Hughes H-4 Hercules (Spruce Goose): Howard Hughes’s giant flying boat

Its wingspan is wider than a football field is long, it is made almost entirely of wood and it flew exactly once for about half a minute: the Hughes H-4 Hercules, known worldwide as the “Spruce Goose,” is one of the quirkiest and at the same time most fascinating chapters of aviation history. It began as a wartime project, didn’t take off until after the war ended and then vanished into a hangar for decades. This article tells how Howard Hughes’s giant flying boat came to be, what sets it apart technically, how the famous flight in Long Beach harbor went and where you can see the Spruce Goose up close today.

The Spruce Goose in brief

The H-4 Hercules is an eight-engine transport flying boat that Howard Hughes had built in California in the 1940s. It was meant to carry soldiers and materiel across the Atlantic without relying on ships. Exactly one was built, registered as NX37602. It flew just once, on November 2, 1947, and today stands in a museum in Oregon. With its wingspan of around 97.5 meters, it is still the largest flying boat ever built.

How the H-4 came about

In 1942, German U-boats were sinking cargo ship after cargo ship in the Atlantic. The Allies were looking for ways to get supplies to Europe without the endangered convoys. The industrialist Henry J. Kaiser, known for his Liberty ships built in record time, pushed a radical idea: giant flying boats that fly troops and cargo across the ocean.

Kaiser, however, lacked experience in aircraft construction. So he teamed up with Howard Hughes, who already had a name through his company Hughes Aircraft and as a record-setting pilot. According to the museum where the aircraft stands today, the two signed a contract for the design at the Beverly Hills Hotel on November 16, 1942. The project initially ran under the designation HK-1 – for Hughes and Kaiser – and called for three aircraft within two years.

Kaiser’s exit and the new name

The schedule was barely achievable from the start. Hughes was considered a perfectionist who wanted to check every detail himself, and wooden construction on this scale was uncharted territory. Kaiser eventually withdrew. Hughes continued the project alone, under a new contract that called for only a single aircraft. From 1944 it was called the H-4 Hercules. Development costs ultimately added up to around 23 million US dollars – an enormous sum for the time.

The H-4 was built in Culver City at the Hughes airfield, on a site in what is now the Playa Vista neighborhood of Los Angeles. That is only a few kilometers north of today’s Los Angeles Airport. Anyone on a spotting trip to Los Angeles today is therefore very close to the workshops where the giant flying boat was built.

Technology: a giant made of wood

The most striking feature of the H-4 is its building material. Aluminum was rationed during the war and reserved for combat aircraft. The requirement was therefore to build the flying boat from “non-strategic” materials. Hughes relied on the Duramold process: thin wood veneers are glued with synthetic resin and pressed under heat and pressure into a very strong plywood. The veneer was predominantly birch. According to the museum, almost all parts are made of wood, apart from the engines, electrics, screws and some reinforcements added during restoration. The elevators and rudder were fabric-covered.

The H-4 is built as a high-wing flying boat with a seaworthy boat hull. Floats hang under the outer thirds of the wings and stabilize the flying boat on the water. On the leading edge of the wing sit eight engine nacelles with large four-blade propellers.

Feature	Hughes H-4 Hercules
First flight	November 2, 1947 (only flight)
Wingspan	319 ft 11 in (around 97.5 m)
Length	218 ft 8 in (around 66.7 m)
Height	79 ft 4 in (around 24.2 m)
Powerplant	8 × Pratt & Whitney R-4360 Wasp Major
Propellers	Hamilton Standard, four-blade, a good 5.2 m in diameter
Construction	Duramold plywood, predominantly birch
Registration	NX37602
Built	1

Eight Wasp Majors on the wing

For power, Hughes chose eight Pratt & Whitney R-4360 Wasp Major engines, air-cooled radial engines with 28 cylinders in four rows and around 3,000 hp each. The engine was one of the most powerful piston engines of its time and later also powered types such as the Boeing 377 Stratocruiser. Measured by wingspan, the H-4 is still the largest propeller aircraft ever built.

What it was meant for

The H-4 was designed as a troop and cargo transport. According to the planning data, it was supposed to carry around 68 tonnes of payload – for example a large number of fully equipped soldiers or two M4 Sherman battle tanks. Figures for the number of soldiers differ: the museum cites up to 400, other accounts up to 750. Performance figures such as cruising speed and range remained theoretical anyway, because the H-4 never flew in service.

Howard Hughes: aviator, film producer, entrepreneur

Without the person Howard Hughes, the H-4 is hard to understand. Born in Houston in 1905, the heir to a tool company produced films in Hollywood such as the aviation drama “Hell’s Angels” and was at the same time an ambitious pilot. In 1932 he founded Hughes Aircraft, at first in a rented corner of a Lockheed hangar in Burbank. With the racing aircraft H-1 he developed himself, he set a speed record for landplanes in 1935, followed in 1937 by a record flight across the USA. The H-1 now stands in the National Air and Space Museum in Washington.

In 1938, Hughes flew around the world in a Lockheed 14 Super Electra in about 91 hours. From 1939 he bought into the airline TWA – Trans World Airlines and held the majority from the mid-1940s. Together with TWA president Jack Frye, he set the development of the Lockheed Constellation in motion, one of the most elegant airliners of the piston-engine era.

In July 1946, in the middle of work on the H-4, Hughes crashed the XF-11 reconnaissance prototype over Beverly Hills and was seriously injured. He recovered and a good year later sat at the controls of his flying boat himself. His company later also gave rise to the helicopter division, whose best-known product still flies today as the Hughes 500 or MD 500.

