US Army Secretary Dan Driscoll resigned after serving for about 18 months, the White House confirmed Monday. His departure comes amid months of reported tension with Defense Secretary Pete Hegseth, although the specific causes of their dispute have not been fully disclosed. Reuters also reported that Driscoll submitted his resignation amid the continuing strain.

The White House praised Driscoll in a statement to CBS, saying he had been highly effective in advancing President Donald Trump’s “Make America Strong Again” agenda and had shown exceptional leadership in military operations. It also cited his role in talks aimed at ending the Russia-Ukraine war. At 41, Driscoll was known as the youngest Army secretary in US history and was often called Trump’s “drone man.”

His resignation follows wider leadership changes at the Pentagon. Navy Secretary John Phelan left in April, while Army Chief of Staff General Randy George, General Christopher Donahue and other senior officers have recently departed. Reports linked Driscoll’s tensions with Pentagon leaders to George’s departure and disagreements over scaling back modernization and unmanned-technology initiatives.