The single 400,000-pound H-4 Hercules flying boat, built by the Hughes Aircraft Co., was the largest flying boat ever built with the widest wingspan.

It was built after a U.S. government request in 1942 for a cargo and troop carrier that would not be susceptible to Axis submarines and not use critical wartime materials by substituting wood for metal in its construction.

The press nicknamed it the "Spruce Goose," a name Hughes hated because it insulted its builders and, in fact, the plane was built almost entirely of laminated birch, not spruce.

The cargo-type flying boat was designed to carry 750 fully-equipped troops or two Sherman tanks over long distances. It has a single hull, eight radial engines, a single vertical tail, fixed wingtip floats, and full cantilever wing and tail surfaces. The entire airframe and surface structures are composed of laminated wood and all primary control surfaces, except the flaps, are fabric covered.

The aircraft's hull includes a flight deck for the operating crew and a large cargo hold. A circular stairway connects the two compartments. Fuel bays, divided by watertight bulkheads, are below the cargo hold.

By 1947, the U.S. government had spent $22 million on the H-4 and Hughes had spent $18 million of his own money. Finally, on Nov. 2, 1947, Howard Hughes and a small engineering crew fired up the eight radial engines for taxi tests. Hughes lifted the giant aircraft 33 feet off the surface of Long Beach (Calif.) Harbor and flew it for one mile, for less than a minute, remaining airborne 70 feet off the water at a speed of 80 mph before landing. The H-4 Hercules never flew again.

Until he died in 1976, Hughes made sure the HK-1/H-4 was constantly maintained and kept in flight-ready condition.