Secretary of the Navy John Phelan is departing the Trump administration effective immediately, a Pentagon spokesperson announced Wednesday.

“On behalf of the Secretary of War and Deputy Secretary of War, we are grateful to Secretary Phelan for his service to the Department and the United States Navy,” Sean Parnell said in a post on X. “We wish him well in his future endeavors.”

Parnell said Undersecretary Hung Cao will become acting secretary of the Navy.

Phelan’s abrupt departure without an explanation follows the removal of a number of other top military officials since President Donald Trump returned to the White House last year.

This month, Defense Secretary Pete Hegseth ousted the Army’s chief of staff, Gen. Randy George, from his role without explanation. Two other top Army officials, Maj. Gen. William Green Jr. and Gen. David Hodne, were removed as well.

Hegseth has also fired Chairman of the Joint Chiefs of Staff Gen. Charles Q. Brown, Chief of Naval Operations Adm. Lisa Franchetti, Air Force Vice Chief of Staff Gen. James Slife and the head of the Defense Intelligence Agency, Lt. Gen. Jeffrey Kruse.

Phelan’s departure comes as the Navy is actively carrying out a blockade against Iran.

He had no prior military experience before he was confirmed as the Navy secretary last year. However, he was a financier who fundraised millions of dollars for Trump’s 2024 presidential campaign.

The announcement comes just a few days after the Navy League’s annual Sea Air Space conference, where Phelan delivered a keynote address and discussed his vision for the Navy, including a renewed focus on shipbuilding.

The timing and circumstances of Phelan’s separation were not immediately apparent. As the service’s top civilian official, Phelan on Tuesday took part in the Pentagon’s budget rollout — which includes $87 billion for shipbuilding — and explained the Navy’s priorities ahead of budget hearings on Capitol Hill.

Cao, who retired at the rank of captain and lost a challenge to Sen. Tim Kaine in 2024, graduated from the U.S. Naval Academy and has served in the military for more than 25 years, including deployments in Iraq, Afghanistan and Somalia.

He will take over Navy at a time when the administration is struggling with shipbuilders to overcome persistent delays and backlogs in maintenance and construction. Trump made plans to “resurrect” naval and commercial shipbuilding a signature pledge in his 2025 State of the Union speech.

In a sign that that’s been easier said than done, Office of Management and Budget Director Russell Vought this week ripped into shipbuilders over those problems, saying, “Backlogs are leading to a fleet-wide operational death spiral.” Vought also holds an important role as the supervisor of the administration’s shipbuilding office.