The command of the army of the United States rests with the constitutional commander in-chief, the President, who places parts of the army and separate armies whenever constituted under commanders subordinate to the general command; and, in case of exigency seeming to him to require it, he may place the whole army under a single commander subordinate to him; but in time of peace and ordinary conditions the administration and control of the army are effected without any second in command. The President's command is exercised through the Secretary of War and the Chief of Staff. The Secretary of War is charged with carrying out the policies of the President in military affairs. He directly represents the President and is bound to act in conformity to the President's instructions. Under the law and the decisions of the Supreme Court his acts are the Presi dent's acts and his directions and orders are the President's directions and orders. The Chief of Staff reports to tae Secretary of War, acts as his military adviser, receives from him the directions and orders given in behalf of the President and gives effect thereto. For pur poses of administration the office of the Chief of Staff constitutes a supervising military bureau of the War Department.
The general staff of a command consists of general staff officers of such number and grades as may be assigned to it on the recommenda tion of the Chief of Staff. The senior general staff officer on duty with a command, unless otherwise directed by the War Department, is the chief of staff of the command. Ordinarily
he is so assigned by the War Department. The duties of the chief of staff of a command are as prescribed for officers of the General Staff Corps, and in addition he, under direction of the commander of the troops, performs all duties analogous to those devolved upon the Chief of Staff of the army. The other general staff officers serving with troops are employed under the direction of the commanders thereof upon the duties prescribed for officers of the General Staff Corps, and they perform such other duties within the scope of general staff employment as may be directed by such com manders. General staff officers are not as signed to other than general staff duties except by special authority of the War Department. The two general officers authorized for the General Staff Corps are detailed by the Presi dent from officers of the army at large and below the grade of brigadier-general. All vacancies that may occur in General Staff Corps in grades below that of brigadier-general are filled on the recommendation of a board of five general officers of the line, not more than two of whom shall be members of the General Staff Corps, convened by the War Department at such times as may be necessary. The board is sworn to recommend officers solely on their professional efficiency and on their probable aptitude and fitness for general staff service, and selects such number of officers of the proper grades to fill existing or expected vacan cies as the War Department may 'direct.