The Spruce Goose – the Hughes H-4 Hercules, the Hughes Flying Boat – is the most famous military aircraft never used.

Conceived during World War II by dashing entrepreneur Howard Hughes, it was the world’s largest military transport plane – six times larger than any other aircraft at the time.

The war ended before the prototype, built of wood because of government restrictions on metals, had been completed. So Congress tried to kill the $25 million plane, by then mockingly known as the “Spruce Goose.” This led Hughes to go to Washington to fight for it.

“I put the sweat of my life into this project, and if it’s a failure, I’ll leave the country and never come back,” he said.

The plane finally took to the skies, with Hughes at the helm, in southern California on Nov. 2, 1947, but it barely made it aloft, getting just 70 feet into the air and staying airborne for all of one mile.

The flight garnered praise nonetheless.

“Hughes in Surprise Takeoff Proves Huge Plane’s Worth,” the Oregon Journal headlined.

The spectators assembled along the Long Beach waterfront to watch the spectacle included movie stars Cary Grant and James Stewart. An engineer and aviator, Hughes had branched out into movie producing.

“I think the airplane’s going to be fairly successful,” Hughes told reporters after stepping off the Spruce Goose.

The mammoth aircraft never flew again. Hughes, who became a recluse in his later years, died in 1976 at 70.

For the past three decades, the famous prototype – the sole Spruce Goose built – has been on display at the Evergreen Aviation & Space Museum in McMinnville.

The museum is marking the 75th anniversary of the plane’s flight with a celebratory event Wednesday and says it “is embarking on a yearlong campaign that honors the aircraft … cementing the aviation icon’s place in history.”