Final answer:
The claim that the Secretary of Defense was a cabinet-level position before 1947 is false. The Department of Defense, along with the cabinet position of Secretary of Defense, was officially established in 1949 after the reorganization of the military branches under the National Security Act of 1947.
Step-by-step explanation:
The statement that until 1947 one of the president's cabinet-level positions was the Secretary of Defense, who headed the Defense Department, is false. In fact, the Department of Defense was officially created in 1949. Prior to this, there was the Department of War, established in 1789, which along with the Department of the Navy (1798), the Department of the Army (1947), and the Department of the Air Force (1947), were all reorganized under the Department of Defense in 1949. The reorganization was a part of the National Security Act of 1947, which aimed to streamline the U.S. military and security apparatus in the wake of World War II and the beginning of the Cold War.