Duxford, England (CNN) — We sit facing each other on long metal benches, June sunshine coming in strips through the small rectangular windows.

The roar of the airplane silences chatter, so we wait alone with our thoughts.

On June 6, 1944, the Douglas C-53 "Skytrooper" in which we now sit was filled with American paratroopers, young men far from home, who took off from England's RAF Aldermaston Airfield to be dropped into Nazi-occupied France.

The D-Day landings were an Allied assault by air, land and sea which would change the course of World War II. The soldiers who went out the door, whose steps we've just climbed, leaped to an uncertain fate, enemy snipers shooting at them as they made their descent.

Now, to mark the 75th anniversary of that day, around 30 Douglas planes -- known as "Dakotas" -- have flown to the Imperial War Museum Duxford , north of London, for the largest gathering of the aircraft since World War II.

We're on a rehearsal flight, ahead of the team flying in formation to Caen-Carpiquet Airport in Normandy on June 5.

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D-Day Doll

"I love this airplane," says Bill Prosser, wing leader of the Commemorative Air Force's Inland Empire Wing

He and his team of 80 enthusiasts -- "about half a dozen pilots, a few mechanics and the rest are just volunteers and lovers of history" -- have spent two-and-a-half years getting their plane, D-Day Doll, ready for this event.

The US-based Commemorative Air Force acquires, restores and preserves combat aircraft, and Prosser's unit, based in Riverside, California, took charge of D-Day Doll in the late '90s.

The plane, which rolled off the assembly line in Santa Monica in 1943, was now covered in airline livery and "pretty beat up."

It "took a year to get it to fly," explains Prosser. "It's a lot of labor and love. The mechanical parts generally are easy to find" but "the structural parts ... are hard to come by" and "have to be re-manufactured by hand. There's just a lot of day-to-day maintenance."

The team are all volunteers, and all their money comes from fundraising. The restoration work for today cost $250,000, "and that's before we even left Riverside," says Prosser. "All of the operational cash is over and above that. It's all through donations of folks that want to keep the history alive that keeps this girl flying."

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Honoring veterans

At 65 feet in length and with a wingspan of 95 feet, the Douglas C-53 was "the large transport airliner of the day," explains Prosser. "The Dakotas moved masses. They could take 25 to 30 people at a time, drop them, return, drop them, return."

It carries around 820 gallons of gas and guzzles around 100 gallons per hour. The journey from California to England, in this austere war machine without modern insulation or even a toilet (a portable one was installed), was epic, to say the least.

Between leaving the US and reaching England, there were stops in Canada, Greenland, Iceland and Scotland.

"We spent quite a bit of time coming across North America and ... it really turned into a veteran appreciation at each stop," says Prosser. World War II veterans would come to see the aircraft they flew in 75 years before, and "it gets emotional."

"To honor those individuals that gave so much for us, it's our privilege to take this airplane and display her," he adds.

There are World War II veterans visiting D-Day Doll in Duxford today, such as 97-year-old American pilot David Hamilton. It's a poignant reminder that this will be the last major D-Day anniversary at which survivors might be present.

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'Flies like a motor home'

Despite D-Day Doll being 77 years old -- "a grandma," Prosser jokes -- our ride in the plane is surprisingly smooth.

"It's a very stable airplane," says Prosser, who retired from his career as an airline pilot in the mid-1990s. "It is not the funnest airplane to fly. It flies like a motor home. You turn the control wheel and you wait and then it turns. But it's just the history that's in it."

Prosser and his team of smiling, silver-haired Californians appear to be having an absolute blast at Duxfield, with a passion for aviation history that's infectious.

Keeping D-Day Doll airworthy is a full-time business, with safety being the number one priority. "Even though the engines may be 75 years old, they still are re-manufactured periodically," Prosser explains. "We go through her four times a year for inspections."

So what drives Prosser to put all this love and effort in one plane?