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 and 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. Another Trump loyalist is taking over as acting head of the Navy: Undersecretary Hung Cao, a 25-year Navy combat veteran who ran unsuccessful campaigns for the U.S. Senate and House in Virginia.

Phelan's departure is the latest in a series of shakeups of top leadership at the Pentagon, coming 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 defense leaders since taking office last year.

The firings began in February 2025, when Hegseth removed military leaders including Adm. Lisa Franchetti, the Navy's top uniformed officer, and Gen. Jim Slife, the No. 2 leader at the Air Force. Trump also fired Gen. Charles "CQ" Brown Jr. as chairman of the Joint Chiefs of Staff.

Showing how sudden the latest move was, Phelan had addressed a large crowd of sailors and industry professionals on Tuesday at the Navy's annual conference in Washington and spoke with reporters about his agenda. He also hosted the leaders of the House Armed Services Committee to discuss the Navy's budget request and efforts to build more ships, according to a social media post from his office.

Pentagon spokesman Sean Parnell said in a post on X that Phelan was "departing the administration, effective immediately."

Phelan had not served in the military or had a civilian leadership role in the service before Trump nominated him for secretary in late 2024. He was seen as an outsider being brought in to shake up the Navy.

Phelan was a major donor to Trump's campaign and had 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 nonprofit that supported the defense of Ukraine and the defense of Taiwan.

In his role leading the Navy, Phelan had championed the "Golden Fleet," a major investment in new ships including a new "Trump-class" battleship. But Phelan's leadership was marred by feuds with senior leaders throughout the Pentagon, including Hegseth and Deputy Defense Secretary Stephen Feinberg, Pentagon and congressional officials said.

Tensions had been simmering for months between Phelan and his two bosses -- Hegseth and Feinberg -- over management style, personnel issues and other matters.