As aircraft improved, it became essential to shoot down the enemy’s aircraft to prevent them from spotting targets, directing artillery fire, bombing, and carrying out other missions. The obvious way to do this was to use your own aircraft to shoot them down, but this was very difficult. What was needed was a way to fire a machine gun straight ahead, so a pilot could aim the gun by aiming his plane. It was also obvious that pilots needed a way to avoid shooting off their own propeller while doing this. Experiments had been carried out before the war with synchronizing the machine gun with the propeller, so the gun would only shoot when the propeller was not in the way, but no effective solutions were found and there was not a pressing need to continue the experiments. Now there was a pressing need. A French pilot, Roland Garros, working with designers who had carried out these experiments before the war, developed a simpler solution. They put steel “wedges” on the propeller (shown above) to deflect the bullets that would otherwise hit the propeller. It was not an ideal solution, but it worked. (Wikimedia Commons https://commons.wikimedia.org/wiki/File%3AMorane-Saulnier-L-airscrew-with-deflector.jpg)