Sean Parnell, the Pentagon’s chief spokesperson, wrote on X that Phelan is leaving the administration and that the resignation is effective immediately.
Parnell, speaking on behalf of the secretary and deputy secretary of defense, thanked Phelan for his service to the department and the Navy and wished him well. He did not give a reason for the resignation.
Navy Undersecretary Hung Cao will serve as acting secretary. Cao is a retired service member who spent more than 20 years in the Navy, including deployments to combat zones.
The Navy secretary is the civilian head responsible for the training, equipping and administration of the Navy and Marine Corps. The post is filled through a presidential nomination and Senate confirmation and reports directly to the defense secretary.
Phelan is not a military commander, but he is a key member of the Pentagon’s leadership. His departure drew attention because it comes while the war is underway and as the Navy he led is spearheading a maritime blockade of Iran under orders from President Donald Trump.
The Associated Press called the resignation sudden, saying it came a day after Phelan delivered a speech at the Navy’s annual conference.
Some observers have suggested the move could be part of a broader leadership shake-up at the Pentagon, coming about 20 days after Defense Secretary Pete Hegseth fired Army Chief of Staff Randy George on April 2.
There has also been speculation that Phelan had clashed with Hegseth. The Wall Street Journal reported that last fall Phelan bypassed Hegseth to propose a modern warship concept directly to President Trump, which the defense secretary reportedly disliked.
* This article has been translated by AI.
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