US Army Secretary Dan Driscoll has submitted his resignation after about 18 months in the role.
His departure was confirmed by CBS, the BBC's US media partner, which reported it followed months of conflict between him and Defence Secretary Pete Hegseth.
The youngest-ever army secretary has often been called President Donald Trump’s “drone guy.”
Driscoll, 41, was praised by the White House for his effectiveness in advancing Trump’s “Make America Strong Again” agenda and for outstanding leadership during military operations.
The BBC sought comment from the White House, Pentagon and Army.
He is not the only senior leader to leave recently; Navy Secretary John Phelan resigned abruptly in April, and Army chiefs such as Randy George, David Hodne and William Green have also departed.
Since Hegseth became Defence Secretary, more than a dozen senior military officers, including the chief of naval operations and the Air Force’s vice‑chief of staff, have been fired.
Details of the friction between Driscoll and Hegseth remain unclear, but reports indicate Driscoll is close friends with Randy George, who was asked by Hegseth to resign.
The army secretary position is the top civilian role in the US Army, overseeing active duty troops, National Guard and reserve soldiers.
Driscoll’s earlier service included leading a cavalry platoon and deploying to Iraq in 2009.
He earned the nickname “drone guy” for his embrace of emerging battlefield technologies and played a key role in talks to end the Russia‑Ukraine war, meeting Ukrainian President Volodymyr Zelensky and traveling abroad.
He also maintains close ties with Vice‑President JD Vance, whom he met at Yale Law School.
During his tenure he oversaw the deployment of National Guard units to US cities and served as acting director of the Bureau of Alcohol, Tobacco, Firearms and Explosives.
