 Homemade submachine guns are often made by copying existing designs, or by adapting simple, open-bolt actions and leveraging commonly available hardware store parts.The Błyskawica (Polish for "lightning"), was a submachine gun produced by the Armia Krajowa, or Home Army, a Polish resistance movement fighting the Germans in occupied Poland.Together with a Polish version of the Sten sub-machine gun, with which it shares some design elements, it was the only weapon mass-produced covertly in occupied Europe during World War II.