WWI Machine Gun Shot Medium Format Film Instead of Bullets

The Mark III Hythe Machine Gun Camera was a camera designed to mimic the American-made Lewis machine gun, and was used by the British air force during World War I to train their aerial gunners in air-to-air combat. The reason was that 120 film was much cheaper than live .303 ammunition, and that the resulting photographs would inform the evaluators of how accurate the pilot was during the combat simulation. To train the gunners in changing magazines, the gun camera included a fully functional — albeit useless — Lewis gun magazine.

Needless to say, this camera would probably give you problems if you were to use it nowadays.