Anthony Fokker developed the synchronized firing mechanism which allowed a machine gun to fire through the arc of the plane's propeller without the bullets hitting the propeller.
Is ws attached tot the cam shaft of the plane's engine, as the propeller would make its pass in front of the machine gun's muzzle the mechanism would stop the function of the gun allowing the propeller Blake to pass in front of it without being shot. Then the gun would start again and repeat this process.
Before this the guns were place on the top wing firing over the propeller arc, decreasing accuracy. With the guns in front of the pilot, he could now more effectively point his gun at the enemy with his plane and increase his accuracy.