Early years of #militaryaviation and #fighterpilots often had to be careful about how much they fired their forward #machinegun because firing it would slowly eat away at their own propeller. Fortunately for fighter pilots, by #WWII a "synchronization gear" or "interrupter" had been developed and was standard equipment on fighters flown by both the allied and axis powers.

In it's simplest form, the "synchronization gear" is something like a series of raised bumps on the main #propeller shaft. The bumps would be lined up with propeller blades so when the raised bump has rotated toward the machine gun the propeller blade would also be in front of the machine gun.

The bump on the shaft would momentarily separate the pilot's trigger from the machine gun. As a result, the machine gun would stop firing (aka be interrupted) for a fraction of a second as the propeller would sweep past the machine gun barrel. Later in WWII this technology mattered much less as jet engines made the entire concept obsolete.

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