Who is the principal military advisor to the secretary of defence?

The principal military advisor to the Secretary of Defense is the Chairman of the Joint Chiefs of Staff (CJCS). This position is held by a senior officer from one of the U.S. Armed Forces branches, and the CJCS provides strategic advice, oversees military operations, and helps coordinate the activities of the Joint Chiefs of Staff. Additionally, the CJCS plays a key role in advising the President and the National Security Council on military matters.