The VFX team had to take great care in those scenes to match sun glints and reflections that would occur with the planes at such altitude. "For most of the shots in the gimbal it was shot without glass, so we had to put that in as well. Therefore, we had to fake the reflections and the glints," continues Hammack. "If an actor went in a complete 360-roll, we had to simulate that on the computer-generated stuff, which was relatively easy. But, the actor wasn't going through that light because they couldn't roll the gimbal on set. You cheat the actor by faking some shadows going across them, and then you have to be creative with how you do your computer graphics cockpit, because it has to fit into the same cheats. It got very tricky to be able to make that stuff real."

Then there were the dogfights. "In those wide scenes the planes needed to be doing some pretty dramatic moves and evasive actions," Hammack says. "It needed to be impressive and fast, but there's only so much movement those gimbals can go through and they are certainly not moving fast. For those scenes, we had to go in and manipulate the photography so the actors' faces married into the highly dramatic wide views."

© Lucasfilm Ltd. & TM. All Rights Reserved.

The main challenge was the high-speed destruction. ILM has lots of tools for destruction (most recently on display in Transformers: Dark of the Moon). But once you try to apply those tools and techniques to planes that are flying at 300 miles an hour, it all starts to break down. There is physics to high-speed pyrotechnics that general fluid simulation software can't handle for continuous flow. "And there's no real continuity frame to frame under these conditions," Hammack suggests. "The profile of the fire changes so that it would take an exorbitant amount of frame calculation." So ILM found the perfect solution in Plume, the GPU simulation engine (in collaboration with NVIDA), which is very art direct-able.

As far digital mattes, there was a lot of work that went into building cloud tools. All the companies ended up landing on the same technique: a background of 360-degree cycle clouds, a mid-ground layer of more volumetric clouds to get the nice parallax and to be able to use as a tool for the planes to maneuver around. Then there were the foreground card clouds that are the high-speed that flip by to give a sense of speed."

© Lucasfilm Ltd. & TM. All Rights Reserved.

The work was divided by reels: Pixomondo did the rest of reel one after the opening dogfight involving the destruction of a German train -- very dynamic and in your face-- and reel four involving a bomber run; UPP did reel two involving the Red Tails' first mission, a major dogfight and the destruction of a German airbase; Rising Sun did reel three involving the start of getting the new P-51 Mustangs; Ollin did reel five involving a German prison camp; and UPP did reel six involving the final dogfight with German jetfighters.

"Everyone uses different technologies and a different rendering packing so maintaining looks became a challenge and a compositing problem," Hammack notes. "We established the look for everything with assets and sent out turntables for everyone to visually match along with lighting and environment set ups.

But overall this was an opportunity to show a more realistic-looking World War II aerial film, with hundreds of planes in the air. "We were not bound by the number of practical planes they could get. This was very exciting to provide a first-time epic scale," Hammack concludes.

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Bill Desowitz is former senior editor of AWN and editor of VFXWorld. He has a new blog, Immersed in Movies (www.billdesowitz.com), and is currently writing a book about the evolution of James Bond from Connery to Craig, scheduled for publication this year, which is the 50th anniversary of the franchise.