United States Department of the Army The Department of the Army ( DA ) is one of the three military departments within the Department of Defense of the United States of America . The Department of the Army is the Federal Government agency which the United States Army is organized within , and it is led by the Secretary of the Army who has statutory authority to conduct its affairs and to prescribe regulations for its government , subject to the limits of the law , and the directions of the Secretary of Defense and the President . The Secretary of the Army is a civilian official appointed by the President and confirmed by the Senate . The highest - ranking military officer in the department is the Chief of Staff of the Army , who is also a member of the Joint Chiefs of Staff . Other senior officials of the Department are the Under Secretary of the Army ( principal deputy to the Secretary ) and the Vice Chief of Staff of the Army ( principal deputy to the Chief of Staff . ) The " Department of War " was originally formed in 1789 as an Executive Department of the United States , and was renamed by the National Security Act of 1947 to the Department of the Army on September 18 , 1947 . By amendments to the National Security Act of 1947 in 1949 , the Department of the Army was transformed to its present - day status . Organizational structure . The Department of the Army is a Military Department within the United States Department of Defense . The Department is headed by the Secretary of the Army , who by statute must be a civilian , appointed by the President with the confirmation by the United States Senate . The Secretary of the Army is responsible for , and has the authority to conduct all the affairs of the Department of the Army , subject to the authority , direction and control of the Secretary of Defense . The Department of the Army is divided between its Headquarters at the Seat of Government and the field organizations of the Army . By direction of the Secretary of Defense , the Secretary of the Army assigns Army forces , apart from those units performing duties enumerated in ( i . e . organize , train & equip ) or unless otherwise directed , to the operational command of the Commanders of the Combatant Commands . Only the Secretary of Defense ( and the President ) has the authority to approve transfer of forces to and from Combatant Commands . . Headquarters , Department of the Army . " Headquarters , Department of the Army " is the corporate office of the Department which exercises directive and supervisory functions and consists of two separate staffs ; the " Office of the Secretary of the Army " ( ) , the mainly civilian staff ; and the " Army Staff " ( & ) , the mainly military staff . The Office of the Secretary and the Army Staff are organized along similar lines , with civilians and military officers both overseeing similar program areas . Office of the Secretary . The Office of the Secretary is led by the Secretary of the Army , assisted by the Under Secretary of the Army and the Administrative Assistant to the Secretary of the Army , who is the senior civilian career official of the Department . The Office of the Secretary of the Army , also known as the " Army Secretariat " , is divided into multiple branches with functional responsibilities , the six most important of which are headed by one of the five Assistant Secretaries of the Army or the General Counsel of the Army , each of whom are civilians appointed by the President and confirmed by the Senate . The Army Staff . The Army Staff is led by the Chief of Staff of the Army , a four - star general who is the highest - ranking officer in the Army and the Army member of the Joint Chiefs of Staff . The Chief of Staff is assisted in managing the Army Staff by the Vice Chief of Staff of the United States Army , a four - star general and second - highest - ranking officer in the Army . The Army Staff is divided into several directorates , each headed by a three - star general . A key official within the Army Staff is the Director of the Army Staff , who is a three - star general . The Director is responsible for integrating and synchronizing the work of the Office of the Secretary and the Army Staff so that they meet the goals and priorities of the Secretary of the Army . Other key figures within the Army Staff are the Sergeant Major of the Army , the United States Army Judge Advocate General , the Chief of the Army Reserve , the Chief of the National Guard Bureau , the United States Army Provost Marshal General , and the United States Army Surgeon General