When Gary Oldman first saw himself in full Winston Churchill drag—fat suit, prosthetics, and all—even the veteran actor gasped in shock.

“Sometimes I would walk to the set and pass a mirror. I’d catch myself in the mirror and go, ‘Ahh!’ It was stunning,” Oldman told Vanity Fair Wednesday at the New York premiere of the film that transformed him into Churchill, Joe Wright’s period drama Darkest Hour. “We had a number of makeup tests, and I think I wore the makeup in total 61 times—over 200 hours in the makeup chair. There’s something very special when you’re in the makeup chair, and about two hours and 45 minutes in, you start to look in the mirror and you see the spirit of the man. It’s remarkable.”

The 59-year-old star is earning rave reviews and major awards buzz for his disappearing act as Churchill. In the film—out Nov. 22—the newly appointed prime minister of England is confronted with the ultimate choice: negotiate with Nazi Germany or lead his nation into war against Adolf Hitler despite the British and Allied troops cornered on the beaches of Dunkirk.

“This was the hardest job I’ve ever done as an actor,” Oldman admitted. “It was scary. There were days when I thought, ‘What have I let myself in for?’ Not only the physical nature of the role, but he is such an iconic figure. There was fear. Once I started to find out who the man was, I never enjoyed anything so much in my life.”

To understand the prime minister and capture his essence, Oldman did extensive research by reading biographies, studying film footage, visiting Churchill’s home at Blenheim Palace, and speaking to Churchill’s family members.

“To become Churchill, it’s like a big sausage-maker. You put all the research in the machine and hopefully out comes the sausage at the end of it,” said Oldman, who has previously brought real-life figures like Sid Vicious, Beethoven, and Lee Harvey Oswald to the screen.

“But I immersed myself. I had little under a year to really work on him, and it’s also like osmosis or a sponge. You soak up his spirit, or hoped to. You step out on the wire, and you know that you are going to get on the other side with the help of Joe, but you just hope that you navigated and hope you don’t fall off.”