Yes. The patches were on all fighters, to prevent the guns freezing from 'Damp Cold' at altitude, and to stop dirt ingress on the ground. The patches were fabric, 'stuck' with a red dope, and applied after each sortie where the guns had been fired.When the guns were fired, the patches were torn and smoke stained, as seen in the well-known film clip, a close up of a Spitfire's guns being fired, shown in nearly every production about WW2 air fighting.