The move is the latest major shakeup at the Pentagon under President Donald Trump's administration, which has already fired a series of senior officers this year.

The memo also calls for an additional 10 percent reduction in the number of general and flag officers, and a 20 percent cut in the number of general officers in the National Guard.

It did not specify how the reductions would be accomplished.

There were 38 four-star officers -- the highest rank that can usually be achieved in the US military -- and a total of 817 generals and admirals in the active-duty forces as of March 2025.

The cuts are aimed at removing "redundant force structure to optimize and streamline leadership by reducing excess general and flag officer positions," the memo said.

Hegseth later posted a video on X about the changes, which he dubbed "less generals, more GIs." In it, he said that despite the overall size of the military being far larger during World War II, there were fewer top officers at the time.

Hegseth said the cuts would be carried out in two phases, starting with those to four-star officers and National Guard generals, and followed by the 10 percent cuts to the overall number of generals and admirals.

- 'Where fat can be cut' -

"This is not a slash and burn exercise meant to punish high ranking officers," he said, adding: "This has been a deliberative process by working with the Joint Chiefs of Staff with one goal, maximizing strategic readiness and operational effectiveness," he said.

During his confirmation hearing in January, Hegseth argued that the Pentagon's bureaucracy was top-heavy and in need of cuts, telling lawmakers: "It's going to be my job, working with those that we hire and those inside the administration, to identify those places where fat can be cut, so it can go toward lethality."

Since beginning his second term in January, Trump has overseen a purge of top officers, including chairman of the Joint Chiefs of Staff general Charles "CQ" Brown, whom he fired without explanation in February.

Other senior officers dismissed this year include the heads of the Navy and Coast Guard, the general who headed the National Security Agency, the vice chief of staff of the Air Force, a Navy admiral assigned to NATO, and three top military lawyers.

Hegseth has insisted the president is simply choosing the leaders he wants, but Democratic lawmakers have raised concerns about the potential politicization of the traditionally neutral US military.

The Pentagon also announced in February that it aimed to reduce the number of its civilian employees by at least five percent, as Trump's administration moved to slash the federal workforce in the name of cost-savings.