Which branch of the US Military did not officially form until 1947?

The formation of the U.S. Air Force as an independent branch of the military in 1947 is significant because prior to this, air operations were managed under the Army's jurisdiction. The National Security Act of 1947 established the Air Force as a separate branch to better organize and manage air power as the importance of aerial capabilities became increasingly recognized after World War II. This decision was influenced by the strategic necessity for a dedicated military structure that could focus on the growing role of air power in national defense. The Navy, Army, and Coast Guard were all established before this period, with histories going back to the late 18th century or early 19th century. Hence, the U.S. Air Force is the branch that officially formed in 1947, making it unique in terms of its establishment timeline among the primary branches of the U.S. military.