Douglas Aircraft Company was an early American aerospace and defense company that was based in Southern California. The company was founded in 1921 by Donald Wills Douglas Sr. In its early days, one of its aircraft was the first to circumnavigate the world by air. The company became well-established during World War II, building several aircraft, including the C-47 Skytrain, the A-26 Invader, and collaborating with Boeing on the B-17 Flying Fortress.