What established the function of each branch of the Armed Forces?

The correct answer is that the Key West Agreement of 1948 established the function of each branch of the Armed Forces. This agreement was significant as it delineated the roles and responsibilities of the Army, Navy, Air Force, and Marine Corps, which was essential for maintaining clarity and cooperation among the different branches during the Cold War.

By defining how each service would interact and operate, the Key West Agreement facilitated a more integrated approach to defense, ensuring that each branch could do its part while preventing overlap and confusion regarding command and control. This foundational framework contributed to the organized structure that the U.S. military relies on to this day.

While the National Security Act of 1947 and the Goldwater-Nichols Act are pivotal pieces of legislation in the history of U.S. military organization, they focused more on the overall structure of defense and inter-service cooperation rather than explicitly defining the individual functions of each branch. The Defense Reorganization Act also played a role in reorganizing the military, but it did not set the functional boundaries for each branch as the Key West Agreement did.