It took the Allies several months to develop their own interrupter gear. In the meantime, they used other solutions to the problem. One was to use pusher aircraft, where the propeller was behind the pilot. This gave an unlimited field of fire forward. Single seat pusher fighters like the DH-4 depended upon maneuverability to keep enemy planes off their tail. In less maneuverable two-seat pusher aircraft, like this FE-2d, defending against an attack from the rear could be more harrowing. (Wikimedia Commons https://commons.wikimedia.org/wiki/File:Royal_Aircraft_Factory_FE2d_gunner.jpg)