"The Hughes Flying Boat represents one of man’s greatest attempts to conquer the skies as the largest airplane ever constructed. It flew only one time on November 2, 1947. Conceived as a personnel and materiel carrier, the single hull prototype was designed to fly Trans-Atlantic to avoid World War II German submarines that were sinking Allied ships in large numbers. Completed in 1947 after the end of the War, the wooden winged giant is nearly six times bigger than any aircraft of its time. The press insisted on calling the Hughes Flying Boat the “Spruce Goose,” a name that its billionaire builder Howard Hughes despised. Most of the huge plane is actually made of birch, with only small amounts of maple, poplar, balsa, and, yes, spruce. Birch was chosen because testing proved it light, strong, and resistant to splitting, dry rot and deterioration."
Text from http://www.sprucegoose.org/aircraft_artifacts/Aircraft/PostWarYears/HK-1.htm