Final answer:
The President is ultimately responsible for the safety of all U.S. military and civilian personnel and property, working with the service branch secretaries, as part of their duty as Commander in Chief.
Step-by-step explanation:
The individual ultimately responsible for the safety of all military and civilian personnel and property, in conjunction with the respective service branch secretaries, is the President. This responsibility aligns with the President's role as Commander in Chief of the Army, Navy, Air Force, and Marine Corps as specified in Section 2 of the U.S. Constitution. The President, supported by the National Security Council and advised by the Secretary of Defense and the Joint Chiefs of Staff, also has the authority to require written opinions from these principal officers on any subjects relating to their duties, and oversees the U.S. armed forces including operational safety.