Valkyrie's opening North African battle features authentic vintage aircraft, CG planes and cloned planes. All images © 2008 United Artists Production Finance, LLC.

Director Bryan Singer has a track record with digital visual effects, having made two X-Men movies. But his latest project, the MGM release Valkyrie, was the polar opposite of a CG "look-at-me" assignment. This World War II tale based on an actual plot to stop Adolf Hitler demanded invisible effects that would help the production recreate 1940's Germany.

For this, Singer called upon veteran VFX Supervisor Rich Hoover and Sony Pictures Imageworks, which had previously worked with the director on Superman Returns. "Valkyrie is obviously not an effects movie per se," says Hoover, whose many credits include Armageddon and Seabiscuit. "There are really two key issues in this film. One is that Colonel Von Stauffenberg, the German officer played by Tom Cruise, lost an eye, a hand and two fingers on his other hand after a battle in North Africa. The second issue was restoring Berlin to a 1943 period look, creating vintage airplanes and augmenting explosions."

While the majority of Valkyrie takes place in Germany, the film opens with the North Africa battle where Von Stauffenberg is gravely injured. "There were real aircraft used, but we also added additional aircraft," explains Hoover. "We had two vintage P-40 airplanes flying overhead and we had strafing runs and bombs going off. The production went all-out to get vintage planes but we had to augment these. Bryan had in mind that there were six planes making strafing runs in pairs from various directions. There are times where we see about four."

"We made both CG planes and we cloned the planes that we filmed, whichever looked best for a shot."

"We also added digital muzzle flashes on the planes, but the battle was primarily practical effects that we rigged. This made it feel very real for the actors and it looked very real in the shots," Hoover notes. The production chose a stretch of California desert to stand in for North Africa, though they scouted Spain, Jordan and Morocco before settling on a location halfway between L.A. and Las Vegas. "In the end," says Hoover, "it was a place close to home that won out."

A lot of Valkyrie takes place on interior locations. Hoover and his team added ceilings and environments outside windows. On the streets of Berlin vfx was used to remove modern technology like security cameras.

Very little dressing of this desert locale was needed in order to create a credible battlefield. But Hoover did have to deal with the inherent problems of filming 200 "soldier" extras with seven cameras rolling. "It was almost impossible not to see multiple cameras and crew huddled around them in many of these shots. We also had shots where 200 extras were running in front of crew members, so we had to do a lot of rotoscoping to get the crew out of shots. But watching the movie, you'd never know it."

While Valkyrie doesn't contain digital extras, Hoover recalls, "We did a fair amount of cloning and patching of actual elements. There are scenes with thousands of soldiers forming squadrons, but we just used one squadron over and over again. We used real photography in the smartest and most realistic ways we could. My attitude was that if there was a way to shoot something in camera that what's we did, even if that meant shooting things in pieces. And it worked flawlessly."

When filming in Germany, every effort was made to achieve historical accuracy, says Hoover. "The filmmakers went way out of their way to research everything. Many of the locations where we shot were the actual locations in Berlin where the real events took place."

"The movie has a lot of conversations that take place on interior locations, and some were stage and some were locations," explains Hoover. "We had a huge set of the German headquarters. There were a few shots where we put ceilings in and added environments outside the windows. In one mountain estate in Austria there was a spectacular view out a picture window. This window worked like a garage door that could rise up. We built the exterior totally digitally and matted it into plate photography of a ski area in Austria. It wasn't the actual location, because there wasn't really anything of that left to shoot, but it was similar in terms of the terrain and what you'd see out the window.

"We also shot on streets in Berlin, where there are blocks of buildings from World War II that are still in existence." Hoover recalls being amazed by what the city of Berlin was willing to do to accommodate the filming of Valkyrie. "The city took down power poles and modern lighting and pretty much restored those streets to what they were back in the '40s. Then we removed everything else, like security cameras. In one day, they took down the whole street so we could shoot over the weekend. And when I drove by on Monday morning it was all back up."