The Senate, the criticism and the one flight

When the H-4 was finished, the war was over. Critics saw the wooden giant as a prime example of wasted taxpayer money, the press mocked the “Spruce Goose” – even though it wasn’t made of spruce at all. Hughes himself hated the nickname. In August 1947 he had to testify before a US Senate investigating committee that was examining the use of government funds for his aircraft projects. Hughes defended the project vehemently and stressed how much personal work he had put into it.

How high and how far the H-4 flew that day is reported differently. The museum speaks of about 25 feet of altitude, just under half a mile and about 30 seconds. Other accounts cite around 70 feet, about a mile and 26 seconds. What all sources have in common: the H-4 stayed in ground effect, the zone just above the water surface in which a wing gets additional lift. Whether it would also have flown safely at a greater altitude remains a subject of debate among aviation historians.

Three decades in the hangar

After the flight, Hughes did not have the H-4 scrapped. He put it in a purpose-built, air-conditioned hangar in Long Beach and had a permanent crew look after it. At times about 300 people are said to have been employed for this; in 1962 the team was cut back significantly. Only after Hughes’s death in April 1976 did this care end. All in all, the public did not get to see the flying boat for three decades.

After that, it was unclear what should happen to the giant. Parts of the Hughes estate went to the Smithsonian Institution, while the H-4 itself stayed in the hands of Hughes’s company, Summa Corporation. It gave it to the Aero Club of Southern California, which leased it onward for exhibition.

Under the dome next to the Queen Mary

In the 1980s, the Spruce Goose became a tourist attraction in Long Beach: it stood in a huge domed hall right next to the ocean liner RMS Queen Mary. In 1988, Disney took over the attractions at the harbor. In the early 1990s, the company decided to stop exhibiting the flying boat, and the Spruce Goose needed a new home.

The journey to Oregon

In 1992, a museum project in McMinnville in Oregon, founded by Michael King Smith and his father Delford M. Smith, got the nod. Delford Smith is known to many spotters as the founder of the Evergreen group, which also included the cargo airline Evergreen International Airlines with its Boeing 747s.

The move was an adventure in itself. The H-4 was disassembled and brought north along the West Coast on barges, then up the Columbia River and the Willamette River as far as Portland. There it had to wait for months until the water level allowed passage under the bridges. It covered the last stretch by road. After around 138 days and over 1,600 kilometers, it arrived in McMinnville at the end of February 1993.

The real work began afterward: restorers and volunteers put the flying boat back together over years of work. On June 6, 2001, the museum opened with the fully assembled Spruce Goose as its centerpiece. Volunteers play an important role in projects like this – how that works in aviation museums is described in the piece on volunteering in aviation museums.

The Spruce Goose in size comparison

For decades, the H-4 was the yardstick when it came to wingspan. Not until April 13, 2019, did an aircraft with an even larger wingspan fly, the Stratolaunch Roc, at around 117 meters. In length and weight, however, widebody jets and freighters had long since overtaken the H-4. You’ll find the full ranking in the overview of the largest aircraft in the world.

Feature	Dornier Do X	Hughes H-4 Hercules	Antonov An-225	Airbus A380-800
First flight	1929	1947 (only flight)	1988	2005
Wingspan	48.0 m	around 97.5 m	around 88.4 m	around 79.8 m
Length	around 40.1 m	around 66.7 m	around 84 m	around 72.7 m
Powerplant	12 piston engines	8 piston engines	6 jet engines	4 jet engines
Design	flying boat	flying boat	landplane	landplane

The Dornier Do X was the largest aircraft in the world in 1929 – a flying boat like the H-4, but only half as wide. The Antonov An-225 was the heaviest aircraft in service until its destruction in 2022, and the Airbus A380 is the largest passenger aircraft in scheduled service. None of them, however, reaches the wingspan of the Spruce Goose.

By the way: the name Hercules occasionally misleads spotters. The H-4 has nothing to do with the Lockheed C-130 Hercules, the four-engine turboprop transport – other than the name of the Greek hero.

Why the H-4 failed

The H-4 was an impressive feat of engineering, but an aircraft at the wrong time.

Large flying boats rapidly lost importance after World War II anyway. Land airports with long runways were built in many countries, and landplanes like the Constellation or later the jets crossed the oceans faster and more cheaply. The era of the large passenger flying boats such as the Boeing 314 Clipper thus came to an end as well.

Visiting the Spruce Goose

The H-4 now stands in McMinnville, about 40 miles southwest of Portland in the Willamette Valley wine country. For decades the museum was known as the Evergreen Aviation & Space Museum and now goes by the name North American Aerospace Museum. You’ll find detailed information on the museum and its collection on the page for the Evergreen Aviation & Space Museum.

The Spruce Goose almost fills the large exhibition hall on its own. Under its wings and around it stand numerous other aircraft that look almost like models next to the giant. If you want to go inside, according to the museum you can take short guided tours to the upper flight deck. The groups are small, and the spots are assigned on the day of your visit and are often quickly gone. Check opening hours, tour offering and admission directly with the museum before your visit.

Combining it with other destinations

A trip to Oregon combines well with further aviation destinations in the northwest of the USA. In the greater Seattle area, the Museum of Flight awaits with its large collection on the history of Boeing. If you also travel on to California on the West Coast, in Los Angeles you can visit the places where the H-4 was built and flown. For planning, the tips for a spotting trip to the USA and the overview of what is allowed when plane spotting in the USA are worthwhile.

Conclusion

The Hughes H-4 Hercules is a monument to ambition, perfectionism and bad timing. Built as an answer to the U-boat threat in the Atlantic, it was finished only when nobody needed it anymore. Its single flight in Long Beach harbor lasted only about half a minute, but was enough to back up Howard Hughes’s claim that his wooden giant could fly. Today the Spruce Goose is the largest flying boat in history and one of the most impressive museum pieces in the world.