In 1915 – one year into World War I – bullets were too expensive to use in air-to-air combat pilot training. Camera manufacturer Thornton-Pickard had a great idea: Make a machine gun that used film – the Mark III Hythe Machine Gun Camera.
However, at that time there was a shortage of ammo and pilots. The latter could easily be solved by training new pilots, but this training needed a lot of the former. Thornton-Pickard got a great idea: Use a roll of film to record the trainees’ manoeuvring and firing effectiveness. The idea was so good that it’s still used today by Mavericks and Icemen everywhere.
The Hythe worked like the Lewis Gun: The charging handle advanced the film and cocked the shutter, while the trigger fired the shutter. The focus, aperture and shutter speed were fixed. Sadly the magazine was empty and didn’t serve any function except training the pilot in changing it during the training missions. [Ignomini, Camera Classics, Wikipedia, Camerapedia via Dark Roasted Blend]