LOS ANGELES – When Hollywood heavyweights Steven Spielberg and Tom Hanks team up on a World War II drama, you can expect big things.

And according to actors Austin Butler and Callum Turner, big is what you get with Masters Of The Air, the historical miniseries produced by Spielberg and Hanks – reportedly at a cost of more than US$250 million (S$335 million).

Spielberg, the 77-year-old American film-maker behind Oscar-winning war epics such as Schindler’s List (1993) and Saving Private Ryan (1998), “describes this as the biggest production he’s been a part of”, Turner says.

Debuting on Apple TV+ on Jan 26, the nine-part series tells the story of the United States’ 100th Bomb Group, which carried out daring B-17 raids over Nazi Germany.

Nicknamed “The Bloody Hundredth”, the unit had the dubious distinction of seeing the highest casualty rate in the American armed forces, with three-quarters of its men ending up dead, injured or captured by the end of the war.

The series is a companion piece to 2001’s Band Of Brothers, the acclaimed World War II series co-created by Hanks and Spielberg three years after the pair collaborated on Saving Private Ryan.

The 100th Bomb Group was commanded by Majors Gale Cleven (Butler) and John Egan (Turner), two gifted pilots, charismatic leaders and best friends.

For Butler and Turner, playing the soldiers and filming on vast, purpose-built sets in England was like stepping back in time.

“It was completely immersive,” says Turner, 33.

The creators and production team “left no stone unturned and gave us everything. The base where the characters lived and ate, it’s all real. There was even a church for the chaplain”, he added.

“It was a live airport with runways and we had three B-17s that we played around in.

“And when they built all that, they gave us a map. That tells you how big it is,” says the English star, who appeared in the 2018 to 2022 Fantastic Beasts fantasy films.

The actors did everything they could to learn about this period of history and get into character.

Butler, 32, threw himself into reading as much material as he could on that time period. This included the 2006 non-fiction book the series is based on, Masters Of The Air: America’s Bomber Boys Who Fought The Air War Against Nazi Germany.

The American actor, who received an Oscar nomination for his breakout role in the musical biopic Elvis (2022), also obsessively watched and rewatched home movies provided by Major Cleven’s family.

“That was a gold mine for me as far as getting his cadence and his personality,” says the star, who was in the comedy-drama Once Upon A Time In... Hollywood (2019).

But what helped the actors more than anything was the army boot camp they had to do.

“That was the thing that bonded us all and set the foundation for how we would relate to one another,” Butler says.

“Everything from how to march and salute to history lessons on World War II, it was all in the boot camp.”

Like many who will watch the show, the actors were initially unaware of this story and the heroism of these men.

“But there’s an abundance of information out there. There are websites dedicated to the 100th and to these men, and deservedly so,” Turner says.

Delving into this chapter of history is also a reminder of what was at stake in World War II, the actor adds.

“Discovering what they did and how they changed the tide of the war was so important. It truly is an honour to represent these guys, and to serve their legacy was a privilege,” he says.

• The first two episodes of Masters Of The Air debut on Apple TV+ on Jan 26. The remaining seven episodes will air every Friday through March 15.