Which date marks the establishment of the U.S. Air Force?

The correct date marking the establishment of the U.S. Air Force is September 18, 1947. On this date, the Air Force was officially organized as a separate branch of the U.S. Armed Forces, following the National Security Act of 1947, which reorganized the military establishment and established the Department of the Air Force. This separation allowed for the distinct development of air power doctrine and operations, separate from the Army and Navy, recognizing the vital role of air combat and support.

In context, December 7, 1941, is significant as the date of the Pearl Harbor attack, which led the U.S. to formally enter World War II, but it does not pertain to the establishment of the Air Force. August 4, 1790, marks the establishment of the U.S. Coast Guard, while November 10, 1775, commemorates the founding of the U.S. Marine Corps. Each of these dates is important in U.S. military history, but they relate to different branches and events rather than the establishment of the Air Force.