Due to wartime restrictions on the availablity of metals, the H-4 was built almost entirely of laminated birch (not spruce). The aircraft was a marvel in its time. It married a soon-to-be outdated technology (flying boats) to a massive airframe that required some truly ingenious engineering innovations.
In 1942, the US War Department was faced with the need to transport war material and personnel to Britain. Allied shipping in the Atlantic 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.
The aircraft was the brainchild of Henry Kaiser, who directed the Liberty ships program. He teamed with aircaft designer Howard Hughes to create what would become the largest aircraft ever built or even seriously contemplated at that time. When completed, it would be capable of carrying 750 fully-equipped troops or two Sherman tanks.
To conserve metal for the war effort, it would be built mostly of wood: hence the Spruce Goose moniker. It was also referred to as the Flying Lumberyard by critics who believed an aircraft of its size simply could not fly.
Development dragged on and was not completed until well after the war was over. In 1947, Howard Hughes was called to testify before Congress, which was eliminating war-era spending to free up Federal funds for domestic projects. Though he encountered skepticism and even hostility from the committee, Hughes remained unruffled. During a break in the hearings, he returned to California, ostensibly to run engine tests on the H-4. On November 2, 1947 with Howard Hughes personally at the controls, the Spruce Goose lifted off from the waters off Long Beach, remaining airborne 70 feet off the water at a speed of 80 miles per hour for just under a mile.
Hughes had proved the critics wrong, but the justification for continued spending on the project was gone. Congress killed the Spruce Goose project, and the aircraft never flew again. It was carefully maintained in flying condition until Hughes's death in 1976.
Though the project was always unlikely to produce a useful aircraft given the technological limitations of the era, the H-4 Hercules in some senses presaged the massive transport aircraft of the late 20th century, such as the Lockheed C-5 Galaxy and the Antonov An-124 and An-225. The Spruce Goose demonstrated that the physical and aerodynamic principles which make flight possible are not limited by the size of the aircraft.
Hughes HK-1 "Spruce
Approx. 3 000
6 370 m
and Whitney R-4360, 3 000 hp each size=2>Propellers
bladed Hamilton Standards, diameter 5,23 m (17'
Hughes HK-1 "Spruce Goose"