John Barron McKay (December 8, 1922 – April 27, 1975) was an American naval officer, World War II pilot, aeronautical engineer, and test pilot. He was one of twelve pilots who flew the North American X-15, an experimental spaceplane jointly operated by the United States Air Force and NASA. On September 28, 1965, he flew the X-15 to an altitude above 50 miles, thereby qualifying as an astronaut according to the United States definition of the boundary of space. However, this altitude did not surpass the Kármán line, the internationally accepted boundary of 100 kilometers (62 miles).