The director of 'Greyhound' says his WWII movie about an ocean battle was filmed without a single drop of water

• "Greyhound" director Aaron Schneider told Insider how the movie was made without any water.
• The movie uses a combination of CGI, photogrammetry, and gamer tech to make the ocean battles look real.
• That's impressive given the entire movie is based around a battle at sea.
• Schneider filmed on a partial piece of a destroyer built on a soundstage surrounded by a green screen.
• He also used a program often used in the gaming world called NVIDIA WaveWorks which created an open ocean environment.

Gone are the days when movie productions would have to film on a large body of water to tell stories set out in the ocean. But it's still rare not to use any water to make that kind of movie.

Turns out that's what the Tom Hanks World War II high seas movie "Greyhound" (available now on Apple TV Plus) pulled off thanks to a mix of dazzling CGI and game developer tech.

Director Aaron Schneider ("Get Low") admits he's always been taken by the tech side of the business — before directing he was a cinematographer for years. But while teaming with Hanks to direct the star's script about an inexperienced US Navy captain (Hanks) whose destroyer leads a merchant ship convoy against German U-boats during World War II, Schneider got to go full-on geek.

10,000 photos of the USS Kidd were taken to create a 3D model of the destroyer in 'Greyhound'

Though Schneider and Hanks had been talking about making "Greyhound" since late 2017, the urgency by Steven Spielberg to make "The Post" (in which Hanks plays Washington Post editor-in-chief Ben Bradlee) put things on hold.

That turned out to be a huge benefit for Schneider. He used that time to heavily research the battleships and submarines that took part in the "Battle of the Atlantic," which is what "Greyhound" is loosely based on.

Instead of reading a few books and watching a couple of World War II movies, Schneider built a website of everything he needed to know about US Navy battleships and German submarines.

"Pictures, YouTube links, Wikipedia pages, high-resolution Navy archive photographs. I collected all these things and built a research website that was indexed and categorized in a way that as the crew came on the movie, they could take a deep dive into whatever they wanted," Schneider told Insider.

Then he went a step further. The director and a friend flew to Baton Rouge, Louisiana, and took around 10,000 photographs of the retired USS Kidd, which is one of the last existing destroyers still in World War II configuration.

Those photos were then used to create a photogrammetry — essentially a 3D model — of the entire destroyer. Schneider used the model to figure out where he would place the camera when shooting the movie while keeping the claustrophobic feel of being on a destroyer.

Finally, it was time to shoot the movie in early 2018, but the tech didn't end.

'Every drop of water in the movie is digital'

"Every drop of water in the movie is digital," Schneider said. "Anything you see out the window or over Tom's shoulder. In fact, most of the fire is digital, too."

Typically a movie set at sea will at some point have scenes shot in a giant water tank, but that wasn't the case with "Greyhound." The chilly Atlantic Ocean, the thrilling battles between the destroyers and U-boats, and even the ice that builds up outside the ship's pilothouse was all created with CGI.

Thanks to the photogrammetry of the USS Kidd, the production knew the layout of every inch of a World War II-era destroyer. That was vital in how it built the pilothouse and balconies that we see Hank's Commander Ernest Krause character navigate through most of the movie, which was all built on a soundstage surrounded by a green screen.

Those scenes were then matched by CGI shots of the rest of the massive ship.

A program called NVIDIA WaveWorks created the movie's authentic ocean battles

To really get the feel that Krause and his destroyer were at sea, Schneider used NVIDIA WaveWorks, a plug-in program usually used by game developers that provides interactive ocean simulation.

"It creates an open ocean and floats an object on the ocean based on the physical mass," Schneider said. "So if I type in the model type of a boat, it will float that object the way it would be on the ocean."

In other words, the program provided realistic blocking for the movie's boats based on real-life physics. The location of the destroyers, merchant ships, and the U-boats and battle sequences were all done through WaveWorks.

"The goal was always to use real physics into believing that this was actually photographed in a real-world kind of way," Schneider said. "If you wanted a big close shot where the ship goes by, well, if you were doing that in real life you could be on a little Zodiac, but a Zodiac floats differently on the water than a big camera ship, so you tell the program, 'float me on a Zodiac' and then all of a sudden the sea is affecting your camera ship much differently but still in a physically real way."

The result is a thrilling 90-minute movie of non-stop battles on the high sea. But as we've learned here, the real bit of movie magic was that Tom Hanks was dry and warm the whole time while filming his scenes.

"Greyhound" is currently available on Apple TV Plus.