AFTER the juggling act of two Bond films, with their cadre of characters and armory of gadgets, Sam Mendes had something cleaner in mind for his next film.

Two main characters. No backstory. Real time. And one shot.

From the start, Mendes envisioned his “1917” as unfolding continuously and breathlessly. In the British trenches of World War I, two soldiers are tasked with delivering an urgent message to stop an attack planned for the next morning that’s doomed to fail. The Germans have stealthily retreated.

Mendes, working with cinematographer, Roger Deakins, and production designer, Dennis Gassner, (both collaborators on Mendes’ 007 epic “Skyfall”), follows their harrowing journey without hiding any edits, giving the film a ceaseless and fluid quality.

For the 54-year-old Mendes, renowned for his inventive stagings (he won a Tony earlier this year for directing “The Ferryman,” and this March will bring “The Lehman Trilogy” to Broadway), the film is an especially bold enterprise, one that extends the cinematic history of the long take, in movies such as “Rope,” “Russian Ark” and “Birdman” into a new realm.

Before “1917” lands in select theaters on Christmas Day, Mendes discussed why he hopes people are drawn in by his technical achievement but, as soon as the lights go down, forget it.

Q: You opened “Spectre” with a great long take. Is that when you started thinking about more elastic ways to shoot?

A: That was one I was really proud of and enjoyed as well. I loved the process of doing it. It asks you to think of the multiple ways a camera can tell a story that are not close-up, close-up, over-the-shoulder, over-the-shoulder, two-shot, push-in through the door. I found myself quite quickly defaulting to standard ways of telling a story. Just coverage, coverage and more coverage. The challenge here was to make it on the day and not in post. You feel like everyone’s making it on the day because everyone knows there’s no way out of this. This is the movie. And every single member of every department is engaged on every shot. Normally, it’s like, “Well, we’re in close-up so special effects can go have some breakfast. And now we’re on a shot of a building blowing up, the hair and make-up isn’t so important.” But here, everyone was engaged in every second of the film. It happened at the beginning of “Spectre.” Everyone was maxed out, and I love that feeling.

Q: Were you concerned that it could come off like a gimmick?

A: We experience life as a single shot. We go through life with one unbroken take. It’s editing that’s the gimmick. Editing is a wonderful tool if you want to jump time, jump space, jump from one story to another. But editing is so overused in just a basic scene. You and me talking, we would have already used five or six different setups. You have to ask yourself: Why is that now our default?

Q: How extensive was the rehearsal?

A: The difference between this and a normal movie is that the actors started prep with the crew. We couldn’t build anything or judge anything until we had physically rehearsed the journey we were going to take. Everything started on empty fields with scripts in hand, planting flags for the trenches and no man’s land. This is the distance, this is where the trenches cross, etc. Then you extrapolate that onwards through vast areas of land. Only then could we start digging the trenches, and we dug over a mile of trenches and filled them with people. Every step of the journey was accounted for.

Q: Early in the film, one of the soldiers hurts his hand on a barbed wire. Does that cut precede the first film cut?

A: There are a couple of cuts beforehand but I wouldn’t call them cuts. Blends, stitches, whatever you want to call them. Morphs. On the whole, there were long takes of five, six minutes, as long as eight and a half. Even if you know what it’s going to be going in, I hope you forget about it and get immersed in it. The goal is to remove as many layers between the audience and the characters as much as possible, not add them. So we never moved the camera in a way that was self-advertising. It’s a constantly shifting dance between the subjective and the objective, between being intimate and being epic.

Q: To prepare, did you go back and watch Hitchcock’s “Rope” or 2002’s one-take “Russian Ark”?

A: I had seen “Rope,” I had seen “Birdman.” And not just one-shot movies but movies that deal with long, continuous takes. I thought “Children of Men” was a masterpiece of camera work and poetry. I didn’t go back to look at them because even the movies that are most similar to it are quite dissimilar. “Birdman,” for example, which is a movie I loved, is a very surreal film. It’s not asking you to experience time. It’s asking you to forget about it, in a way. “Son of Saul,” which is an absolute masterpiece, is very subjective. It’s very shallow depth of field, everything drops out of focus. That wasn’t like our movie, either. So wherever we looked, it was like, “Well, that’s not quite what we’re doing.” We had to make up our own rules.

Q: This is your fourth film with cinematographer Roger Deakins. On “Skyfall,” you together reached a high level especially in the moving neon reflections of the Shanghai tower scene. Was it a given you’d reach out to him?

A: Yeah, it’s pretty much a given that I try to get him to do anything. The answer is yes or no, or he’s doing a movie with the Coen brothers and he’s not available. I’ve been fortunate to work with him from the beginning and particularly on this one. For that scene, Dennis Gassner, who also designed this movie, built the office tower in Shanghai as a model and then we would move all the LED screens to begin to understand how the reflections work within those glass cubes. I remember sitting for hours with the lights off in the room in Pinewood with Roger and Dennis trying to work out how we would construct it. We did a similar thing with this, Dennis building a model of the town and putting the flares on tiny wires so we understood how the shadows fell and the big church in the center of it aflame and how the light from that would streak through and intersect with Scofield’s journey.