Final answer:
The decision to use non-DOD property for live fire exercises must be approved by the President of the United States, who is the Commander in Chief of the armed forces according to the Constitution.
Step-by-step explanation:
The decision to use non-Department of Defense (DOD) property for live fire exercises is a significant one and typically involves many levels of authorization due to the nature of military operations and the potential use of civilian land. According to the Constitution and military structure, the President of the United States, as the Commander in Chief of the armed forces, has the ultimate authority over military affairs. This includes decisions on the use of non-DOD property for exercises such as live fire training.
Therefore, the correct answer to the question is that the decision must be approved by the President of the United States. While the Secretary of Defense oversees the entire Department of Defense as a civilian head and the Joint Chiefs of Staff are top military advisors to the President, a decision of such nature falls under the purview of the President. Additionally, it is the President who may send troops into hostile situations but must seek congressional approval for extended military actions beyond 60 days, highlighting the President's key role in military operations decisions.