You had worked with the director Sam Mendes a few times before, including on the 007 movie “Skyfall.” Was it a given you would do “1917”?

It wasn’t a given he was going to ask me. [Laughs] No, he called out of the blue and said he was going to be doing something shortly, and could he send me a script? It turned up and on the front cover, it said, “This is envisioned as a real-time story, shot with a single take.” That was a bit of a shock, but I read the script, and it seemed like an interesting way to tell the story. It wasn’t a tacked-on gimmick.

What was the toughest challenge?

Figuring out the right balance of the shot. Are you behind them [the soldiers] all the time? How often do you have to be on their faces? Is it too claustrophobic to pull them all the way down a trench? Once we settled on the feel of the camera, then it was just a technical challenge to figure out how to break our one shot down into sections so it was manageable.

I know you don’t want to reveal any secrets, but how many shots make up the film?

I really don’t want to say, but we were shooting for 65 days. I never really timed it, but I think the longest shot was about seven minutes. There were also takes that were very short because they were little stitching pieces.