"The Spirit of St. Louis" -- a custom-built, single engine, single-seat monoplane that Charles Lindbergh flew on the first solo non-stop flight across the Atlantic Ocean on May 20-21, 1927. On display at the Smithsonian Air and Space Museum in Washington, D.C.

In 1925, Ryan Airlines was founded by Benjamin Franklin Mahoney and T. Claude Ryan. Mahoney bought out Ryan's shares in 1926, but Ryan stayed involved with the firm.

In 1927, a number of pilots were competing to develop aircraft that would be capable of flying from New York to Paris. Lindbergh, an air mail pilot, contacted Ryan Airlines to see if they could deliver a plane. He liked the company's Ryan M-2 mailplane, which first saw service in 1926. The company said it could deliver a custom-built aircraft within three months.

The plane was designed by Donald A. Hall, with input from Lindbergh. The name came from Lindbergh's home town of St. Louis, Missouri.

Lindbergh pushed for a single engine in the belief that this reduced the change of engine failure. He also believed that the lighter weight would increase fuel efficiency. The wingspan of the Ryan M2 was increased by 10 feet and redesigned slightly to Lindbergh's specifications to provide greater lift. (The finished aircraft had a range of 4,000 miles.) The Spirit of St. Louis one of the most streamlined aircraft yet built, and had a lightweight fabric skin. The fuselage was lightweight metal tubing, but the wings were a wooden frame.

Lindbergh chose the Wright J-5C "Whirlwind" radial engine for the plane. The 223 horsepower engine was very reliable, and air-cooled. It was also self-lubricating, at a time when most engine pistons had to be lubricated every few hours. The engine was built at 24-year old Tom Rutledge.

The 450 gallon fuel tank was placed in front of the cockpit, rather than behind it. This meant Lindberg would probably not survive a crash, but improved the plane's center of gravity. This also meant that there was no front window. Lindbergh had to navigate by looking out the side windows, or by using a periscope. (It is not clear that the periscope was ever used.)

A special compass, which automatically corrected for his flight across the Atlantic (and the changing position of the North Pole relative to his plane), was used for guidance.