Washington. Navy Secretary John Phelan is leaving his job, the Pentagon abruptly announced Wednesday, the first head of a military service to depart during President Donald Trump’s second term but just the latest top defense leader to step down or be ousted.

No reason was given for the unexpected departure of the Navy’s top civilian official, coming as the sea service has imposed a blockade of Iranian ports and is targeting ships linked to Tehran around the world during a tenuous ceasefire in the war.

Phelan’s departure is the latest in a series of shakeups of top leadership at the Pentagon, just weeks after Defense Secretary Pete Hegseth fired the Army’s top uniformed officer, Gen. Randy George. Hegseth has also fired several other top generals, admirals, and other defense leaders since taking office last year.

Showing how sudden the latest move was, Phelan the day before had addressed a large crowd of sailors and industry professionals at the Navy’s annual conference in Washington and spoke with reporters about his agenda.

Pentagon spokesman Sean Parnell said in a social media post that Phelan was “departing the administration, effective immediately," and Undersecretary Hung Cao will become acting secretary.

Cao ran a failed US Senate bid in Virginia in 2024 to unseat Democratic Senator Tim Kaine. He had Trump’s endorsement in the crowded Republican primary.

Cao is a 25-year Navy veteran who served in combat zones. His biography includes fleeing Vietnam with his family as a child in the 1970s. In a campaign video for his Senate bid, he compared Vietnam’s communist regime during the Cold War to the administration of President Joe Biden.

“We are losing our country,” Cao said in a video during the campaign, which blamed Biden for the criminal cases against Trump and showed footage of border crossings and store lootings. “You know it. But you also know that you can’t say it. We’re forced to say that wrong is right. We’re forced to lie.”

Phelan had not served in the military or had a civilian leadership role in the service before President Donald Trump nominated him for secretary in late 2024.

Phelan was a major donor to Trump’s campaign and founded the private investment firm Rugger Management LLC. According to his biography, Phelan’s primary exposure to the military came from an advisory position he held on the Spirit of America, a non-profit that supported the defense of Ukraine and the defense of Taiwan.