On Dunkirk, Nolan strapped an IMAX camera in a plane and launched it into the ocean to capture the crash landing. It sunk quicker than expected. 90 minutes later, divers retrieved the film from the seabottom. After development, the footage was found to be "all there, in full color and clarity."

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From American Cinematographer, August edition's interview with Dunkirk Director of Photography Hoyte van Hoytema -
They decided to place an Imax camera into a stunt plane - which was 'unmanned and catapulted from a ship,' van Hoytema says - and crash it into the sea. The crash, however, didn't go quite as expected.
'Our grips did a great job building a crash housing around the Imax camera to withstand the physical impact and protect the camera from seawater, and we had a good plan to retrieve the camera while the wreckage was still afloat,' van Hoytema says. 'Unfortunately, the plane sunk almost instantly, pulling the rig and camera to the sea bottom. In all, the camera was under for [more than 90 minutes] until divers could retrieve it. The housing was completely compromised by water pressure, and the camera and mag had filled with [brackish] water. But Jonathan Clark, our film loader, rinsed the retrieved mag in freshwater and cleaned the film in the dark room with freshwater before boxing it and submerging it in freshwater.'
[1st AC Bob] Hall adds, 'FotoKem advised us to drain as much of the water as we could from the can, [as it] is not a water-tight container and we didn't want the airlines to not accept something that is leaking. This was the first experience of sending waterlogged film to a film lab across the Atlantic Ocean to be developed. It was uncharted territory."
As van Hoytema reports, "FotoKem carefully developed it to find out of the shot was all there, in full color and clarity. This material would have been lost if shot digitally."