going to continue to do that no matter what rank we are, whether we're confirmed or not," Milley said.

However, "Senate confirmation is the ultimate form of legitimacy conferred by the American people through their elected representatives," he said.

"When you don't have a Senate confirmation, you're getting an officer who's in an acting role, and is not fully empowered by the people of the United States."