Final answer:
The President of the United States is directly responsible for all command functions, as well as the safety and efficiency of the military, serving as Commander in Chief as specified in the Constitution.
Step-by-step explanation:
The individual directly responsible for all command function, and who bears absolute responsibility for the safety, well-being, and efficiency of the command is the President of the United States. As outlined in Section 2 of the Constitution, the President serves as the Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States when called into service. This role encompasses a broad range of duties, including but not limited to, requiring written opinions from principal officers of the executive departments on subjects related to their duties, and having the power to grant reprieves and pardons for offenses against the United States, with the exception of cases of impeachment.