The earliest account of their use is in an article – Fighters in the Field – author Peter Masefield published in The Aeroplane 23rd November 1939. At the end of 1939 Peter Masefield was in France.
“An interesting point is that, as the guns are completely housed in the wings, the gun-ports in the leading-edge are covered over with a strip of doped fabric so no holes are left. This makes quite a difference at the take-off, on the climb and to the top speed as well. When the guns are fired the fabric is shot through at once. It is stripped off and replaced by a new piece when the machine comes down”.