Dan Driscoll has resigned as US Army secretary after serving in one of the top civilian roles in the Army. The White House said on Monday that Driscoll sent his resignation to President Donald Trump. His exit adds to a long list of senior changes at the US Defense Department. It also comes as the Pentagon faces new debate over military leadership, Army plans, and the future of US defense policy. Driscoll was second in line to Defense Secretary Pete Hegseth. Reports had said he was considering leaving the Pentagon after friction with Hegseth. The White House did not give a reason for his resignation. White House officials praised Driscoll for his work. They said he helped carry out Trump's defense plans and placed a strong focus on Army readiness and combat power. They also credited him with helping talks linked to the Russia and Ukraine war. His work also covered new military tools and faster ways to build them. Driscoll took office after the Senate confirmed him in February 2025. Senators voted 66 to 28 to approve his nomination. His hearing focused on Army reform, better recruiting, new weapons, and a stronger defense industry. Before joining the Army leadership, Driscoll had a varied career. He served as an Iraq war veteran and later worked as a tech investor. He also advised JD Vance. Driscoll met Vance while both were at Yale Law School. Trump later chose Driscoll for the Army post and called him a person who could bring change to the service. During his time as Army secretary, Driscoll became known for his focus on modern war. He pushed for faster work on drones and tools that can stop enemy drones. Drones have changed the way many modern wars are fought. They can watch large areas, find targets, and strike from far away. Counter drone tools can help protect troops and key sites. Driscoll also sought to cut delays in defense work. His goal was to help military firms build and test new tools faster. He saw speed as a key need for the Army. His work also reached beyond normal Army duties. Driscoll was given a key role in talks tied to the war between Russia and Ukraine. The task gave him a rare role in a major foreign policy effort. His resignation follows other major changes in Army leadership. Army Chief of Staff Randy George left his post in April. Driscoll had been an ally of George and spoke with support for him after his departure. In April, Driscoll told Congress that he and his family went to George's home after George left office. He said they met him and gave him a hug. Driscoll also said civilian leaders have the right to choose the military leaders they want. That view reflects the role of civilian control in the US defense system. In June, General Christopher Donahue also left his role as head of US Army forces in Europe and Africa. His departure came as the Pentagon continued to see changes among senior officials. The Defense Department has also dealt with leak probes, budget concerns, and other internal issues in recent months. The changes have raised fresh attention on how the department is managed. Driscoll's exit now creates another change at the top of the Army. The next Army secretary will face a wide set of tasks. Those tasks include improving readiness, building new weapons, growing drone defenses, helping recruitment, and supporting the defense industry. The new leader will also work under a Pentagon leadership team that is still shaping its plans for the US military. For now, Driscoll's resignation marks the end of his time as Army secretary. His record includes work on Army reform, new technology, military readiness, and talks tied to the Russia and Ukraine war. The leadership change may also shape the Army's next steps on technology, recruitment, and defense planning. More details about the next Army secretary are expected as the administration moves forward.