“Oppenheimer” production designer Ruth De Jong was tasked with building Los Alamos, the home of the Manhattan Project and the Trinity Test site, for Christopher Nolan’s atomic bomb drama. But her most challenging feat was recreating the Oval Office for a sequence in the film’s third act.

At Variety‘s Artisans Screening Series, De Jong told the audience that “Oppenheimer” was originally meant to film the Oval Office scene on location at the Nixon Library in Yorba Linda, Calif., but that fell through seven days before the shoot.

Internally, De Jong began to freak out. “I thought certainly we could move [the scene] to the end of the schedule,” she said, but Gary Oldman, who played President Harry Truman, had an air-tight schedule and could only shoot on that day.

So, De Jong called her supervising art director, Samantha Englander, for help. Very early on, the two had floated the idea of finding a pre-existing build of the Oval Office. They looked no further than HBO’s beloved political satire “Veep.”

Not only was “Veep’s” Oval Office built to scale, but it was lying flat-packed, and Englander still had it on hold. The set would take four to five days to reassemble, so De Jong sent a team of construction coordinators to pull it out. “The crown molding was falling off. It was a mess,” De Jong said.

The “Oppenheimer” team still needed to build a lobby and cabinet room, so De Jong had crews working around the clock for five days. “Gary Oldman had no idea,” she said. “And the paint was still wet.”

De Jong was joined at the panel by costume designer Ellen Mirojnick, editor Jennifer Lame, VFX supervisor Andrew Jackson and composer Ludwig Goransson.

A large part of Jackson’s VFX work involved creating in-camera practical effects to reflect what was going on inside J. Robert Oppenheimer’s (Cillian Murphy) head — moving subatomic particles.

When it came to recreating the Trinity Test itself, Jackson said, “We did six or seven explosions. We shot it from multiple cameras, different lenses, different frame rates, and we had an enormous amount of material. By slowing it down and adding multiple layers … we were able to get very close to the look of the archival footage.”

Watch the full video above.