The Hughes H-4 Hercules (also known as the "Spruce Goose"; registration NX37602) is a prototype heavy transport aircraft designed and built by the Hughes Aircraft company. The aircraft made its first and only flight on November 2, 1947 and the project never advanced beyond the single example produced. Built from wood because of wartime restrictions on the use of aluminum and concerns about weight, its critics nicknamed it the "Spruce Goose" despite it being made almost entirely of birch rather than spruce. The Hercules is the largest flying boat ever built and has the largest wingspan of any aircraft in history. It survives in good condition at the Evergreen Aviation Museum in McMinnville, Oregon, USA.

In 1942, the U.S. War Department was faced with the need to transport war materiel and personnel to Britain. Allied shipping in the Atlantic Ocean was suffering heavy losses to German U-boats, so a requirement was issued for an aircraft that could cross the Atlantic with a large payload. Due to wartime priorities, the design was further constrained in that the aircraft could not be made of metal.