Who serves as the principal military advisor to the U.S. President and the National Security Council?

The correct choice is the Chairman of the Joint Chiefs of Staff, who serves as the principal military advisor to the President of the United States and the National Security Council. This position is critical as it involves providing strategic military advice, ensuring that the highest levels of government receive informed perspectives on defense and security matters. The Chairman is responsible for integrating and coordinating the views of the various branches of the military and is a key player in national defense strategy formulation and execution.

The other options, while important roles within the military structure, do not hold the same level of authority and responsibility in advising the President directly. The Vice Chairman of the Joint Chiefs of Staff assists the Chairman but does not serve as the principal advisor. The Director of Operations is focused on the operational aspects of military strategy rather than strategic military advice to the government. The Secretary of Defense oversees the Department of Defense and its operations, but it is the Chairman who specifically serves in the advisory capacity to the President and National Security Council.