The Fokker's sole remaining advantage was its synchronized machine gun, which fired forward through the arc of its propeller. At the time, the Allies lacked a similar system, and the Nieuport 11's Lewis machine gun was mounted to fire over the propeller, allowing uninterrupted forward fire. The Lewis was not synchronizable, due to its open bolt firing cycle design which resulted in an unpredictable rate of fire. Clearing gun jams and replacing ammunition drums in flight were challenging though, and the drums limited ammunition supply.